c mice

KEY WORDS: egg allergy; heat-treatment; high-pressure; BALB/c; sensitization; anaphylaxis;. 33. IgE; IgG1. 34. Page 2 of 32. ACS Paragon Plus Environm...
0 downloads 0 Views 1MB Size
Subscriber access provided by University of Florida | Smathers Libraries

Article

SENSITIZING AND ELICITING CAPACITY OF EGG WHITE PROTEINS IN BALB/C MICE AS AFFECTED BY PROCESSING Alba Pablos-Tanarro, Daniel Lozano-Ojalvo, Mónica Martínez-Blanco, Rosina López-Fandiño, and Elena Molina J. Agric. Food Chem., Just Accepted Manuscript • Publication Date (Web): 03 May 2017 Downloaded from http://pubs.acs.org on May 9, 2017

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

Journal of Agricultural and Food Chemistry is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 32

Journal of Agricultural and Food Chemistry

1

SENSITIZING AND ELICITING CAPACITY OF EGG WHITE PROTEINS IN BALB/C

2

MICE AS AFFECTED BY PROCESSING

3 4

ALBA PABLOS-TANARRO, DANIEL LOZANO-OJALVO, MÓNICA MARTÍNEZ-

5

BLANCO, ROSINA LÓPEZ-FANDIÑO, ELENA MOLINA

6

Instituto de Investigación en Ciencias de la Alimentación (CIAL, CSIC-UAM), Madrid, Spain

7

[email protected];

8

[email protected]

[email protected];

[email protected];

[email protected];

9 10

Correspondence: Elena Molina

11

CIAL, Nicolás Cabrera 8, 28049 Madrid, Spain

12

E-mail: [email protected]

13

Phone: +3491 0017938

14

FAX: + 34 91 0017905

15 16 17

Abbreviated running title: Allergenicity of processed egg white proteins

18

1 ACS Paragon Plus Environment

Journal of Agricultural and Food Chemistry

Page 2 of 32

19

ABSTRACT

20

This study assesses to what extent technological processes that lead to different degrees of

21

denaturation of egg white proteins affect their allergenicity. We focused on heat (80ºC, 10 min)

22

and high pressure (400 MPa and 37ºC, 10 min) treatments and used a BALB/c mouse model of

23

food allergy. Oral sensitization to egg white using cholera toxin as adjuvant induced the

24

production of IgE and IgG1 isotypes and led to severe clinical signs following challenge with

25

the allergen. Extensive protein denaturation caused by heat treatment increased its ability to

26

induce Th1 responses and reduced both its sensitizing and eliciting capacity. Heated egg white

27

stimulated the production of IgE over IgG1 antibodies directed, at least in part, towards new

28

epitopes exposed as a result of heat treatment. Conversely, partial denaturation caused by high

29

pressure treatment increased the ability of egg white to stimulate Th2 responses and its

30

allergenic potential.

31 32 33

KEY WORDS: egg allergy; heat-treatment; high-pressure; BALB/c; sensitization; anaphylaxis;

34

IgE; IgG1

2 ACS Paragon Plus Environment

Page 3 of 32

Journal of Agricultural and Food Chemistry

35

Introduction

36

Food allergy is a major health problem in Western countries, affecting, approximately, 5%

37

of adults and 8% of children and egg proteins are the second leading cause of allergy during

38

infancy and early childhood.1 Although it is a complex scenario, it is broadly accepted that the

39

prevalence and severity of food allergies are increasing alarmingly and the economic and social

40

impact is growing. In addition, so far, there is no approved treatment for food allergy and

41

sensitized individuals need to avoid ingestion of food to which they are allergic.2

42

Thermal processing techniques, commonly used during food production, have the potential

43

to impact food allergens by inducing structural alterations, such as unfolding and aggregation.

44

The effects of temperature on different food allergens have been extensively investigated and

45

there is a general agreement that it is very important to understand how heat treatments alter the

46

structure of food proteins and the subsequent gastrointestinal digestibility, both of them

47

influencing their allergenicity.3-5 Other processing techniques, such as high hydrostatic pressure

48

can also lead to denaturation of proteins depending on the pressure level, temperature, and

49

chemical conditions. Johnson et al.

50

structure and aggregation state of a selection of purified food allergens after high pressure

51

application, although, depending on the protein, pressurization may induce sufficient structural

52

modifications to affect susceptibility to digestion and immunoreactive properties, lowing or

53

enhancing the binding to IgE and the capacity to trigger mast cell activation and produce

54

clinical reactions.4

6

did not observe substantial changes in the secondary

55

Physicochemical changes caused by heat treatment on egg proteins are often associated

56

with a decrease in their allergenicity.7 Heating of egg proteins increases the digestibility of

57

ovalbumin (OVA), the most abundant egg allergen, and lowers the binding of egg allergens to

58

IgE from patient sera;8-10 although the reactivity of IgE from egg allergic patients towards the

59

native or heated forms varies depending not only on whether egg has been extensively of

60

partially cooked, but also on their individual susceptibility.11 However, while oral exposure to

61

cooked eggs is likely to be the most frequent source of immunization, the sensitizing potential

62

of heated proteins administered by the oral route has not been studied in depth. Regarding high3 ACS Paragon Plus Environment

Journal of Agricultural and Food Chemistry

Page 4 of 32

63

pressure treatments, Hildebrandt et al.,12 reported that the IgE-binding of eggwhite allergens in

64

meat products decreases with increasing pressure, from 400 to 700 MPa. It is also known that

65

simultaneous enzymatic treatment and pressurization increases the susceptibility of OVA to

66

hydrolysis by pepsin, trypsin and chymotrypsin.13 Nevertheless, the information available does

67

not allow drawing a clear picture of the effect of mild denaturation treatments on the

68

allergenicity of egg and, in fact, there are no in vivo data on the allergenic potential of

69

pressurized egg proteins.

70

The aim of this study was to investigate to what extent technological processes that lead to

71

different degrees of denaturation of egg proteins affect their sensitization and elicitation ability

72

in a mouse model. We have focused on moderate heat and high pressure treatments, applied,

73

respectively, at 80ºC and 400 MPa for 10 min; which are usual operating conditions in food

74

processing whose effects on the allergenic potential of egg white have not been previously

75

addressed. Raw, heated and pressurized egg white (EW, HEW and PEW, respectively) were

76

orally administered to BALB/c mice. Serum antibody levels were recorded and severity of

77

anaphylaxis was evaluated following allergen challenge. Special attention was paid to the

78

specificity of the generated antibodies and the systemic cytokine profiles.

79 80

Materials and methods

81

Proteins, chemicals and enzymes for in vitro digestion were purchased from Sigma–

82

Aldrich (St. Louis, MO, USA) unless otherwise specified. Antibodies were from BD

83

Biosciences (San Diego, CA, USA). Eggs came from organic-crop fed poultry and were

84

purchased from a local supermarket.

