Georgia Journal of Science


Rickettsia prowazekii, the bacterium that causes epidemic typhus, mainly grows within endothelial cells and can also infect macrophages. Previous studies showed that pretreatment of cultured, murine macrophage-like RAW264.7 cells with gamma interferon, followed by R. prowazekii infection, leads to the death of many of the macrophages within several hours after infection. The present study examined the fate of the rickettsiae after macrophage death. Rickettsiae released from gamma interferon-pretreated, infected macrophage cultures, in which 83 ± 4% (mean ± standard deviation) of the macrophages were trypan blue-positive (dead), remained viable, as judged by their ability to infect and grow in untreated Vero cells (originally established from the kidney of an African green monkey). The growth of these rickettsiae was comparable to the growth of rickettsiae released from untreated, infected macrophage cultures, in which 1 ± 1% of the macrophages were trypan blue-positive. These data raise the possibility that gamma interferon, which is known to be an anti-rickettsial host defense, may, in some instances, contribute to the spread of R. prowazekii infection within a host.