Interferonlike factors from antigen- and mitogen-stimulated human leukocytes with antirickettsial and cytolytic actions on Rickettsia prowazekii. Infected human endothelial cells, fibroblasts, and macrophages.

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Abstract
Cultures of human blood leukocytes, upon immunologically specific stimulation with R. prowazekii antigen or nonspecific stimulation with the mitogen phytohemogglutinin, produce soluble factor(s) in the supernatant fluid which, in culture, have an intracellular antirickettsial action on R. prowazekii-infected human endothelial cells, fibroblasts and macrophages, and a specific cytolytic action on R. prowazekii-infected, but not uninfected bystander, human fibroblasts. Neither action is demonstrable in R. prowazekii-infected chicken embryo fibroblasts. The factor(s) has no direct antimicrobial action on extracellular rickettsiae and is inactivated by heating at 56.degree. C for 1 h or by acid treatment at pH 2. Expression of the antirickettsial action requires new host cell messenger transcription and protein synthesis; the cytolytic action does not. The circumstances of production and action and the properties of the factor(s) responsible for the intracellular antirickettsial, and perhaps also the cytolytic action are consistent with those of immune interferon (IFN-.gamma.).