Immunological Mechanisms of Food Allergy

Abstract

Food allergy is thought to be caused mainly by the reaction of IgE antibody to food antigens. Immunoglobulin class switch to IgE is induced by the transcription of germ line transcript from I region and splicing of S region present in upstream of the gene of IgE constant region. These reactions are triggered by the stimuli to IL-4 receptors and CD 40 molecules on B cells and suppressed by the action of interferon-γ. Therefore, balance between Th 2 cells producing IL-4 and Th 1 cells producing interferon-γ is important for IgE production and the factors providing Th 2 dominancy are related to the occurrence of allergy. The mucosal immune system is somehow independent from general immune system and there present many T cells producing TGF-β or IL-10 in the gut associated lymphoid tissues. TGF-β induces class switch to IgA and therefore provides the condition to produce secretory IgA antibodies. In contrast, IL-10 suppresses Th 1 cells and therefore provides the condition to produce IgE. Unmethylated CpG motif of bacterial DNA causes IL-12 production from macrophages and IL-12 induce Th 1 cells. Thus activated Th 1 cell would suppress IgE production. The development of food allergy seems to be controlled by the two opposing conditions namely the presence of antigens or other substances which induce Th 2 reaction and by the presence of the substances such as bacterial DNA which induce Th 1 reaction.