Antigenic properties of endogenous type-C viruses from spontaneously transformed clones of BALB-3T3

During long-term tissue culture of spontaneously transformed clones from BALB/c 3T3 mouse-embryo cells, some clones spontaneously begin to produce high titers of endogenous murine type-C viruses. The antigenic properties of these viruses have been analyzed by indirect immunoelectronmicroscopy and can be classified into two distinguishable populations: (a) BALB/c murine myeloma-associated extracellular viruses that carry a specific envelope antigen, xVEA, different from the typical murine leukemia viral envelope antigens; and (b) previously uncharacterized type-C viruses that have neither xVEA nor the murine leukemia viral envelope antigens. The former produces PC1 antigen and the latter might induce a new cell-surface antigen. Neither of these two populations of BALB/3T3 endogenous type-C viruses was able to infect BALB/c cells but both could infect NIH Swiss cells. A single BALB/3T3 clone, then, can release infectious endogenous type-C viruses with at least two different antigenic properties. We conclude that BALB/c somatic cells contain preexisting genetic information for production of at least closely related but, nevertheless, distinct type-C viruses.