85 86

Egg white proteins

87

Egg white (EW), separated from fresh eggs and commercial egg proteins -ovalbumin grade

88

V (OVA), ovomucoid type III-O (OM) and lysozyme (LYS)- were used. Heated egg white

89

(HEW) was obtained by heating at 80ºC for 10 min and pressurized egg white (PEW) by high

90

hydrostatic pressure treatment (High Pressure Equipment, Stansted ISO-LAB system, Essex, 4 ACS Paragon Plus Environment

Page 5 of 32

Journal of Agricultural and Food Chemistry

91

UK) at 400 MPa for 10 min at 37ºC. Samples were freeze dried, analysed for protein content by

92

the Kjeldahl method (85.12%, 84.70% and 84.23% in EW, HEW and PEW, respectively) and

93

structurally characterized by SDS-PAGE and circular dichroism (CD). The lipopolysaccharide

94

content (analysed by the Pierce® LAL Chromogenic Endotoxin Quantitation Kit, Thermo

95

scientific, Waltham, MA, USA) was below of 1 UE/mg in all proteins and egg white samples

96

except for OVA, which was purified by size exclusion chromatography.14

97 98

Structural analysis by SDS-PAGE and CD

99

Samples for SDS-PAGE were dissolved at 2 mg of protein/ml in sample buffer that

100

contained 50 mM Tris-HCl (pH 6.8), 10% v/v glycerol, 2% w/v SDS and 0.002% w/v

101

bromophenol blue, in the absence or presence of 5% β-mercaptoethanol and heated for 10 min

102

at 95ºC. Electrophoretic separations were carried out at 120 V on Precast Criterion XT 12% Bis-

103

Tris gels (Bio-Rad, Hercules, CA, USA) using XT MES as running buffer (Bio-Rad). Precision

104

Plus Protein Unstained Standard was used as molecular weight marker. Gels were stained with

105

Coomasie Blue, and images were taken with a Molecular Imager Versadoc MP 5000 system and

106

processed using Quantity One 1-D analysis software (all from Bio-Rad).

107

CD was performed as previously described by Benedé et al.15 Far (200-250 nm) CD spectra

108

of EW, HEW and PEW, dissolved at 0.2 mg of protein/ml in phosphate buffer 50 mM pH 7.0,

109

were recorded at 20ºC using cells with 0.1 cm pathlengths in a Jasco J-810 spectropolarimeter

110

(Jasco Corp., Tokyo, Japan). Spectra represent the average of three accumulations collected at

111

20 nm/min, with a 2 s time constant, a 0.2 nm resolution and a sensitivity of 100 mdeg. Buffer

112

blanks were subtracted from each CD spectrum, which were represented as mean specific

113

ellipticity (degree·cm2·cg-1). CDNN secondary structure analysis software (Applied

114

Photophysics Ltd, Surrey, UK) was used.

115 116

In vitro gastroduodenal digestion

117

In vitro digestions were carried out as previously described.16 Briefly, gastric digestions

118

were performed at a protein concentration of 6.4 mg/ml in simulated gastric fluid (35 mM NaCl, 5 ACS Paragon Plus Environment

Journal of Agricultural and Food Chemistry

Page 6 of 32

119

pH 2.0) for 60 min at 37ºC, with 182 units/mg protein of porcine pepsin (EC 3.4.23.1, 4220

120

U/mg protein). Aliquots were withdrawn at 20 and 60 min and reactions stopped by raising the

121

pH up to 7.0-7.5 with NaHCO3. For intestinal digestions, the gastric digests were mixed with

122

0.25 M Bis-Tris, pH 6.5, 1 M CaCl2 and a 0.125 M bile salt mixture, containing equimolar

123

quantities of sodium taurocholate and glycodeoxycholic acid. Pancreatic bovine trypsin (EC

124

232-650-8, type I) and α-chymotrypsin (EC 232-671-2; type I–S), and pancreatic porcine lipase

125

(EC 232-619-9; type VI-S) were added to the mixture at enzyme: protein ratios of 34.5, 0.4 and

126

24.8 units per mg of protein, respectively. Pancreatic porcine colipase (EC 259-490-1) was

127

added at an enzyme:protein ratio of 1:895 (w:w). Duodenal digestions were carried out for 20

128

and 60 min at 37ºC and stopped by adding trypsin-chymotrypsin inhibitor, at a concentration

129

calculated to inhibit twice the amount of trypsin and chymotrypsin present in the digestion mix.

130

The digests were immediately mixed with SDS-PAGE sample buffer and heated as indicated

131

above.

132 133

Animals

134

Six-week-old female BALB/c mice (Charles River Laboratories, Saint Germain sur

135

l´Abresale, France) were kept under specific-pathogen-free conditions and fed an animal

136

protein-free diet (SAFE, Route de Saint Bris, France) and water ad libitum. All protocols

137

involving animals were approved by the CSIC Bioethics Committee and the Comunidad de

138

Madrid (Ref PROEX 089/15) and the European legislation (Directive 2010/63/UE).

139 140

Sensitization and challenge protocols

141

Mice (distributed in 8 groups of 5 animals) were orally administered the amount of EW (3

142

groups), HEW (2 groups) or PEW (2 groups) equivalent to 5 mg of protein plus 10 µg of CT

143

(List Biologicals, Campbell, CA, USA), or just PBS (naïve group). Sensitization was performed

144

during 3 consecutive days on the first week and once a week during the following 6 weeks. On

145

week 8, mice were orally (50 mg of protein) and intraperitoneally (i.p., 100 µg of protein)

146

challenged, 40 min apart. EW-sensitized mice were challenged with EW, HEW and PEW; 6 ACS Paragon Plus Environment

Page 7 of 32

Journal of Agricultural and Food Chemistry

147

HEW-sensitized mice, with EW and HEW; and PEW-sensitized mice with EW and PEW. Naïve

148

mice were challenged just with PBS. Anaphylactic signs and body temperature drops were

149

evaluated 30 min after the oral and i.p. challenges.17 All mice were euthanized at the end of the

150

challenge protocol by CO2 inhalation.

151

At different experimental points, blood samples were collected by cheek puncture and

152

centrifuged at 2000 x g for 15 min. Serum levels of mouse mast cell protease-1 (MCP-1) were

153

quantified post-mortem with a commercial ELISA kit (eBioscience, San Diego, USA), as

154

outlined by the manufacturer.

155 156

Passive cutaneous anaphylaxis (PCA)

157

Following Li et al.,18 20 µl of pooled samples of sera collected post-mortem from five

158

HEW-sensitized mice, either unheated or heat-inactivated (56ºC for 3 h), were intradermically

159

inoculated in the right ear pinna of BALB/c naïve mice (2 mice per treatment). Pooled serum

160

from naïve mice was inoculated in the left ear pinna. Twenty-four hours later, mice were

161

intravenously injected with 200 µg on a protein basis of HEW in 100 µl of 0.5% Evans blue dye

162

(Sigma-Aldrich). Sixty minutes apart, mice were euthanized by CO2 inhalation and ears were

163

individually collected, weighed and incubated overnight at 55ºC in N,N-dimethylformamide

164

(Sigma-Aldrich). The absorbance of the supernatant was measured at 655 nm, corrected with

165

the absorbance of the supernatant from the ear injected with pooled naïve sera, and compared

166

with a standard curve of serial dilutions of Evans blue, in order to quantify dye extravasation per

167

g of mouse ear.

168 169

Indirect ELISA for the detection of specific IgE and IgG1

170

Indirect ELISA was performed by coating 96-well plates with 5 µg/ml (for IgE) or 2 µg/ml

171

(for IgG1) of protein (OVA, OM, LYS, EW, HEW and PEW).17 To build reference curves, plates

172

were coated with rat anti-mouse IgE and IgG1 (BD Biosciences). Blocked plates were incubated

173

overnight at 4ºC with serum samples (1/25 diluted for IgE and 1/1000 or 1/5000 diluted for

174

IgG1). Serial dilutions of mouse IgE and IgG1 were used for the reference curves (BD 7 ACS Paragon Plus Environment

Journal of Agricultural and Food Chemistry

Page 8 of 32

175

Biosciences). Subsequently, plates were incubated with biotin rat anti-mouse IgE and IgG1 and

176

streptavidin-HRP (BD Biosciences). Colorimetric reactions were read at 405 nm in a plate

177

reader

178

ethylbenzothiazoline-6-sulfonic acid) as substrate (Roche, Mannheim, Germany).

