Comparison of specificity between IgG, IgE and T cells to three casein components: Implication for the role of circulating allergenspecific T cells in food allergy

In order to investigate the role of food antigen-specific T cells circulating in the blood of patients with food allergy, we compared T cell response to three casein components (αs-, β- and, K-casein) with specificities of IgG and IgE binding to the casein components in four milk-allergic patients (P1-4) with atopic dermatitis. In all patients, the binding activities of IgG antibodies to αs-casein were most dominant, followed by those to β- and to K-casein. The major component of casein bound by IgE antibodies was αs-casein in P1 and P3, K-casein in P2, and αs-casein as well as K-casein in P4; the order of casein components bound by IgE antibodies was different from that by IgG antibodies. Proliferative responses of peripheral blood mononuclear cells (PBMC) to casein components were so low that the dominance of casein recognition could not be clearly demonstrated. However, short-term T cell lines that specifically respond to casein were successfully established from PBMC of the four patients and the proliferative responses of the T cell lines to the three components of casein were in accord with the IgE antibody specificity to casein components but not with that of IgG antibody specificity. When taken together, these results indicate that casein-specific T cells circulating in the blood are involved in or reflect an allergic reaction against casein.