ROLE OF T-LYMPHOCYTE SUBSETS IN IMMUNITY TO SPOTTED-FEVER GROUP RICKETTSIAE

To evaluate the roles of CD4 and CD8 T lymphocytes in immunity to diss eminated endothelial infection with Rickettsia conorii (Malish 7 strai n), these T cell subsets were depleted or adoptively transferred into subsequently infected C3H/HeN mice. CD4 T lymphocyte-depleted and sham -depleted mice underwent a similar course of illness with a sublethal rickettsial dose, cleared the infection by day 10, and recovered on da ys 10 to 11. In contrast, mice depleted of CD8 lymphocytes or CD4 and CD8 lymphocytes died or remained persistently infected through day 15 with the ordinarily sublethal dose. Endothelium was the major site of rickettsial persistence, including sites in the vital organs, brain, a nd lungs of CD8 lymphocyte-depleted mice. In nondepleted animals, CD8 T lymphocytes were observed in apposition to endothelial cells on day 10 at the time of rickettsial clearance. Adoptive transfer of immune C D4 or CD8 T lymphocytes protected mice against a lethal dose of R. con orii in the disseminated endothelial target model. Nonimmune CD4 or CD 8 lymphocytes and immune lymphocytes that had passed through columns t hat depleted both CD4 and CD8 lymphocytes failed to protect mice again st R. conorii. These studies represent the first analysis of the role of T lymphocyte subsets in immunity to spotted fever group rickettsiae and the first demonstration that clearance of spotted fever group ric kettsiae from endothelial cells requires immune CD8 T lymphocytes.