Cell generation and type C virus expression in the human embryonic cell strain HEL-12

The spontaneous expression of a type C virus in a diploid strain of human embryonic lung fibroblast-like cells (HEL-12) was examined during serial culture. Virus antigen expression was determined by indirect immunofluorescenc with antisera to disrupted simian sarcoma virus and the 28000 mol. wt. internal antigen of the endogenous cat virus RD-114. Virus production was examined by reverse transcriptase assays of culture fluids. Virus antigens were not detected for 25 days after frozen, primary HEL-12 cells were reinstated in culture. The cells expressed virus antigens but did not release virus particles between 25 and 80 days. Spontaneous virus release and maximal antigen expression occurred in cells grown for 80 to 120 days. Virus particles were not detected after 120 days although virus antigens persisted until the experiment was terminated. The HEL-12 virus was infectious for cell cultures of human, rhesus monkey, dog and rabbit cells. The proportion of SiSV-like and RD-114-like antigenic components of HEL-12 virus were altered by passage through heterologous cells suggesting heterogeneity of the HEL-12 virus population.