HELPER T-CELL SUBSETS FOR IMMUNOGLOBULIN-A RESPONSES - ORAL IMMUNIZATION WITH TETANUS TOXOID AND CHOLERA-TOXIN AS ADJUVANT SELECTIVELY INDUCES TH2 CELLS IN MUCOSA-ASSOCIATED TISSUES

Antigen-specific B cell responses to mucosally delivered proteins are dependent upon CD4-positive T helper (Th) cells, and the frequency of Th1 and Th2 cell responses after oral immunization may determine the l evel and isotype of mucosal antibody responses. We have used a protein -based vaccine, tetanus toxoid (TT), together with the mucosal adjuvan t cholera toxin (CT), for oral immunization of mice to study the natur e of antigen-specific Th cell subsets induced in Peyer's patches (PP) of the gastrointestinal (GI) tract and in the spleen (SP) during peak antibody responses. Mice orally immunized with TT and CT responded wit h antigen-specific secretory immunoglobulin A (S-IgA) antibodies in th e GI tract, and with both IgG and IgA antibody responses in serum. PP and SP CD4+ T cells from mice orally immunized with TT plus CT were cu ltured with antigen-coated latex microspheres for induction of prolife rative responses and for enumeration of cytokine producing CD4+ T cell s. Interestingly, both PP and SP CD4+ T cell cultures showed increased numbers of IL-4- and IL-5 (Th2-type)-producing, spot-forming cells (S FCs) after 21 d of immunization, while essentially no interferon-gamma (IFN-gamma) or IL-2 (Th1-type) SFCs were noted. Cytokine-specific Nor thern blots and RT-PCR also revealed that significant IL-4 and IL-5 mR NA levels, but not IFN-gamma or IL-2 mRNA, were present in CD4+ T cell s isolated from antigen-stimulated cultures. However, systemic immuniz ation with TT and CT induced antigen-specific IgG and IgM but not IgA antibodies in serum. Further, both IL-2- and IFN-gamma-producing Th1-t ype cells as well as IL-4- and IL-5-secreting Th2-type cells were gene rated in SP. Our results show that oral immunization with TT and the m ucosal adjuvant CT selectively induced antigen-specific Th2-type respo nses which may represent the major helper cell phenotype involved in m ucosal IgA responses in the GI tract.