Characterization of a fetal calf serum-derived molecule reactive with human natural antibodies: its occurrence in tissue culture-grown type C RNA viruses.

By means of a sensitive radioimmunoprecipitation (RIP) assay, simian sarcoma virus-simian sarcoma-associated virus (SSV-SSAV), purified from culture fluids of infected normal rat kidney (NRK) cells, was shown to acquire a surface antigen from serum used in the tissue culture medium. This antigen, which was acquired when serum from either fetal calf, horse, swine, rabbit, or chicken origin was used, accounted for a substantial portion (but not all) of the total precipitating activity exhibited by natural human antibodies for membrane-associated antigens of these viruses. By 1) alcohol precipitation, concanavalin A chromatography, and Sephadex G-150 filtration of fetal calf serum (FCS) proteins or 2) chromatography of serum proteins over a human IgG-containing immunoaffinity column, a glycoprotein of approximately 55,000 daltons has been identified which is a minor constituent of FCS (less than 0.1% of total protein) and has the antigenic capacity of whole FCS.