(Multiskan

FC,

Thermo

Scientific)

after

addition

of

2,2′-Azino-bis(3-

179 180

Antibody-capture ELISA for the study of the IgE binding capacity

181

EW, HEW and PEW were labelled with EZ-link sulpho-NHS-LC biotin (Pierce, Rockford,

182

IL, USA) using a 5:1 molecular ratio of biotin:protein. Pooled sera from 5 mice sensitized to

183

EW, HEW or PEW (1/100 diluted) were added to plates coated with rat anti-mouse IgE (2

184

µg/ml, clone MCA 419, BioRad) and incubated overnight at 4ºC. For direct ELISA, 50 µl of

185

biotin-labelled antigen (500 ng/ml) were added and incubated for 3 h at room temperature. In

186

the case of the competition assays, mixtures of 25 µl of biotinylated antigen and 25 µl of diluted

187

non-labelled antigen (from 1 ng/ml to 0.5 mg/ml) were added to the plates. After incubation

188

with streptavidin-HRP (BD Biosciences), 3,3′,5,5′-tetramethylbenzidine was added as substrate

189

(eBioscience). The colorimetric reaction was stopped with H2SO4 and read at 450 nm in a plate

190

reader (Multiskan FC, Thermo Scientific). Results were expressed as B/B0, where B0 and B

191

represent, respectively, the amount of labelled EW, HEW or PEW bound to the immobilized

192

IgE antibodies in the absence or presence of a known concentration of non-labelled EW,

193

HEW or PEW.

194 195

Cytokines released by spleen cells

196

Spleen from individual mice were collected and processed as previously described.19

197

Isolated splenocytes were cultured in RPMI 1640 medium supplemented with 10% fetal bovine

198

serum, 2 mM L-glutamine, 50 U/ml penicillin and 50 µg/ml streptomycin (all from Biowest

199

SAS, Nuaillé, France) at a cellular density of 4x106 cells/ml in 48-well plates (non-stimulated

200

control) and incubated with 200 µg/ml (on a protein basis) of OVA, OM, LYS, EW, HEW or

201

PEW. Supernatants were collected after 72 h of culture in 5% CO2 at 37 °C and stored at -80 °C

8 ACS Paragon Plus Environment

Page 9 of 32

Journal of Agricultural and Food Chemistry

202

until ELISA analyses (eBioscience) to quantify cytokine production(IFN-γ, IL-4, IL-5 and IL-

203

10).

204 205

Statistical analyses

206

Experimental results are expressed as means ± standard error of the mean (SEM).

207

Statistical analyses were performed by one-way analysis of variance (ANOVA), followed by

208

Tukey’s test for comparing all groups. Clinical scores are expressed as medians and, in this

209

case, significant differences were determined using the unpaired non-parametric Mann-Whitney

210

test. T-test was used to test differences between unheated and heat-inactivated sera values in the

211

PCA test. The statistical software package GraphPad Prism version 6.0 (GraphPad Software, Inc

212

La Jolla, CA, USA) was used for the analyses. P < 0.05 was considered statistically significant.

213

214

Results

215

Structural changes and digestibility of egg white proteins as a result of heat and high pressure

216

treatments

217

SDS-PAGE analysis under non reducing conditions revealed similar patterns for EW and

218

PEW, although HEW showed a completely different profile characterized by the presence of

219

high molecular mass aggregates and the absence of bands corresponding to the main EW

220

proteins (Fig. 1a). At least part of these aggregates were reduced following the addition of β-

221

mercaptoethanol, with the appearance of bands corresponding to ovotransferrin (OVT), OVA,

222

OM and LYS, which indicates that they were stabilized by disulphide bonds induced by

223

exchanges between free sulfhydryl and disulphide groups of these proteins, while other

224

aggregates, possibly stabilized by non-reducible covalent bonds, remained undissociated (Fig.

225

1a).

226

To unveil further structural differences after processing, far-UV CD spectra were collected

227

and compared (Fig. 2). The spectra of HEW confirmed secondary structure changes as a result

9 ACS Paragon Plus Environment

Journal of Agricultural and Food Chemistry

Page 10 of 32

228

of heat treatment. CD also showed that PEW was structurally similar to EW with respect to the

229

secondary structure content.

230

Following simulated gastrointestinal digestion, there was an incomplete degradation of EW

231

and PEW proteins (Fig. 1b). In particular, OVA partially resisted successive gastric and

232

duodenal in vitro hydrolyses. However, HEW was more susceptible to proteolysis and neither

233

aggregates nor individual native proteins were detected in the SDS-PAGE gels at the end of

234

digestion process.

235

Sensitizing and eliciting potential of processed egg white proteins

236

Serum concentrations of IgE and IgG1 specific to EW and to the individual proteins, OVA,

237

OM and LYS, were determined along the sensitization period by indirect ELISA

238

(Supplementary Fig. 1). Table 1, which compares the antibody levels at the 8th week just before

239

challenge, indicates that HEW-sensitized mice presented a higher amount of EW-specific IgE

240

than mice sensitized to EW. In particular, the OVA-specific IgE response was greater in HEW-

241

sensitized than in EW-sensitized mice, although the LYS-specific IgE response was lower. In

242

addition, HEW-specific IgE was also detected in serum from HEW-sensitized mice at a higher

243

concentration than that of EW-specific IgE. Although the difference did not reach statistical

244

significance, this suggests the formation of IgE antibodies directed towards different antigenic

245

determinants exposed by heat treatment. There were no significant differences in the levels of

246

EW-, OVA- and OM-specific IgE between EW- and PEW-sensitized mice, although LYS-

247

specific IgE was the highest in mice sensitized to PEW. Sensitization to PEW generated

248

comparable amounts of EW- and PEW-specific IgE (Table 1).

249

Sensitization to HEW did not lead to a significant EW-specific IgG1 response as compared

250

with naïve mice. Furthermore, the concentration of HEW-specific IgG1 in the serum of HEW-

251

sensitized mice was also low (Table 1). However, oral administration of EW and PEW plus CT

252

significantly increased the levels of EW-specific IgG1, with PEW-sensitized animals showing

253

equivalent amounts of EW- and PEW-specific IgG1. We detected similar concentrations of

254

OVA-, OM- and LYS-specific IgG1 within each mouse group, and no differences between both

255

groups. 10 ACS Paragon Plus Environment

Page 11 of 32

Journal of Agricultural and Food Chemistry

256

The ability to trigger anaphylactic reactions of HEW and PEW, as compared to EW, was

257

assessed in mice sensitized to EW (Fig. 3). Oral challenge with HEW did not cause a significant

258

drop in temperature as compared with naïve mice administered PBS, nor did challenge with

259

EW, while PEW significantly decreased body temperature in mice (Fig. 3a). Systemic

260

anaphylactic symptoms were evident in all cases, but there were no significant differences

261

among EW-sensitized mice challenged with the EW preparations submitted to processing under

262

different conditions (Fig. 3b). Similar results were obtained after subsequent i.p. challenges,

263

although, in this case, HEW produced the least severe clinical signs. Challenge with HEW also

264

led to the lowest release of MCP-1, indicative of mast cell degranulation (Fig. 3c). Overall,

265

these results imply that HEW and PEW induced, respectively, weaker and stronger anaphylactic

266

responses than EW in EW-sensitized mice.

