CD4+ and CD8+ T-cell-dependent and -independent Host Defense Mechanisms Can Operate to Control and Resolve Primary and Secondary Francisella Tularensis LVS Infection in Mice

Immunity to experimental infection with the facultative intracellular bacterium Francisella tularensis is generally considered an example of T-cell-mediated, macrophage-expressed immunity. However, the results of the present study indicate that T-cell-independent mechanisms are also important in anti-Francisella defense. They show that mice selectively depleted of CD4+, CD8+, or both T-cell populations by treatment with T-cell subset-specific monoclonal antibodies remained capable of controlling and partly resolving a primary sublethal Francisella infection. Similarly, it was found that Francisella-immune mice depleted of either or both subsets of T cells retain a high degree of acquired immunity to reinfection. Together, these findings imply that resistance to primary and secondary tularemia can be mediated by cells other than CD4+ and CD8+ T cells.