Antibody responses reveal differences in oral tolerance to wheatand maize grain protein fractions

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Abstract
SUMMARY: The influence of diet on humoral immune responses to gluten- and maize-derived proteins wasexamined using ELISA and protein blotting techniques. Mice raised on the maize-based (gluten-free)diet responded well to parenteral immunization with each of six gluten-derived protein preparations(whole gliadin, two omega-gliadin fractions, wheat salt-soluble proteins, a peptic-tryptic digest and asubtilisin digest of gluten), as serum antibody levels increased at least 300-fold in each case. Incontrast, mice raised on the wheat-based diet responded poorly to immunization with either wholegliadin or omega-gliadin and were virtually non-responsive to enzymic digest of gluten. Diet had littleeffect on the magnitude of the antibody response to wheat salt-soluble proteins, with both groupsshowing a 300-fold increase in titre. Similarly, tolerance to alpha-zeins, the alcohol-soluble proteinsof maize, did not occur on either diet. However, some oral tolerance was observed to maize glutelin. The specificity of the various antibody responses was then analysed by immunoblotting. Followingimmunization with gluten proteins or digests, antibodies from the maize-fed mice bound more or lessequally to each of the main gliadin bands and to the glutenins while the mice on the wheat-based diethad antibody specific for omega-gliadin proteins. Serum antibodies from the maize-fed mice, immunized with cither alpha-zein or maize glutelin, showed even labelling of the major maizeendosperm proteins while antibodies from mice on the wheat diet showed strong labelling of the M,27000 and 58000 bands. These results show that diet influenced the specificity, as well as themagnitude of serum antibody responses to cereal proteins. In addition, oral tolerance appeared toaffect the humoral response to some cereal proteins more than others. Both of these findings haveimportant implications for our understanding of coeliac disease.