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Abstract

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.

Acknowledgements

ACKNOWLEDGMENTS This work was supported in part by funds from the Valdosta State University (VSU) Department of Biology, as well as grants to J.T. from the VSU Faculty Research Seed Grant Program, the VSU Graduate Faculty Scholarship Fund, and the VSU Center for Applied Research. This research was part of a thesis submitted by K.H.V. in partial fulfillment of the requirements for the Master of Science degree in Biology. We are grateful to Jonathon Audia, Archna Bhasin, and James Nienow for helpful discussions.

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