Search for endogenous C-type viruses in cultures of non leukemic human cells

Cultures of cells derived from non-leukemic human tissues were submitted to treatments known to induce endogenous C-type viruses of a number of animal species. Virus expression was evaluated by reverse transcriptase (RT) assays in the growth medium. Of 20 cultures treated or untreated with bromodeoxyuridine, 18 were totally negative in RT assays. Of the 2 positive cultures, one was a human-mouse hybrid in which the induction of RT activity coincided with the expression of murine antigens. The other culture, a diploid strain which exhibited borderline enzymatic activity, was subjected to more detailed analysis after treatment with several chemical inducers and/or irradiation, but none of these procedures gave clearly positive results. The apparent lack of an endogenous virus synthesis in these human cells is discussed.