Allergenicity of major cow's milk and peanut proteins determined by IgE and IgG immunoblotting

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Abstract
Background: Specific IgG antibodies are frequently observed in food‐allergic patients. However, the allergen‐fraction specificity of IgG antibodies in relation to IgE antibodies is not well defined. Our aim was to determine the IgE and IgG antibody profile to major cow's milk and peanut antigen fractions in food‐allergic patients and tolerant individuals. Methods: Sera were collected from 10 patients allergic to cow's milk and 10 patients allergic to peanuts, as well as from 20 control subjects. Cow's milk and peanut proteins were migrated on SDS–PAGE and immunoblotted for IgE, IgG, and IgG4 antibodies. Food‐specific IgE concentrations were measured by CAP System FEIA™, and IgG and IgG4 concentrations by ELISA. Results:In food‐allergic children, similar fraction‐specific IgE, IgG, and IgG4 antibody‐binding profiles to the major cow's milk or peanut antigens were found. In nonallergics, the presence of fraction‐specific IgG antibodies was mostly dependent on regular ingestion of the food. The presence of specific antibody on immunoblots correlated with their quantitative measurement. The mean value for specific IgE in cow's milk‐allergic patients was 450±1326 IU/ml, and 337±423 IU/ml in peanut allergic patients. Specific IgG antibody values in milk‐allergic patients were not different (median OD 1.5, range 0.3–2.3) from controls (median OD 1, range 0.2–1.8). However, in peanut‐allergic patients, IgG concentrations were significantly higher than in controls (OD 1.2 [0.5–1.3] vs 0.5 [0.3–0.7]; P<0.01). Conclusions: Similar fraction‐specific IgE and IgG antibody profiles in allergic individuals suggest a common switching trigger involving both isotypes. Intrinsic allergenicity might explain identical IgG antibody fraction specificity in nonallergics and in allergics. The presence of IgG antibodies in nonallergics was related to regular ingestion of the food.