In vitro killing of Ehrlichia risticii by activated and immune mouse peritoneal macrophages.

Normal resident murine peritoneal macrophages inoculated in vitro with Ehrlichia risticii readily phagocytized the organism but were unable to suppress ehrlichial replication as determined by indirect fluorescent-antibody staining of the inoculated cells. In contrast, macrophages from Corynebacterium parvum-inoculated and E. risticii-recovered mice rapidly eliminated the ehrlichiae. Macrophages from E. risticii-recovered mice were as effective as the C. parvum-activated cells in phagocytizing and eliminating the organism. Opsonization of E. risticii with homologous antiserum prior to inoculation of macrophage cultures resulted in enhancement of phagocytosis and greater suppression of E. risticii replication in all macrophage groups. These findings indicate that the pathogenesis of E. risticii infection centers on the ability of the organism to enter and replicate within the macrophage with avoidance of macrophage antimicrobial effects. An immune response results in macrophage activation with enhancement of the macrophage's ability to eliminate E. risticii. Opsonization of E. risticii with anti-E. risticii serum renders E. risticii more susceptible to macrophage destruction.