Rickettsial infection in murine models activates an early anti-rickettsialeffect mediated by NK cells and associated with production of gamma interferon

Natural killer (NK) cell activity was significantly increased on days 2-6 o f infection in the Rickettsia conorii-infected C3H/HeN mice and on day 2 in the Rickettsia typhi-infected C57BL/6 mice. Depiction of NK cell activity utilizing anti-NK1.1 monoclonal antibody enhanced the susceptibility of nor mally resistant C57BL/6 mice to infection with R. typhi, and depletion of N K cell activity with antibody to asialo GM(1) enhanced the susceptibility o f C3H/HeN mice to infection with R. conorii. Serum gamma interferon was inc reased in R. conorii-infected C3H/HeN mice compared with NK cell-depleted, infected mice during the early course of infection. Additionally, the NK ce ll activating cytokine IL-12 was elevated in the sera of infected mice duri ng the time period representing enhanced NK cell activity compared with uni nfected mice. Thus, it appears that NK cells contribute to the early anti-r ickettsial immune response, likely via a mechanism involving gamma interfer on.