267

The lower capacity of HEW, as compared with EW, to elicit systemic reactions was also

268

evident in the sign score of mice sensitized to HEW and challenged either orally or i.p. with

269

both preparations. In fact, mice sensitized to HEW did not suffer temperature changes nor

270

anaphylactic sings following challenge with HEW (Fig. 3a and b). However, both PEW and EW

271

caused similar temperature drops, allergic symptoms and MCP-1 release in PEW-sensitized

272

mice. It is noteworthy that significant temperature drops and MCP-1 levels were only detected

273

in mice sensitized to PEW (and challenged either with EW or PEW), as well as in mice

274

sensitized to EW and challenged with PEW, which suggests that, besides a superior ability to

275

trigger allergic reactions, PEW held an enhanced sensitization potential.

276 277

3.3. Specificity of the generated antibodies

278

As mentioned, serum levels of MCP-1 were significantly increased in mice sensitized to

279

EW and PEW (and challenged, respectively, with PEW and either EW or PEW), but not in mice

280

sensitized to HEW (Fig. 3c), despite the later exhibited the highest specific IgE levels (Table 1).

281

This observation prompted us to investigate the ability of IgE generated in HEW-sensitized

282

mice to develop allergic responses. To this aim, we conducted PCA assays with pooled serum

283

heated at 56°C to inactivate mouse IgE antibodies. 18 Passive immunization of naïve mice with 11 ACS Paragon Plus Environment

Journal of Agricultural and Food Chemistry

Page 12 of 32

284

heated serum from HEW-sensitized mice led to a significantly reduced extravasation of Evan’s

285

blue dye to the surrounding tissues upon intravenous challenge with HEW, as compared with

286

the immunization using non-heated serum, denoting that IgE was biologically functional and

287

able to mediate local anaphylaxis reactions (Supplementary Fig. 2).

288

To go deeper into this point, we assessed the binding capacity of IgE present in sera from

289

EW-, HEW- and PEW-sensitized mice to EW subjected to different processing methods using a

290

reverse ELISA based on the capture of mouse IgE antibodies. Initially, we compared the

291

binding capacity of the immobilized IgE molecules towards the antigen used for sensitization in

292

each case by a direct test, which confirmed a higher response in HEW-sensitized mice (Fig. 4a).

293

Competitive ELISA tests, showed that IgE from sera of mice sensitized to HEW bound HEW

294

with a much higher strength than EW and PEW, underlining that sensitization to HEW

295

generated IgE antibodies specific to different or new epitopes (Fig. 4 c). As mentioned above,

296

the observation that, despite allergy in HEW-sensitized mice was mainly IgE-mediated and

297

HEW-specific IgE displayed higher affinity for HEW than for EW (Supplementary Fig. 2 and

298

Fig. 4c), HEW triggered less severe allergic responses than EW in these animals following both

299

oral and systemic challenges (Fig. 3) shows that heating impaired its ability for mast cell

300

crosslinking and activation, given that challenge with EW was able to trigger anaphylactic

301

reactions in HEW-sensitized mice

302

On the other hand, as illustrated in Fig. 4b and d, both EW and PEW inhibited with similar

303

affinity the binding of IgE from sera of EW or PEW-sensitized mice to labelled EW and PEW

304

respectively, whereas HEW was a much weaker inhibitor, particularly of the binding of specific

305

IgE to biotinylated EW. This reveals that heat treatment destroyed IgE-binding epitopes present

306

in EW and that these were maintained when EW was submitted to less severe denaturation

307

conditions, such as 400 MPa applied for 10 min. Additionally, it denotes that sensitization to

308

both EW and PEW induced the production of IgE antibodies with similar specificities.

309 310

3.4. T cell responses in spleen cell cultures

12 ACS Paragon Plus Environment

Page 13 of 32

Journal of Agricultural and Food Chemistry

311

Splenocytes from EW-, HEW- and PEW-sensitized mice were stimulated with the 3

312

protein preparations, as well as with the main egg allergens, OVA, OM and LYS (Fig. 5).

313

Cytokines produced in cultures from naïve mice were undetectable (results not shown). In

314

general terms, spleen cells from sensitized mice within each group released equivalent amounts

315

of IFN-γ, IL-4, IL-5 and IL-10 in response to either the individual proteins or the raw and

316

processed EW forms, with the latter stimulating the highest production. However, splenocytes

317

from HEW-sensitized mice were more prone to Th1 responses, as judged by the release of IFN-

318

γ to the culture media, and those from PEW-sensitized mice released more Th2 (IL-4 and IL-5)

319

cytokines and IL-10, following incubation with the stimuli.

320 321

4. Discussion

322

In this study, the ability of EW subjected to denaturation by means of heat treatment (80ºC,

323

10 min) and high hydrostatic pressure (400 MPa, 10 min) to sensitize and trigger allergic

324

responses was compared in BALB/c mice. Thermal treatment affected egg protein secondary

325

structure and caused polymerization, as determined by CD and SDS-PAGE, in agreement with

326

Mine et al.,20 who described a marked increase in β-sheet and a concomitant decrease in α-helix

327

structure, exposure of hydrophobic residues and aggregation by disulphide bridges with

328

increasing temperature from 60 to 90ºC. On the other hand, and also in accordance with our

329

results, few changes in the secondary structure of OVA and LYS have been reported between

330

the native proteins and those pressurized up to 600 MPa.21-22 High pressure treatments can result

331

in a pressure-dependent exposure of buried sulfhydryl groups leading to EW protein

332

aggregation, although at 40ºC this only occurs above 600 MPa.23 Therefore, the heat and high

333

pressure processing conditions applied led, respectively, to extensive and limited denaturation

334

of EW proteins. Assessment of resistance to simulated gastrointestinal digestion, which is

335

another indicator of structural stability, revealed that, as expected, HEW was far more prone to

336

hydrolysis than EW, which partially withstood digestion, as previously reported for heated and

337

native OVA,9,24-25 whereas EW and PEW exhibited similar susceptibility to proteolysis.

13 ACS Paragon Plus Environment

Journal of Agricultural and Food Chemistry

Page 14 of 32

338

Sensitization to HEW induced IgE antibodies specific to native and denatured EW proteins.

339

In fact, the serum concentration of EW-specific IgE, as determined by indirect ELISA, was

340

significantly higher in HEW-sensitized mice than in EW-sensitized mice, and that of HEW-

341

specific IgE was even greater. Since indirect ELISA does not avoid interactions of plate bound

342

antigens with specific IgG1, which may impair the binding and detection of IgE antibodies, a

343

selective IgE capture ELISA was conducted.26 Even though biotin labelling may vary depending

344

on protein structure, hindering comparison, this method also showed that severe denaturation of

345

EW proteins caused by heat treatment stimulated the production of IgE antibodies which were,

346

at least in part, different in their specificity from those produced upon sensitization with native

347

allergens. In addition, PCA assays revealed that such IgE antibodies were biologically

348

functional in the development of allergic reactions. However, even if HEW was able to generate

349

the most vigorous IgE response, its eliciting capacity, both in EW- and HEW-sensitized mice

350

was very low.

