Isolation of a unique retrovirus, MNV-1, from Macaca nemestrina

Cell cultures established from the spleen of a Macaca nemestrina with enzootic retroperitoneal fibromatosis (ERF) spontaneously released a unique retrovirus. Throughout 14 serial passages, the spleen cell cultures remained fibroblastic and no cytopathic effect was evident. The virus incorporates [ 3H]uridine, contains an RNA-dependent DNA polymerase (RDDP), has a buoyant density of 1.15 g/cm 3 in sucrose, and was designated MNV-1. Virion-associated reverse transcriptase showed no preference for either Mg 2+ or Mn 2+ in standard RDDP assays. Complementary DNA (cDNA) transcribed from polyadenylated MNV-1 RNA hybridized to genomic DNA and RNA extracted from diseased tissues but not to nucleic acids from normal tissues of a healthy Macaca nemestrina or a Macaca mulatta. MNV-1 is therefore exogenous to these species. MNV-1 had no detectable homology to the endogenous macaque virus isolates MAC-1 and MMC-1. Liquid hybridization of MNV-1 cDNA to viral RNA derived from exogenous and endogenous subhuman primate retroviruses (SiSV(SSAV), GALV-SF, BaEV-M7, and BILN) did not reveal any significant sequence homologies. In addition, MNV-1 does not share homology with bovine leukemia virus or Mason-Pfizer monkey virus as determined by Southern blot hybridization. We conclude that MNV-1 is a unique retrovirus which has not previously been described. As the ultrastructure of virions in in vitro cell cultures, as well as disease involved tissue, show some particles with type C morphology and others with type D morphology, MNV-1 may be comprised of more than one component.