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.
Fifty-six adult patients with atopic eczema have been evaluated for serum antibodies reactive with wheat gliadin, bovine milk or chicken ovalbumin using a solid-phase enzyme-linked immunoassay (ELISA). Of the atopic eczema sera 357% were positive against gliadin and/or milk, compared with 92% of the control adult blood donor sera (P< 0-0005). In particular, 304% of atopic eczema patients had detectable IgG antibodies reactive with gliadin in contrast to 65% of the controls (P < 0-0005). These findings suggest that antigen absorption from the gut may play a role in the aetiopathogenesis of atopic eczema, and lend some support for the use of elimination diets in this condition.Atopic eczema affects about 3% of children under the age of 5 years and spontaneously resolves in the majority by the late teens. However, eczema may persist, reappear, or can appear for the first time in adult life and the pathogenesis of this disorder remains unclear. Affected individuals typically have elevated serum IgE levels and IgE antibodies against a range of inhalent and dietary antigens (Johnson et al., 1974;Wraith et al., 1979;Barnetson, Merrett & Ferguson, 1981). It is likely that IgE-mediated hypersensitivity reactions can be incriminated in other atopic manifestations such as asthma and hay fever, whereas the skin lesions involve infiltration into the epidermis of mononuclear cells, principally lymphocytes and monocytes/macrophages (Mihm et al., 1976). It is thus difficult to ascribe the aetiopathogenesis of these skin lesions to an IgE-mediated immunological reaction.Investigation of a large series of adult male and female blood donors has shown 13-4% of this normal population to have detectable serum IgG, IgA or IgM (IgG/A/M) antibodies reactive in Correspondence: Dr R.M.R
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