Presence of a novel recombinant murine leukemia virus-like glycoprotein on the surface of virus-negative C57BL lymphoma cells.

A line (BL/RLi2-NP) of C57BL mouse cells derived from an X-ray-induced thymic lymphoma was free of murine leukemia virus (MuLV) and expressed no viral antigens as determined by potent antisera reactive with group-specific determinants of MuLV p30 and gp70 polypeptides. However, using an antiserum directed against the gp70 of the VL-3 isolate of radiation leukemia virus, which reacted predominantly class specifically with recombinant (RM) MuLVs in neutralization, a proportion of BL/RL,2-NP cells or their clones were clearly positive. In contrast, BL/RL,?-NP cells could be killed in complementdependent cytotoxicity, however, by both group and RM MuLV class-specific anti-gp70 sera. Both sera also precipitated a gp70 from the surface of BL/RL12-NP cells. This gp70 was also found free in BL/RLi2-NP cell culture fluids. The BL/RL12NP gp70 was isolated from cell culture fluids by immunoaffinity chromatography, and oligopeptide maps were prepared follow ing trypsin and chymotrypsin digestion. It appeared to be a single species resembling those found in RM MuLV gp70s but had a unique pattern of peptides. Individual peptides could be identified as having probably been derived from either ecotropic or xenotropic classes of MuLVs. The BL/RL12-NP cells could be superinfected with ecotropic MuLVs but not with xenotropic MuLV. Infection with RM MuLV was very difficult but could be achieved with time. An exami nation of the RM MuLV progeny indicated that some virus had additional envelope components compatible with endogenous ecotropic MuLV gp70. The BL/RL,2-NP gp70 was compared to another RM-type gp70 found on the cell surface of a virus-free Swiss mouse lymphoma line. The role of such non-virion-associated cell surface RM gp70s in leukemia is discussed in the context of signal hypotheses of autostimulatory blastogenesis.