Characterization and development of T-Cell immune responses in B-cell-deficient (Igh-6(-/-)) mice with Salmonella enterica serovar Typhimurium infection.

Infection of mice with Salmonella enterica serovar Typhimurium induces strong Th1 T-cell responses that are central to the control of the infection. In the present study, we examined the role of B cells in the development of Th1 T-cell responses to Salmonella by using gene-targeted B-cell-deficient mice (Igh-6(-/-) mice). The development of Th1 T-cell responses in Igh-6(-/-) mice was impaired in the early stage of a primary infection. This impairment persisted throughout the course of the disease. The ability of T cells to produce the Th1 cytokine gamma interferon and the frequency at which they did so were lower in Igh-6(-/-) mice than in control mice. We also observed a transient switch toward Th2 cytokine production in Igh-6(-/-) mice. Thus, B cells are important for the induction of protective Th1 T-cell responses in the early phase of a Salmonella infection. Activated B cells express high levels of major histocompatibility complex and costimulatory molecules and are nearly as effective as dendritic cells in their antigen-presenting cell (APC) activity. However, their importance as APCs in infection and their role in initiating and/or maintaining T-cell responses are unknown. Here, we show that B cells upregulate costimulatory molecules upon in vitro stimulation with S. enterica serovar Typhimurium and that they can present Salmonella antigens to Salmonella-specific CD4(+) T cells. Our results show that B cells are important for the development of T-cell responses in the early stage of a Salmonella infection and that this property may be due to their ability to present antigens to T cells.