Type‐C virus structural antigens on the surface of the infected cell as determined by a humoral cytotoxicity assay

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Abstract
Antisera prepared against the major structural polypeptides of Rauscher leukemia virus including gp70, p12, p30, p10 and p15 (E) were tested in a complement‐dependent cytotoxicity assay against cell lines infected with Rauscher murine leukemia virus and with the three known classes of endogenous murine leukemia viruses. gp70 antisera and p12 antisera were active in cytotoxicity showing predominantly type‐specificity to R‐MuLV3, but were shown to cross‐react in varying degrees to the three classes of endogenous type‐C virus(es). This type‐specific and group‐specific activity was confirmed by absorption experiments with both infected cells and concentrated intact and disrupted virus. Immunoprecipitation of highly purified, labelled proteins of the murine type‐C viruses with these antisera yielded a pattern of reactivity that correlated very well with those obtained by humoral cytotoxicity and, further, defined the polypeptide‐specific reactivities of these antisera. Cytotoxic activity obtained with p12 antisera was not well correlated with the intact virus content or the virus‐producing ability of different R‐MuLV shedding mouse cells whereas activity with gp70 antisera was. Cytotoxic activity was not observed with p10 or p30 antisera and virus‐specific cytotoxic activity was not observed with p15(E). Immunization of three strains of mice differing in their endogenous type‐C virus expression with inactivated, disrupted R‐MuLV yielded antisera active in radioimmuno‐assays to the homologous R‐MuLV proteins which were found to be immunologically active on the surface of the virus‐infected cell (gp70 and p12), as well as to the other type‐C viral proteins, p30, p15 and p10. The natural host's ability to respond immunologically to these viral proteins and the in vitro cytolysis of virus‐positive cells with antisera of this specific reactivity led to the conclusion that these viral proteins may play an important role as potential transplantation antigens in naturally occurring tumors.