The Role of B Cells in the Establishment of T Cell Response in Mice Infected with an Intracellular Bacteria, Listeria monocytogenes

To clarify the role of B cells in the establishment of T cell response against intracellular bacteria, B-cell-deficient (μMT−/−) mice were infected with an intracellular bacteria, Listeria monocytogenes, and T cell response against the bacteria was analyzed. On day 6 of primary Listeria infection, spleen T cells of the μMT−/− mice showed significantly lower levels of proliferative response and IFN-γ production than those of normal infected mice after in vitro stimulation with listerial antigen. Even in the secondary Listeria infection after immunization with viable bacteria, spleen T cells of the μMT−/− mice proliferated and produced IFN-γ against listerial antigen at significantly lower levels than those of normal immunized mice. These results demonstrate participation of B cells in priming of Listeria-specific T cells in vivo. However, B cells failed to present Listeria antigen to Listeria-specific T cells in vitro unless Listeria antigen was solubilized. Furthermore, transfer of immune serum from Listeria-infected normal mice failed to enhance the Listeria-specific T cell response of μMT−/− mice. The results indicate that B cells support the T cell response against intracellular bacteria through a mechanism other than their Ig production or antigen presentation function.