Characterization of env gene recombination in X‐ray‐induced thymomas of C57BL76 mice

A role for specific recombination events at the env region of endogenous murine leukemia virus (MuLV) sequences in radiation carcinogenesis in C57BL mice has been suggested by a number of studies. We characterized env‐related cell surface antigens from a primary, x‐ray‐induced, and several transplanted C57BL/6 thymomas of viral and radiation etiologies by immunoprecipitation and two‐dimensional peptide mapping. DNA from lymphoma cells was also analyzed by Southern blotting for evidence of mink cell focus‐forming (MCF) type env recombination events. Although gp70 molecules with novel structural determinants were found on all transplanted lymphomas examined, expression of novel env antigens was variable among these lymphomas, and there was a lack of correlation of characteristic MCF‐type env recombination events in endogenous retrovirus DNA sequences with novel env antigens on lymphoma cell surfaces. Neither novel gp70 antigens nor MCF‐type env provirus recombinant structures were consistent features of the C57BL/6 thymomas of radiation etiology examined in this study, even though MCF‐type env recombination events have been suggested as etiologically significant in MuLV‐mediated lymphomagenesis in both RadLV and x‐ray‐induced tumors in C57BL/6 mice.