Cutting edge:: Role of B lymphocytes in protective immunity against Salmonella typhimurium infection

Infection of mice with Salmonella typhimurium gives rise to a disease similar to human typhoid fever caused by S. typhi, Since S. typhimurium is a facultative intracellular bacterium, the requirement of B cells in the immune response against S. typhimurium is a longstanding matter of debate. By infecting mice on a susceptible background and deficient in B cells (Ig mu(-/-) mice) with different strains of S, typhimurium, we could for the first time formally clarify the role of B cells in the response against S. typhimurium. Compared with Ig mu(+/+) mice, LD,, values in Ig mu(-/-) mice were reduced during primary, and particularly secondary, oral infection with virulent S, typhimurium. After systemic infection, Ig mu(-/-) mice cleared attenuated aroA(-) S. typhimurium, but vaccine-induced protection against systemic infection with virulent S. typhimurium involved both B cell-dependent and -independent effector mechanisms. Thus, B cell-mediated immunity plays a distinct role in control of S. typhimurium in susceptible mice.