The influence of dietary protein antigen on Th1/Th2 balance and cellular immunity.

Dietary administration of ovalbumin (OVA) antigen (Ag) into OVA-specific T cell receptor alphabeta-transgenic (TCR-Tg) mice resulted in the induction of activated CD4+ Th cells expressing CD69 early activation Ag. However, the number of CD4+ Th cells rather decreased by dietary administration of OVA antigen. The production of Th1-cytokines such as IFN-gamma and IL-2 markedly reduced in spleen of OVA-fed mice compared to mice fed with normal diet. In sharp contrast, the production of Th2-cytokine, IL-4 greatly increased in spleen of OVA-fed mice though the number of CD4+ T cells decreased to less than 10% of control mouse spleen. The decrease of IFN-gamma production and the increase of IL-4 production by CD4+ T cells was demonstrated at a single cell level by intracellular cytokine staining analysis. Moreover, such a polarized cytokine production pattern was also demonstrated using highly purified CD4+ T cells obtained from mice fed with OVA. In addition to the decrease of Th1-cytokine production, TCR-Tg mice fed with OVA-containing diet showed greatly reduced in vivo generation of NK cells, LAK cells and CTL. These results suggested that dietary protein antigen caused the polarization of Th1/Th2 balance into Th2-dominant immunity and inhibited cellular immunity.