Jerry R. McGhee

Streptococcus mutans and Vibrio cholerae, but not Escherichia coli, were killed by incubation with purified human apolactoferrin. Concentrations of lactoferrin below that necessary for total inhibition resulted in a marked reduction in viable colony-forming units. This bactericidal effect was contingent upon the metal-chelating properties of the lactoferrin molecule.

Freshly isolated murine PP B cells were cultured with 10 different cytokines, including IL-1 alpha, IL-2, IL-4, IL-5, IL-6, IL-7, IFN-gamma, TNF-alpha, and TGF-beta, to investigate a possible role for these cytokines in induction of Ig synthesis. Of interest was the finding that only IL-5 and both mouse recombinant (mr) and human recombinant (hr) IL-6 enhanced IgA synthesis. The effect was greater with either mrIL-6 or hrIL-6 than with mrIL-5. IL-6 induced cycling mIgA+ PP B cells to secrete high levels of IgA (approximately 7-fold increase over control). Of importance was the finding that mrIL-6 had little effect on secretion of IgM or IgG by PP B cell cultures. hrIL-6 also increased IgA secretion by PP B cells and this enhancement was abolished by a goat anti-hrIL-6 antiserum. mrIL-6 did not cause B cell proliferation but induced a sharp increase in numbers of B cells secreting IgA. Isotype-switching was not a mechanism for this marked increase in IgA synthesis since mIgA- PP B cells were not induced to secrete IgA by mrIL-6. From these studies we conclude that IL-6 plays an important role in promoting the terminal differentiation of PP B cells to IgA-secreting plasma cells.

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 level and isotype of mucosal antibody responses. We have used a protein-based vaccine, tetanus toxoid (TT), together with the mucosal adjuvant cholera toxin (CT), for oral immunization of mice to study the nature 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 with antigen-specific secretory immunoglobulin A (S-IgA) antibodies in the 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 cultured with antigen-coated latex microspheres for induction of proliferative responses and for enumeration of cytokine producing CD4+ T cells. Interestingly, both PP and SP CD4+ T cell cultures showed increased numbers of IL-4- and IL-5 (Th2-type)-producing, spot-forming cells (SFCs) after 21 d of immunization, while essentially no interferon-gamma (IFN-gamma) or IL-2 (Th1-type) SFCs were noted. Cytokine-specific Northern blots and RT-PCR also revealed that significant IL-4 and IL-5 mRNA levels, but not IFN-gamma or IL-2 mRNA, were present in CD4+ T cells isolated from antigen-stimulated cultures. However, systemic immunization 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-type cells as well as IL-4- and IL-5-secreting Th2-type cells were generated in SP. Our results show that oral immunization with TT and the mucosal adjuvant CT selectively induced antigen-specific Th2-type responses which may represent the major helper cell phenotype involved in mucosal IgA responses in the GI tract.