Macrophages in resistance to rickettsial infection: strains of mice susceptible to the lethal effects of Rickettsia akari show defective macrophage Rickettsicidal activity in vitro

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Abstract
Activation of macrophages was assessed in strains of mice inoculated intraperitoneally with 1,000 times the 50% lethal dose of Rickettsia akari. Macrophages from mice resistant to R. akari infection (C3H/HeN, C57BL/10J, and BALB/cN) were nonspecifically tumoricidal 2 to 4 days after rickettsial inoculation. Moreover, these macrophages were microbial for R. akari in vitro; cells were resistant to infection with the bacterium and were capable of killing intracellular rickettsiae. In contrast, macrophages from strains of mice susceptible to R. akari (C3H/HeJ, C57BL/10SnCR, and A/J) failed to develop nonspecific tumoricidal activity over the course of lethal disease and became infected with R. akari in vivo within 2 days of rickettsial inoculation. Macrophages from uninfected mice of strains susceptible to R. akari also could not be activated for rickettsicidal or tumoricidal activities by treatment with macrophage-activating agents (Mycobacterium bovis BCG) in vivo or by treatment with lymphokines in vitro.