Group-specific antigen of avian leukosis viruses. Virus specificity and relation to an antigen contained in Rous mammalian tumor cells

Expression of avian reticuloendotheliosis virus envelope confers host resistance

We constructed two reticuloendotheliosis virus (REV) envelope gene expression plasmids, one containing the REV-A envelope gene, the other the spleen necrosis virus (SNV) envelope gene. Cell lines were generated by transfecting each of the REV envelope plasmids into D17 cells, a canine cell line. The levels of REV envelope glycoprotein in the cell lines were assayed by immunoprecipitating the envelope glycoproteins from lysates of cells that were labeled with [35S]methionine. Virological challenge assays determined the degree of resistance of each of the cell lines to REV-A or SNV infection. The expression of either envelope gene protected the cells from infection by either REV-A or SNV virus. Several cell lines were significantly more resistant to REV infection than the parental D17 cells, and two lines were 25,000-fold more resistant, approaching the resistance of REV-infected D17 cells to reinfection. The resistant cell lines were not able to confer resistance to susceptible cells by cocultivation. The level of resistance was correlated with the uniformity of expression of the REV envelope glycoproteins by the individual cells in a cell line and not with the absolute level of expression by the population of cells.

Incomplete viral genome in a non-virogenic mouse tumour cell line (RVP3) transformed by Prague strain of avian sarcoma virus

Two cell lines, RVP3 and RVA4, derived originally from mouse tumors induced by the Prague and Schmidt-Ruppin strain of RSV, respectively, were studied. tall attempts failed to induce infectious virus production in RVP3 cells by fusion with chicken fibroblasts even if the cells were infected with avian leukosis viruses. Also, attempts to rescue the viral genome by transfection were unsuccessful. RVP3 cells harboured 31-45% of the viral genome sequences, as was shown by molecular hybridization, and therefore they were designated cryptovirogenic. The tumour cell line RVA4 did not contain any detectable viral sequences. The significance of the detection of the incomplete Rous virus genome sequences in mammalian cells is discussed.

Immunological and biophysical separation of dengue-2 antigens

Antigenic compositions of slowly sedimenting dengue-2 hemagglutinin (SHA) and soluble complement-fixing antigen (SCF) were compared with the virion (rapidly sedimenting hemagglutinin, RHA) by radioimmune precipitation (RIP), RIP inhibition, kinetic neutralization, and neutralization blocking tests with the use of hyperimmune mouse ascitic fluids. RHA and SHA were unable to inhibit completely the RIP of each other by anti-RHA, and neutralization by anti-RHA was not blocked by SHA. This indicated that SHA is serologically related, but not identical, to RHA. SHA differed from RHA in that SHA lacked the "core" polypeptide but contained the two envelope polypeptides. In addition, SHA contained a polypeptide with a molecular weight of 16,500 daltons and a suggestion of several other proteins. These data, when considered with other evidence, suggest that SHA is a special form of "incomplete virus." SCF was unable to inhibit the RIP of SHA or RHA or to block neutralizing antibodies. Further, anti-SCF did not neutralize RHA or precipitate significant levels of SHA or RHA. Polyacrylamide gel electrophoresis separated SCF from structural polypeptides by molecular size. This evidence suggests that SCF is a nonstructural antigen.

Virus-specific antigens in hamster cells transformed by Rous sarcoma virus

Virus-specific antigens were studied in hamster cells transformed by Rous sarcoma virus (RSV). Antigens were localized in the cytoplasm, as demonstrated by fluorescent antibody staining of fixed cells as well as by complement fixation (CF) following subcellular fractionation. Cytoplasmic extracts were analyzed by velocity and isopycnic centrifugation. CF antigens were found in a soluble form and in association with membranes and polyribosomes. Isolated plasma membranes had no CF antigen. Both soluble and particulate fractions with CF activity contained the same antigenic determinants by Ouchterlony analysis. These antigenic determinants were identical to those released by ether treatment of RSV.

Multiple group-specific antigen components of avian tumor viruses detected with chicken and hamster sera

Multiple group-specific (gs) components of the avian leukosis-sarcoma viruses were detected by immunodiffusion (Ouchterlony) tests with sera from hamsters bearing tumors induced by sarcoma viruses and with sera from adult chickens immunized with avian sarcoma or leukosis viruses. Immune hamster sera detected up to four components, whereas chicken sera detected at least one. The hamster and chicken sera identified a similar antigen, as indicated by reactions of identity. Relatively few chicken sera containing neutralizing antibody to avian sarcoma or leukosis viruses reacted in immunodiffusion with the gs antigen. The gs components were released from the virion by various means of disruption, including freezing and thawing. Tests with tissues from normal chickens and from chickens with Marek's disease failed to demonstrate any reactions with hamster or chicken gs antiserum.