351

It is well documented that heat treatment of egg proteins decreases their allergenic

352

potential. Approximately 70% of egg allergic children tolerate extensively heated eggs and, in

353

these cases, the inclusion of baked egg in the diet accelerates the development of oral

354

tolerance.27-30 The mechanisms responsible for the reduced allergenicity of heat-treated (100° C,

355

5-60 min) EW, OVA and OM were investigated in BALB/c and C3H/HeJ mice. Results pointed

356

at the enhanced digestibility of heated OVA, which reduces its basophil activation capacity, and

357

the impaired absorption of immunologically active forms of the allergens through the intestinal

358

epithelium.24, 31-32 Similarly, in the case of milk whey proteins, heat treatment and subsequent

359

aggregation was reported to promote their uptake from Peyer patches rather than from intestinal

360

epithelium cells, what reduces their capacity to elicit anaphylactic reactions, but enhances their

361

immunogenicity.33 In this respect, while there seems to be a general agreement that severe

362

heating reduces the capacity of egg proteins to trigger allergic reactions, much less is known on

363

the effect of processing on their sensitizing potential.

364

It was reported that mice sensitized by i.p. administration to OVA heated at 70ºC for 10

365

min develop lower levels of OVA-specific IgE than mice sensitized to native OVA.34 However, 14 ACS Paragon Plus Environment

Page 15 of 32

Journal of Agricultural and Food Chemistry

366

in that study, the administration route may have masked the impact of digestion and absorption

367

in the gastrointestinal tract on the immunogenicity of the protein, since both the native and

368

denatured forms were equally recognized by the generated IgE antibodies. Likewise, native and

369

aggregated OVA (80ºC, 6 h) i.p. administered to mice generated similar levels of IgE antibodies

370

specific to either OVA form.35 Following oral administration, the physicochemical changes

371

caused by heat treatment on EW protein structure, and consequent decreased stability towards

372

proteolysis, possibly altered antigen processing and presentation by dendritic cells and T cell

373

priming, ultimately leading to the induction, in HEW-sensitized mice, of IgE over IgG1

374

antibodies with different specificities compared with those produced in EW-sensitized mice. In

375

addition, both structural changes brought about by heat treatment and increased degradation

376

during in vivo digestion could have impaired the ability of HEW for mast cell crosslinking and

377

activation, despite the IgE-antibodies generated showed high affinity towards HEW epitopes.

378

Our results indicate that mice sensitized to HEW by oral administration were more susceptible

379

to Th1 responses than those sensitized to EW, which points at a more equilibrated Th1/Th2

380

balance indicative of a lower sensitization status, an aspect also observed when heated OVA is

381

used for mice immunization through the i.p. route. 34-35 It has been described that different forms

382

of the same antigen can activate distinct patterns of T cell commitment in mice with

383

consequences in the generated antibodies. Thus, OVA chemically modified to give rise to high

384

molecular weight polymers shifts the activation of the OVA-reactive T cell repertoire towards a

385

Th1 phenotype in vivo, what correlates with the antibody responses36. It should be noted that, in

386

our work, spleen cells from HEW-sensitized mice produced the highest level of IFN-γ ex vivo

387

regardless of the stimulus. In fact EW, HEW and PEW induced the same cytokine responses on

388

cells from naïve or sensitized mice, which does not support that heat denatured egg proteins

389

intrinsically stimulate a Th1 profile over a Th2 one. 37

390

Unlike in the case of sensitization to HEW, sensitization to EW and PEW gave rise to an

391

allergic response likely mediated by both IgE and IgG1. Both isotypes can participate in

392

anaphylaxis, in mice, although the IgG1 pathway differs from the classical IgE pathway in that

393

it is mainly triggered by the binding of circulating antigen-IgG1 complexes to FcγRIII receptors 15 ACS Paragon Plus Environment

Journal of Agricultural and Food Chemistry

Page 16 of 32

394

on macrophages, instead of the crosslinking of IgE bound to FCεRI on basophils or mast cells.38

395

IgG1-dependent anaphylaxis in EW- and PEW-sensitized mice could have been facilitated by

396

the large excess of specific antibodies from the IgG1 isotype with respect to the IgE isotype,

397

particularly after the entry of the allergen into systemic circulation. Indeed, despite the fact that

398

the clinical relevance of non-IgE mediated anaphylaxis in humans is controversial, IgG-

399

mediated anaphylaxis can occur in the presence of large concentrations of antigens and of

400

specific IgG antibodies.

401

translated to a human situation, the fact that, in mice, IgE and IgG1 are Th2-driven isotypes

402

induced by IL-4,40 argues for a superior sensitization capacity of EW and PEW over HEW.

39

Thus, even if these results obtained in mice cannot be directly

403

EW and PEW induced equivalent IgE and IgG1 titers and the specificity of the generated

404

antibodies was also very similar. However, spleen cells of PEW-sensitized mice responded with

405

a higher secretion of IL-4, IL-5 and IL-10 to stimulation with either EW, HEW and PEW or to

406

the individual EW-proteins, which denotes a Th2-bias typical of the allergic status and suggests

407

that high pressure processing increased the sensitizing potential of EW proteins. Furthermore,

408

unlike challenge with EW, challenge of mice sensitized to EW with PEW provoked significant

409

temperature drops and mast cell degranulation as compared to naïve mice, suggesting that

410

limited denaturation caused by high hydrostatic pressure increased is eliciting potential. There is

411

some information on the impact of high hydrostatic pressure processing on the IgG- and IgE-

412

binding properties of food proteins4 but, to the best of our knowledge, there are no published

413

data on its effects on the induction of antibody responses and the acquisition of allergic

414

sensitization, or the elicitation of allergic reactions in vivo.

415

It is worth mentioning that, in EW-sensitized mice, the levels specific IgE were in the order

416

OM≥ OVA≥ LYS and there were similar concentrations of OVA-, OM- and LYS-specific IgG1,

417

despite these proteins are present in very different proportions in EW (OVA 54%, OM 11% and

418

LYS 3.5% w/w respectively). It is assumed that OM plays a predominant role in egg allergy,

419

but, in general terms, the contribution of the individual protein components and, in particular,

420

the influence of LYS, is insufficiently known.7 As compared with EW, LYS in HEW generated

421

a significantly lower IgE response, while LYS-specific IgE response in PEW was significantly 16 ACS Paragon Plus Environment

Page 17 of 32

Journal of Agricultural and Food Chemistry

422

higher. LYS is regarded as a thermolabile allergen.41 Unfolding of LYS becomes irreversible

423

when the temperature is above 80ºC, with α-helices being thermodynamically and kinetically

424

more stable than β-structures.42 However, under high hydrostatic pressure conditions (600 MPa,

425

30 min, 40ºC), partial and reversible unfolding of LYS occurs.22 Our results suggest that heat-

426

induced aggregation and enhanced flexibility brought about by high pressure decreased and

427

enhanced, respectively, LYS sensitizing potential, in support of previous findings showing that

428

LYS structure plays an important role in its immunogenicity. In fact, immunization of mice with

429

LYS derivatives of different conformational stability revealed that the least stable derivative

430

leads to the most potent Th2 response and IgE production, which was associated with a higher

431

susceptibility of the unfolded form to be processed by antigen presenting cells.43-44

432

In conclusion, extensive protein denaturation caused by heat treatment of EW not only

433

reduced its eliciting capacity but also its sensitizing capacity in a BALB/c model of egg allergy.

