IgG subclass of human serum antibodies reactive with dietary proteins.

Serum IgG antibodies reactive with different dietary proteins have been detected in a significant proportion of adult patients with coeliac disease, dermatitis herpetiformis and atopic eczema. Serum anti-milk antibodies were shown to be distributed predominantly between the IgG2 and IgG4 subclasses, whereas anti-gliadin antibodies in atopic eczema were predominantly of the IgG4 subclass. Furthermore, as antibodies to each of these dietary antigens in healthy adults were markedly restricted to the IgG4 subclass, their production may be part of a normal immune response to dietary proteins. There was no correlation between serum IgG4 antibody and total serum IgG4 level. In contrast, restricted IgG4 anti-gliadin antibodies were less prevalent in the serum of patients with coeliac disease and dermatitis herpetiformis, suggesting defective downstream switching of Ig heavy-chain genes in these conditions.