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The production of interferon or interferon-like inhibitors has been induced by practically every major viral group and by non-viral substances including bacteria, bacterial endotoxins, statolon, phytohaemagglutinins, and the nucleic acids and their derivatives (Ho et al. 1966). Although in vivo induction of an interferon-like inhibitor by Coxiella burneti and Rickettsia prowazeki has been demonstrated by Kazar (1966), the only rickettsial agent reported to induce the production of interferon in cell culture is R. tsutsugamushi (Hopps et al. 1964). The present communication describes the selective induction of interferon in cell cultures by another rickettsia, C. burneti.
A partially purified suspension of the ad (California bovine) strain of Coxiella burneti containing 1 × 106 cell-infecting units/ml., prepared and assayed in accord with procedures described previously (Hahon & Cooke, 1966), was employed for induction of interferon in L cells and McCoy (human origin) cell cultures. Nutrient medium for both cell lines consisted of medium 199 with 0.5% lactalbumin hydrolysate and 10% calf serum.