434

HEW stimulated IgE responses over IgG1 responses; however, given the involvement of both

435

isotypes in anaphylaxis in this animal model, the overall result is likely a lower degree of

436

sensitization, reinforced by the observation that HEW-sensitized mice were more prone to Th1

437

responses than EW-sensitized mice. Furthermore, HEW induced the production of antibodies

438

directed towards new epitopes exposed by heat treatment or released as a consequence of the

439

enhanced digestibility of the heated allergen. Conversely, partial denaturation caused by high

440

pressure treatment increased the ability of EW to stimulate Th2-biased responses and its

441

allergenic potential.

17 ACS Paragon Plus Environment

Journal of Agricultural and Food Chemistry

Page 18 of 32

442

References

443

1. Sicherer, S. H.; Sampson, H. A. Food allergy: epidemiology, pathogenesis, diagnosis, and

444 445 446

treatment. J. Allergy Clin. Immunol. 2014, 133, 291-307e5. 2. Bauer, R. N.; Manohar, M.; Singh, A. M.; Jay, D. C.; Nadeau, K. The future of biologics: applications for food allergy. J. Allergy Clin. Immunol. 2015, 135, 312-323.

447

3. Mills, E. N. C.; Sancho, A. I.; Rigby, N. M.; Jenkins, J. A.; Mackie, A. R. Impact of food

448

processing on the structural and allergenic properties of food allergens. Mol. Nutr. Food Res.

449

2009, 53, 963–969.

450

4. Jiménez-Saiz, R.; Benedé, S.; Molina, E.; López-Expósito, I. Effect of processing

451

technologies on the allergenicity of food products. Crit. Rev. Food Sci. Nutr. 2015, 55, 1902-

452

1917.

453 454

5. Verhoeckx, K.; Vissers, Y.; Baumert, J.L.; Faludi, R.; Feys, M.; Flanagan, S.; Kimber, I. Food processing and allergenicity. Food Chem. Toxicol. 2015, 80, 223-240.

455

6. Johnson, P.; Van der Plancken, I.; Balasa, A.; Husband, F.; Grauwet, T.; Hendrickx, M.;

456

Knorr, D.; Mills, E. N. C.; Mackie, A. R. High pressure, thermal and pulsed electric-field

457

induced structural changes in selected food allergens. Mol. Nutr. Food Res. 2010, 54, 1701-

458

1710.

459 460 461 462

7. Benedé, S.; López-Expósito, I.; Molina, E.; López-Fandiño, R. Egg proteins as allergens and the effects of the food matrix and processing. Food Funct. 2015, 6, 694-713. 8. Mine, Y.; Zhang, J. W. Comparative studies on antigenicity and allergenicity of native and denatured egg white proteins. J. Agric. Food Chem., 2002, 50, 2679-2683.

463

9. Jiménez-Saiz, R.; Belloque, J.; Molina, E.; López-Fandiño, R. Human immunoglobulin E

464

(IgE) binding to heated and glycated ovalbumin and ovomucoid before and after in vitro

465

digestion. J. Agric. Food Chem., 2011, 59, 10044-10051.

466

10. Bloom, K. A.; Huang, F.R.; Bencharitiwong, R.; Bardina, L.; Ross, A.; Sampson, H. A.;

467

Nowak-Węgrzyn, A. Effect of heat treatment on milk and egg proteins allergenicity.

468

Pediatr. Allergy Immunol.2014, 25, 740-746.

18 ACS Paragon Plus Environment

Page 19 of 32

Journal of Agricultural and Food Chemistry

469 470

11.Chokshi, N. Y.; Sicherer, S. H. Molecular diagnosis of egg allergy: an update. Expert Rev. Mol. Diagn. 2015, 15, 895-906.

471

12.Hildebrandt, S.; Schütte, L.; Stoyanov, S.; Hammer, G.; Steinhart, H.; Paschke, A. In vitro

472

determination of the allergenic potential of egg white in processed meat. J. Allergy, 2010

473

Article ID 238573.

474

13.Quirós, A.; Chicón, R.; Recio, I.; López-Fandiño, R. The use of high hydrostatic pressure to

475

promote the proteolysis and release of bioactive peptides from ovalbumin. Food Chem.

476

2007, 104, 1734-1739.

477

14.Brix, S.; Bovetto, L.; Fritsché, R.; Barkholt, V.; Frøkiaer, H. Immunostimulatory potential of

478

β-lactoglobulin preparations: Effects caused by endotoxin contamination. J. Allergy Clin.

479

Immunol. 2003, 112, 1216-1222.

480

15.Benedé, S.; López-Fandiño, R.; Reche, M.; Molina, E.; López-Expósito, I. Influence of

481

carbohydrate moieties on the immunoreactivity and digestibility of egg allergen ovomucoid.

482

PLoS One, 2013, 14, 8, e80810.

483

16.Martos, G.; López-Fandiño, R.; Molina, E. Immunoreactivity of hen egg allergens: Influence

484

on in vitro gastrointestinal digestion of the presence of other egg white proteins and of egg

485

yolk. Food Chem. 2013, 136, 775-781.

486

17.Pablos-Tanarro, A.; López-Expósito, I.; Lozano-Ojalvo, D.; López-Fandiño, R.; Molina, E.

487

Antibody production, anaphylactic signs, and t-cell responses induced by oral sensitization

488

with ovalbumin in Balb/c and C3H/HeOuJ mice. Allergy, Asthma & Immunology Research,

489

2016, 8, 239-245.

490

18.Li, X. M.; Schofield, B. H.; Huang, C. K.; Kleiner, G. I.; Sampson, H. A. A murine model of

491

IgE-mediated cow's milk hypersensitivity. J. Allergy Clin. Immunol. 1999, 103, 206-214.

492

19.Lozano-Ojalvo, D.; Molina, E.; López-Fandiño, R. Hydrolysates of egg white proteins

493

modulate T- and B- cell responses in mitogen-stimulated murine cells. Food Func. 2016, 7,

494

1048-1056.

495 496

20. Mine, Y.; Noutomi, T.; Haga, N. Thermally induced changes in egg white proteins. J. Agric. Food Chem. 1990, 38, 2122–2125. 19 ACS Paragon Plus Environment

Journal of Agricultural and Food Chemistry

497 498

Page 20 of 32

21.Smith, D.; Galazka, V. B.; Wellner, N.; Sumner, I. G. High pressure unfolding of ovalbumin. Int. J. Food Sci. Tech. 2000, 35, 361-370.

499

22.Schuh, S.; Schwarzenbolz, U.; Henle, T. Cross-linking of hen egg white lysozyme by

500

microbial transglutaminase under high hydrostatic pressure: localization of reactive amino

501

acid side chains. J. Agric. Food Chem. 2010, 58, 12749-12752.

502

23.Van der Plancken, I.; Van Loey, A.; Hendrickx, M. E. Changes in sulfhydryl content of egg

503

white proteins due to heat and pressure treatment. J. Agric. Food Chem., 2005, 53, 5726-

504

5733.

505

24.Martos, G.; López-Expósito, I.; Bencharitiwong, R.; Berin, M. C.; Nowak-Węgrzyn, A.

506

Mechanisms underlying differential food allergy response to heated egg. J. Allergy Clin.

507

Immunol. 2011, 127, 990–997 e2.

508

25.Nyemb, K.; Guérin-Dubiard, C.; Dupont, D.; Jardin, J.; Rutherfurd, S. M.; Nau, F. The

509

extent of ovalbumin in vitro digestion and the nature of generated peptides are modulated by

510

the morphology of protein aggregates. Food Chem, 2014, 157, 429-438.

511

26.Bernard, H.; Drumare, M. F.; Guillon, B.; Paty, E.; Scheinmann, P.; Wal, J. M.

