CD8A and infection: In case of the infection with SFG (R. rickettsii, R. conorii), transitional rickettsiae (R. australis), and O. tsutsugamushi, CD8+ T cells seem to be indispensable for defense as reflected by the observations that CD8+ T cell-deficient or depleted mice show reduced survival, enhanced bacterial burden and pathology in the infection with R. conorii, R. australis and O. tsutsugamushi [48,51,52,53].