CD4(+) AND CD8(+) T-CELL-DEPENDENT AND T-CELL-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 primacy and secondary tularemia can be mediated by cells other than CD4(+) and CD8(+) T cells.