512

Immunochemical characterisation of structure and allergenicity of peanut 2S albumins using

513

different formats of immunoassays. Analytical and Bioanalytical Chemistry, 2009, 395, 139-

514

146.

515 516

27.Des Roches, A.; Nguyen, M.; Paradis, L.; Primeau, M. N.; Singer S. Tolerance to cooked egg in an egg allergic population. Allergy, 2006, 61, 900–901.

517

28.Konstantinou, G. N.; Giavi, S.; Kalobatsou, A.; Vassilopoulou, E.; Douladiris, N.; Saxoni-

518

Papageorgiou, P.; Papadopoulos, N. G. Consumption of heat-treated egg by children allergic

519

or sensitized to egg can affect the natural course of egg allergy: hypothesis-generating

520

observations. J. Allergy Clin. Immunol., 2008, 122, 414-415.

521

29.Lemon-Mulé, H.; Sampson, H. A.; Sicherer, S. H.; Shreffler, W. G.; Noone, S.; Nowak-

522

Wegrzyn, A. Immunologic changes in children with egg allergy ingesting extensively heated

523

egg. J. Allergy Clin. Immunol., 2008, 122, 977-983.e1

20 ACS Paragon Plus Environment

Page 21 of 32

Journal of Agricultural and Food Chemistry

524

30.Leonard, S. A.; Sampson, H. A.; Sicherer, S. H.; Noone, S.; Moshier, E. L.; Godbold, J.;

525

Nowak-Węgrzyn, A. Dietary baked egg accelerates resolution of egg allergy in children. J.

526

Allergy Clin. Immunol., 2012, 130, 473-480.e1.

527

31.Peng, H. J.; Chang, Z.N.; Tsai, L.C.; Su, S.N.; Shen, H.D.; Chang C.H. Heat denaturation of

528

egg-white proteins abrogates the induction of oral tolerance of specific Th2 immune

529

responses in mice. Scand J Immunol. 1998, 48, 491-496.

530 531

32.Joo, K.; Kato, Y. Assessment of allergenic activity of a heat-coagulated ovalbumin after in vivo digestion. Biosci. Biotech. Bioch. 2006, 70, 591–597.

532

33.Roth-Walter, F.; Berin, M. C.; Arnaboldi, P.; Escalante, C. R.; Dahan, S.; Rauch, J.; Jensen-

533

Jarolim, E.; Mayer, L. Pasteurization of milk proteins promotes allergic sensitization by

534

enhancing uptake through Peyer's patches. Allergy, 2008, 63, 882-890.

535

34.Golias, J.; Schwarzer, M.; Wallner, M.; Kverka, M.; Kozakova, H.; Srutkova, D.; Klimesova

536

K.; Sotkovsky, P.; Palova-Jelinkova, L.; Ferreira, F.; Tuckova, L. Heat-induced structural

537

changes affect OVA- antigen processing and reduce allergic response in mouse model of

538

food allergy. PLoS One, 2012, 7, e37156.

539

35.Claude, M.; Lupi, R.; Bouchaud, G.; Bodinier, M.; Brossard, C.; Denery-Papini, S. The

540

thermal aggregation of ovalbumin as large particles decreases its allergenicity for egg

541

allergic patients and in a murine model. Food Chem. 2016, 203, 136-144.

542

36.Gieni, R. S.; Yang, X.; Kelso, A.; Hayglass, K. T. Limiting dilution analysis of CD4 T-cell

543

cytokine production in mice administered native versus polymerized ovalbumin: directed

544

induction of T-helper type-1-like activation. Immunology, 1996, 87, 119–126.

545

37.Rupa, P.; Schnarr, L.; Mine, Y. Effect of heat denaturation of egg white proteins ovalbumin

546

and ovomucoid on CD4+ T cell cytokine production and human mast cell histamine

547

production. J. Funct. Foods, 2015, 18, 28-34.

548 549 550 551

38.Finkelman, F. D. Anaphylaxis: Lessons from mouse models. J. Allergy Clin. Immunol. 2007, 120, 506-515. 39.Finkelman, F. D.; Khodoun, M. V.; Strait, R. Human IgE-independent systemic anaphylaxis. J. Allergy Clin. Immunol., 2016, 137, 1674-1680. 21 ACS Paragon Plus Environment

Journal of Agricultural and Food Chemistry

552 553 554 555

Page 22 of 32

40.Mestas, J.; Hughes, C. C. W. Of mice and not men: Differences between mouse and human immunology. J. Immunol. 2004, 172, 2731-2738. 41.Shin, M.; Han, Y.; Ahn, K. The influence of the time and temperature of heat treatment on the allergenicity of egg white proteins. Allergy Asthma Immunol. Res. 2013, 5, 96–101.

556

42.Meersman, F.; Atilgan, C.; Miles, A. J.; Bader, R.; Shang, W.; Matagne, A.; Wallace, B. A.;

557

Koch, M. H. J. Consistent picture of the reversible thermal unfolding of hen egg-white

558

lysozyme from experiment and molecular dynamics. Biophys J. 2010, 99, 2255–2263.

559

43.So, T.; Ito, H.; Hirata, M.; Ueda, T.; Imoto, T. (2001). Contribution of conformational

560

stability of hen lysozyme to induction of type 2 T-helper immune responses. Immunology,

561

2001, 104, 259-268.

562

44.Peters, N. C.; Hamilton, D. H.; Bretscher, P. Analysis of cytokine-producing Th cells from

563

hen egg lysozyme-immunized mice reveals large numbers specific for "cryptic" peptides and

564

different repertoires among different Th populations. Allergy, 2011, 41, 20–28.

22 ACS Paragon Plus Environment

Page 23 of 32

Journal of Agricultural and Food Chemistry

565

Funding: This work was supported by MINECO (project AGL2014-59771R and contract of

566

A.P-T), and MECD (through D.L-O contract).

567 568 569

Abbreviations used: CD, circular dichroism; CT, cholera toxin; EW, egg white; HEW,

570

heated egg white; i.p.., intraperitoneal; LYS, lysozyme; MCP-1, mast cell protease-1; OVA,

571

ovalbumin; OM, ovomucoid; PCA, passive cutaneous anaphylaxis; PEW, pressurized egg

572

white

23 ACS Paragon Plus Environment

Journal of Agricultural and Food Chemistry

Page 24 of 32

Table 1. Protein- specific IgE (ng/ml) and IgG1 (µg/ml) levels in the sera of mice sensitized to EW, HEW or PEW measured at 8th week (before challenge) by indirect ELISA. Naïve mice were used as controls. Data are expressed as means ± SEM (n= 5).

IgE (ng/ml)

IgG1 (µg/ml)

Sensitization group

Protein-specific Immunoglobulin

A-C a-c

EW HEW PEW Naïve EW HEW PEW Naïve

EW

OVA

OM

LYS

AB 1248.5 b ±216.7

AB 1407.7 b ±272.3

A 2121.9 a ±362.9

B 517.4 b ±62.9

A 2835.6 a ±316.0

A 3031.6 a ±309.7

A 2839.5 a ±588.3

B 38.0 c ±33.8

AB 1910.6 ab ±275.9

AB 1903.9 b ±318.8

A 2906.2 a ±439.1

B 958.0 a ±191.4

0.0 c ±0.0

0.0 c ±0.0

0.0 b ±0.0

0.0 c ±0.0

A 554.1 a ±45.4

B 276.0 a ±37.4

B 191.8 a ±34.7

B 314.6 a ±18.1

A 69.1 b ±9.5

A 76.3 b ±8.2

B 36.9 b ±10.2

C 1.8 b ±0.1

A 643.9 a ±50.8

B 371.9 a ±53.5

B 221.5 a ±48.1

B 364.9 a ±29.5

2.3 b ±0.6

2.5 b ±0.2

1.8 b ±0.1

1.7 b ±0.2

HEW

PEW

A 3674.8 a ±558.9 AB

0.0 b ±0.0 A 77.5 a

1901.0 a ±298.2 0.0 b ±0.0

±16.1 A 694.5 a ±75.5

1.3 b ±0.1

1.7 b ±0.2

Different uppercase superscript letters indicate significant differences (P< 0.05) within rows.

