Outer membrane of avian myeloblastosis virus

Cell culture density modulates the incorporation of HLA antigens by enveloped viruses

Uninfected, as well as feline leukemia virus (FeLV) infected human cells cultured under high cell density conditions undergo changes in the expression of major histocompatibility complex (MHC) antigens, as determined by indirect trace binding radio immunoassay (RIA) using monoclonal anti-HLA antibodies and by decreased sensitivity to complement mediated cytotoxicity by anti-HLA alloantibodies. FeLV particles produced by the viral infected cells are also sensitive to neutralization by anti-HLA antibodies, suggesting that enveloped viral particles incorporated MHC antigens in the viral envelope. The amount of HLA antigens expressed in the viral enveloped, closely reflects the expression of HLA antigens by the virus-producer lymphoid cells. FeLV-infected HsB-2 (T) and SB (B) lymphoid cells cultured under high cell concentration condition show decreased expression of some HLA antigens (A2, B12, B17), and the viral particles produced by those cells also incorporate lower amounts of such antigens. Our results, based on the findings that human lymphoid cells (uninfected, as well as FeLV infected) show decreased expression of some HLA membrane determinants when grown under high cell density conditions, indicate that no viral selective mechanism operates in the incorporation of HLA determinants by enveloped viruses. Instead, our results suggest that viruses pick up MHC antigens from the host cell membrane according to the concentration of those antigens on the surface of the cells at the time of virus budding.

Proteins of bovine leukemia virus. I. Characterization and reactions with natural antibodies

The bovine leukemia virus (BLV) was purified from a chronically infected fetal lamb kidney cell line. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis of this virus revealed the presence of eight distinguishable viral components with molecular weights ranging from 80,000 to 11,000. The major component is a non-glycosylated protein having a molecular weight of 24,000 (p24). At least three heavier polypeptides were found, one of them representing a glycoprotein (gp 60). In addition, four minor polypeptides with respective molecular weights of 19,000, 16,000, 13,000, and 11,000 were identified. In a complement fixation assay using naturally occurring antibodies of a leukemic cow, four polypeptides, which included gp 60, p35, p24, and p16, were found to be reactive.