Sub-class of IgG in allergic disease I. IgG sub-class antibodies in immediate and non-immediate food allergy

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Abstract
Previous studies have suggested that, apart from IgE‐mediated reactions, some of the symptoms of food allergy may be caused by IgG antibodies to food proteins. This study was carried out to see if there were any distinctive features of the IgG sub‐class antibody response to dietary antigens which occurs in food allergic patients. IgG subclass antibodies were measured using a quantitative enzyme‐linked immuno‐sorbent assay (ELISA) to wheat gliadin, ovalbumin and bovine casein in twenty patients who had coeliac disease and in twenty‐eight egg allergic patients. These were compared with twenty‐one atopic dermatitis patients who did not have food allergy and twenty‐six healthy control subjects. Coeliac disease patients tended to have raised IgG antibody levels (especially IgG1) to all three antigens but these overlapped considerably with that seen in egg allergic and atopic dermatitis patients. Coeliacs who avoided gluten had anti‐gliadin antibody levels which did not differ from those seen in healthy subjects but nevertheless had raised anti‐ovalbumin and casein‐specific antibodies. The IgG antibody was largely restricted to IgG1 and IgG4 sub‐class although the relative amount of each varied with the antigen. Although gliadin‐specific antibodies were mainly IgG1, ovalbumin‐specific antibodies were mainly IgG4. The increased antibody levels to all three antigens in coeliacs were caused by a raised IgG1 response, IgG4 antibodies were usually normal. Egg allergic patients also had raised IgG1 but not IgG4 antibodies to ovalbumin. These data show that the response to different dietary antigens can vary with the antigen. The fact that IgG1 and not IgG4antibodies were raised to all three antigens in patients with coeliac disease suggests that they are a secondary consequence of the disease, perhaps reflecting increased transport of antigens across a damaged gut mucosa rather than a specific immunopathological reaction. However, the observation that antibodies to gliadin, and not ovalbumin or casein, fell following gluten avoidance shows that the response to gliadin, at least, is dependent upon continued exposure to antigen.