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

Infection of mice with Salmonella typhimurium gives rise to a disease simil ar to human typhoid fever caused by S. typhi, Since S. typhimurium is a fac ultative intracellular bacterium, the requirement of B cells in the immune response against S. typhimurium is a longstanding matter of debate. By infe cting mice on a susceptible background and deficient in B cells (Ig mu(-/-) mice) with different strains of S, typhimurium, we could for the first tim e formally clarify the role of B cells in the response against S. typhimuri um. Compared with Ig mu(+/+) mice, LD,, values in Ig mu(-/-) mice were redu ced during primary, and particularly secondary, oral infection with virulen t S, typhimurium. After systemic infection, Ig mu(-/-) mice cleared attenua ted 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 di stinct role in control of S. typhimurium in susceptible mice.