title: Comparison of properties of virulent, avirulent, and interferon-resistant Rickettsia prowazekii strains.
abstract: Several properties of virulent, avirulent, and interferon-resistant Rickettsia prowazekii strains were compared. All of the interferon-resistant rickettsial strains (which were derived from the avirulent Madrid E strain) resembled the virulent Breinl strain in that they grew well in untreated mouse macrophagelike RAW264.7 cells. In contrast, the avirulent Madrid E strain grew poorly in untreated RAW264.7 cells. Pretreatment of interferon-resistant rickettsiae or R. prowazekii Breinl with antirickettsial serum or immunoglobulin G suppressed the ability of the rickettsiae to grow in untreated RAW264.7 cells. Interferon-resistant R. prowazekii strains, like the Madrid E and Breinl strains, rapidly killed a substantial proportion of RAW264.7 cells that had been treated with gamma interferon or very high concentrations of alpha/beta interferon. Untreated infected RAW264.7 cells and interferon-treated mock-infected RAW264.7 cells were not killed during the same period. In cultures of RAW264.7 cells treated with either alpha/beta interferon (120 to 1,200 U/ml) or a subsaturating concentration of gamma interferon (0.5 U/ml), R. prowazekii Breinl organisms killed a higher percentage of the cells than did comparable numbers of R. prowazekii Madrid E organisms or interferon-resistant rickettsiae. Although R. prowazekii Breinl (like R. prowazekii Madrid E) was quite sensitive to gamma interferon in mouse L929 cells, the Breinl strain was resistant to murine alpha/beta interferon compared with the Madrid E strain and the two strains selected for resistance to murine gamma interferon. One of the interferon-resistant strains (strain 60P, which was selected for resistance to murine alpha/beta interferon) differed from the other R. prowazekii strains in that it induced little or no detectable interferon in L929 cell cultures.
authors.affiliation: Department of Microbiology and Immunology, College of Medicine, University of South Alabama, Mobile 36688.
authors.forename: J
authors.initials: J
authors.lastname: Turco
authors.forename: H H
authors.initials: HH
authors.lastname: Winkler
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D004352:Drug Resistance, Microbial; D007372:Interferons / Q000096:biosynthesis / Q000494:pharmacology*; D008264:Macrophages / Q000382:microbiology; D051379:Mice; D012283:Rickettsia prowazekii / Q000187:drug effects / Q000254:growth & development / Q000472:pathogenicity*; D014774:Virulence
chemical_list: D007372:Interferons