Different lowercase superscript letters indicate significant differences (P< 0.05) within columns for each antibody (IgE, IgG1).

24

ACS Paragon Plus Environment

Page 25 of 32

Journal of Agricultural and Food Chemistry

Figure captions Figure 1. SDS-PAGE patterns of EW, HEW and PEW, without and with β-mercaptoethanol (-βME and + β-ME respectively) (a). In vitro gastric (G, 20 and 60 min) and gastrointestinal (GI, 20 and 60 min) digests of EW, HEW and PEW with β-mercaptoethanol (b). MW: molecular weight marker; OVT: ovotransferrin; OVA: ovalbumin; OM: ovomucoid; LYS: lysozyme. Figure 2. Far-UV circular dichroism spectra of EW (−), HEW (--) and PEW (•••) at pH 7.0 and 20ºC. Figure 3. Body temperature (a), clinical sign scores (b), and serum concentrations of MCP-1 (c) in BALB/c mice sensitized to EW, HEW or PEW and challenged with these protein preparations. Oral challenges were followed by i.p. challenges 40 min apart. Values are expressed as means ± SEM (a, c) or medians (b). Different letters indicate statistically significant differences (P< 0.05) within orally or i.p. challenged animals (n= 5). Figure 4. Binding capacity of IgE from pooled serum samples of mice (n=5) sensitized to EW, HEW and PEW to each of these protein preparations determined by direct antibody capture ELISA (a). Competition of EW, HEW and PEW for the binding of IgE antibodies present in serum of EW- (b), HEW- (c) and PEW-sensitized mice (d) to biotin-labelled EW, HEW and PEW, respectively. Results are presented as means ± SEM and different letters indicate statistically significant differences (P< 0.05) (technical triplicates). Figure 5. Production of IFNγ, IL-4, IL-5 and IL-10 by splenocytes of mice sensitized to EW, HEW or PEW and stimulated with individual egg proteins (OVA, OM and LYS), as well as with these protein preparations. Data are expressed as means ± SEM (n= 5). Different lowercase letters indicate statistically significant differences (P< 0.05) within each sensitized group and different uppercase letters indicate statistically significant differences (P< 0.05) among different sensitization groups for the same stimulus.

25 ACS Paragon Plus Environment

Journal of Agricultural and Food Chemistry

Page 26 of 32

Supplementary Figure 1. Levels of IgE and IgG1 specific for EW, OVA, OM and LYS in sera from mice sensitized to EW (a), HEW (b), and PEW (c) at different days throughout the sensitization period determined by indirect ELISA. Data are expressed as means ± SEM (n=5). Supplementary Figure 2. Passive cutaneous anaphylaxis assay with unheated and heated pooled sera (n= 5) from HEW -sensitized mice. Data are expressed as means ± SEM (n=2). *indicates statistically significant differences between the responses induced by heated and non-heated sera (P< 0.05).

26 ACS Paragon Plus Environment

Page 27 of 32

Journal of Agricultural and Food Chemistry

TOC Graphic

ACS Paragon Plus Environment

Journal of Agricultural and Food Chemistry

Page 28 of 32

FIGURE 1 a)

b) - β-ME

EW

+ β-ME

MW EW HEW PEW EW HEW PEW

HEW

PEW

MW G20´ G60´ GI20´ GI60´ G20´ G60´ GI20´ GI60´ G20´ G60´ GI20´ GI60´

kDa 250 150 100 75

kDa 250 150 100 75

50

50

37

OVA 37

OVT

OM

25 20

25 20

15

15

10

10

LYS

ACS Paragon Plus Environment

Page 29 of 32

Journal of Agricultural and Food Chemistry

Ɵ (deg·cm2·cg-1)

FIGURE 2 2500 0 -2500 -5000 200

210

220

230

240

250

l (nm)

ACS Paragon Plus Environment

Journal of Agricultural and Food Chemistry

Page 30 of 32

FIGURE 3 Oral

a)

Temperature (ºC)

40

ab

a

38

i.p. a

a

ab a

b

b

b

ab

abc

a

a bc c

bc

36 34 32

EW Sensitization Challenge EW HEW PEW

HEW

PEW

EW HEW

EW PEW

Naïve

EW

HEW

PEW

EW HEW PEW

EW HEW

EW PEW

a

a

a

Naïve

b)

Clinical signs score

5

ab

4

ab

a

a

a ab

ab

3

b

bc 2

cd

c

1

d

c

0

Sensitization EW Challenge EW HEW PEW

HEW

PEW

EW HEW

EW PEW

EW

HEW

PEW

EW HEW PEW

EW HEW

EW PEW

Naïve

a

c)

MCP-1 pg/ml

30000

a

a

20000 ab

ab

10000

b 0 Sensitization Challenge

EW EW HEW PEW

b b HEW

PEW

EW HEW

EW PEW

ACS Paragon Plus Environment

Naïve

Naïve

Page 31 of 32

Journal of Agricultural and Food Chemistry

FIGURE 4 IgE 1.0 a

0.8

ab

0.6 b

0.4 0.2 0.0

c)

100

100

80

80 % B/B0

% B/B0

b)

EW

60 40

HEW

PEW

d)

60 40

REW 20 100

100

%B/B 0

80

2

4

6

0

Log10 [non-labelled protein]

60 40

40 20

2

4

6 EW Log10 [non-labelled protein] EW HEW EW HEW PEW HEW PEW PEW

20 0 0 2 4 Log10 [non-labelled protein] 0 2 4 6 Log10 [non-labelled protein] 2 4 6 Log10 [non-labelled protein]

0

40

REW

80 0

60

60

20

20

REW

100 80

% B/B0

Absorbance units (450 nm)

a)

6

ACS Paragon Plus Environment

0

2

4

6

Log10 [non-labelled protein]

Journal of Agricultural and Food Chemistry

Page 32 of 32

FIGURE 5

IFN  (ng/mL)

20.0 15.0 10.0 5.0

B B B a a a B B B b b b

A A A a a a A A A b b b

B B a B ab B B b B cd c d

0 A a

1.5 IL 4 (ng/mL)

a AB a

1.0 0.5

a B ab ab

a a

B AB b b b

B ab

a

A b A c c

B ab

0

A A a A ab ab

IL 5 (ng/mL)

1.5 1.0 0.5

B B B B a a a B b b b

AB bc AB c c

B B B ab ab a

A bc c

A c

0 A

a

IL 10 (ng/mL)

6 4 2

B bc B B c c

B B B a ab a

B ab

B B B a a ab

A a

A b

A a

A A b b

B B b b

0

ACS Paragon Plus Environment

PEW

HEW

EW

LYS

OM

OVA

PEW

PEW HEW

EW

LYS

OM

OVA

PEW

HEW

EW

LYS

OM

OVA

Cell stimulus

HEW

EW

Sensitization