Alfred Hellman

Depression of Mitogen-Induced Lymphocyte Blastogenesis by Baboon Endogenous Retrovirus-Associated Components

Abstract Freeze/thaw (F/T) extracts of gradient purified concentrates of baboon endogenous retrovirus (BEV) depress phytohemagglutinin (PHA)-induced blastogenic transformation of human, baboon, and mouse lymphocytes. Extracts of normal fetal dog thymus cells (vehicle for virus replication), pelleted virus cores, spent tissue culture medium, and virus suspension buffers were not depressive. Sephacryl S-200 chromatography of BEV F/T extracts yielded two peaks of suppressive activity; peak A, eluted in the region of relatively high protein concentration with the 45,000-dalton ovalbumin marker, was highly labile, but not cytotoxic. Peak B, eluted between cytochrome c and DNP alanine markers, contained no detectable protein and appeared to consist of two components; one cytotoxic and highly labile and a second, noncytotoxic and relatively stable. A polyvalent antiserum to BEV proteins precipitated components of the BEV F/T extract and peaks A and B, but failed to abrogate immunodepression.

Studies of the blastogenic response of murine lymphocyte. Iii. Specific viral transformation.

Summary Data presented suggests that either specific lymphocytes or specific sites on such cells are committed to both specific and nonspecific lymphocyte transformation responses. Though the animal may be immunologically depressed by leukemia virus infection (RLV), its lymphocytes are still capable of a limited but significant cellular immune response to specific viral and PHA stimulation.

Direct isolation of xenotropic retraviruses from the NIH swiss mouse uterus.

Abstract Xenotropic type C retraviruses were isolated from cell-free uterine extracts of normal adult NIH Swiss mice by direct inoculation of mink, cat, and human target cells. Successful isolation occurred in approximately one-half the susceptible target cell cultures inoculated with a given extract. These results demonstrate the presence of fully infectious xenotropic virus particles in the uterus of the normal NIH Swiss mouse.

Group specific antigen and RNA-directed DNA polymerase activity in normal baboon placenta.

Summary C-Type particles were observed in normal baboon placentas at various stages of gestation. This tissue was found to have interspecies specific antigens of the C-type RNA tumor viruses and RNA-directed DNA polymerase activity that could not be inhibited by antisera prepared against the previously recognized reverse transcriptases of several RNA tumor viruses. This study was funded in part by Contract NIH-NCI-E-71-2348 from the Special Virus Cancer Program, NCI; Grant RR00361 from the U.S. Public Health Service and WHO Grant Z2/181/27. The laboratory at the Southwest Foundation for Research and Education serves as the WHO Regional Reference Center for Simian Viruses.

Cell Surface Binding Proteins for the Major Envelope Glycoprotein of Murine Leukemia Virus

Summary The 71,000 Mr major envelope glycoprotein (gp71) of Rauscher murine leukemia virus has been shown to bind to susceptible cells in vitro. [3H]Leucine surface polypeptides bound to 125I-labeled gp71 were stripped from BALB/c thymocytes with nonionic detergent and chemically linked with the cleavable bifunctional reagent methyl 4-mercaptobutyrimidate. Soluble disulfide-linked 125I-labeled gp71 bound thymocyte surface polypeptide oligomers were precipitated with adsorbed gp71 antisera and after reductive cleavage, molecular weights (SDS-PAGE) of approximately 23,000, 32,000, 45,000, 65,000, 90,000, and 170,000 M r were seen. Experiments demonstrating the cross-linked-dependent immunoprecipitation of 125I-labeled gp71 - thymocyte surface polypeptide oligomers with antiserum having reactivity to products of the major histocompatibility locus (H-2d and la) and also for the gag gene products (p30 and p15) are described. The involvement of these thymocyte surface polypeptides in structuring the functional receptor for ecotropic oncornaviruses is discussed.

Oncornaviral Protein Modulation in Mouse Uterine Tissue by Estrogen

Summary Treatment of ovariectomized NIH Swiss mice with estrogens elevated the level of the murine leukemia virus group specific protein and the activity of an RNA-di-rected DNA polymerase in the uterus. The extent that these markers were raised was dependent on the relative biological potency of the estrogen and on the time interval following treatment. Increases in the levels of both viral marker proteins were evident within 24 hr of treatment and were highest at 48 hr. Subsequently, viral protein levels declined to pretreatment levels. The authors acknowledge the technical assistance of Carl Reed, Carol Lipson, Leon Culler, Sara Myers, and Philip Errico. Antisera used in this study were prepared by Dr. R. Wilsnack, Huntington Research Center, Baltimore, MD.

Susceptibility of Baboon (Papio doguera) Kidney Cells to Human Enteroviruses.

Summary Baboon (Papio doguera) kidney cells demonstrate a susceptibility to human enteroviruses, in general, similar to that of the rhesus monkey. Its relative freedom from “native” viruses and ability to demonstrate the presence of SV40 virus suggests a more widespread application to virological studies and vaccine production.

Enhancement of Encephalomyocarditis Virus Replication in L Cells Treated with Insulin

Abstract Data are presented which show that treatment of L cells with low levels of insulin results in a marked increase in the yield of encephalomyocarditis virus, strain MM. Maximum yields were obtained when the cell cultures were pretreated with the hormone for 24 hr followed by the presence of insulin after virus infection. The increased virus yields cannot be attributed either to increased cell proliferation or to interference with the interferon system.

Studies on the blastogenic response of murine lymphocytes. I. Quantitative measurement of stimulation by phytohemagglutinin.

Summary A sensitive and reliable system to culture mouse lymphocytes stimulated to transform by phytohemagglutinin is described. This system permits the convenient use of a relatively rapid modified “acidinsoluble” method to assay nucleoside incorporation. Under the conditions described, stimulated splenic and peripheral lymphocytes demonstrated elevated RNA synthesis 18-24 hr prior to maximum DNA synthesis. Nucleoside incorporation of stimulated peripheral lymphocytes exceeded that of splenic cells and occurred earlier. The degree of transformation was dependent on cell density, phytohemagglutinin-P concentration, and serum level.

Protease Inhibitors Modify Induction of Endogenous Type C Oncornavirus

Abstract The influence of the protease inhibitors, antipain and leupeptin, on type C virus induction from mouse cells by 5-iodo-2-deoxyuridine (IdUrd) and ultraviolet (uv)-irradiated herpes simplex virus (uv-HSV) was studied. Exposure of unaltered intact A1-2 cells, derived from the BALB/c mouse, to these inhibitors decreased the level of endogenous type C virus normally induced by IdUrd or uv-HSV treatment. Dose-response studies showed that antipain was more suppressive of virus induction than leupeptin. Virus induction was suppressed at inhibitor concentrations which did not appreciably affect cellular macromolecular synthesis or capacity of noninduced cells to support helper virus replication upon exogenous infection. These results suggest that the inhibitors affect the virus induction process. Our results are similar to those reported for antipain inhibition of λ-prophage induction in Es-cherichia coli, and corroborate a recent report on suppression of mammalian virus induction by these protease inhibitors.