Biological characterization and molecular cloning of murine C-type retroviruses derived from the TSZ complex from mainland China.

Characterization of the SRS murine retrovirus complex, derived from the TSZ system of murine leukemia developed in China, was carried out. The initial stock contained XC+, NB-tropic virus (and possibly other viruses), and induced several neoplastic diseases in neonatally inoculated NIH Swiss mice: erythroid leukemia, myeloid leukemia (acute myeloblastic leukemia), and lymphoblastic lymphoma (both B- and T-lymphoid). In addition, approximately 30% of inoculated animals developed central nervous system disease--hindlimb paralysis or semilateral paralysis. Rescue of virus from the spleen of an animal with combined erythroid/myeloid leukemia, followed by endpoint dilution gave two stocks: 19-6 (XC+, NB-tropic) and 19-7 (XC-, NB-tropic). Both stocks induced erythroid and myeloid leukemia, and 19-6 induced CNS symptoms as well. Southern blot analysis indicated that the predominant viruses from the 19-6 and the 19-7 cultures were related, but different in the env region. An infectious virus molecular clone of provirus from 19-6 cells was obtained. The resulting cloned virus [SRS 19-6 murine leukemia virus (MuLV)] induced four kinds of leukemia: erythroid, myeloid, B-lymphoma, and T-lymphoma; in many cases, more than one tumor type was identified in the same animal. Such a broad spectrum of leukemias induced by a cloned MuLV is unusual. Flaccid hindlimb paralysis induced by SRS 19-6 MuLV could be attributed to meningeal B-lymphoma. Immunofluorescent staining with a panel of env-specific monoclonal antibodies confirmed that the 19-6 and 19-7 viral stocks contained different viruses, which differed from previously characterized MuLVs. The viruses of the SRS complex may provide interesting reagents for investigations of MuLV-induced disease.