Arthur Brown

Characterization of Fv-1 Gene-Product-Mediated Resistance Transfer

Fv-1 gene-specific resistance to ecotropic murine retroviruses can be transferred to permissive cells with RNA prepared from restrictive cells. The active RNA has a sedimentation coefficient of 20-22S at low ionic strength and multiple regions of activity (5-6S, 10-12S, 24-27S) at high ionic strength. The maximum level of resistance transfer cannot be enhanced with noninhibitory carrier RNA or facilitators of RNA uptake, and the maximum inhibition (40-60%) is independent of the MOI. The low efficiency of resistance transfer is, therefore, probably the result of a fraction of cells resistant to RNA uptake.

Characterization of Fv-1 host range strains of murine retroviruses by titration and p30 protein characteristics☆☆☆

Abstract A standardized, direct XC plaque assay was used to determine the titration hitness patterns of Fv-1 host range murine retroviruses obtained from various laboratories. The N- or B-tropic viruses were tested on a variety of cells with Fv-1 nn , Fv-1 bb , or Fv-1 nb genotypes, and, with one exception, a discrete two-hit pattern was obtained on cells with the restrictive genotype (i.e., N-tropic virus on BALB/c, SIM·R, and B6C3F 1 cells, and B-tropic virus on SME, SIM, and B6C3F 1 cells). The single exception to the two-hit titration effect was a strain (TOR-B) which is poorly infectious for all cells, and which does not show a clear N- or B-tropism. In addition, it was possible to convert the two-hit pattern of another B-tropic virus (OR-B) to a one-hit curve by coinfection with an XC-negative N-tropic virus. Relative to SC-1 (Fv-1 −− ) cells, it was possible to define three components of restriction of ecotropic virus infection of mouse cells: The first two components, the two-hit kinetics and 10 2- to 10 3 -fold reduction in titer on restrictive cells, are Fv-1 determined; the third a decreased infectivity on all cells relative to SC-1 cells, is independent of Fv-1 genotype.

Cross Protection among Togaviruses in Nude Mice and Littermates

After immunization with Sindbis virus, T-cell deficient nude mice, compared to normal littermates, were equally protected against challenge with Sindbis virus. However, the nude mice showed about one-tenth the protection observed with normal littermates after challenge with Semliki Forest virus at a dose of 100 LD50. This consistent with our previous interpretation that sensitized T-cell populations play a major role in cross protection between the two togaviruses. The remaining low level of specific cross protection in nude mice (detectable only at a challenge dose of 10 LD50) could not be attributed to an anamnestic response of neutralizing antibody to the challenge virus or to an effective antibody-dependent, complement-mediated cytolysis of infected cells in vivo. Other possible compensatory mechanisms to explain the low level of specific cross protection in nude mice are discussed.

Induction of Interferon in Hereditarily Asplenic Mice With and Without a Neonatal Spleen Cell Transplant

Summary Interferon production in hereditarily asplenic and normal mice following intravenous injection of Newcastle disease virus was compared. Serum from asplenic mice showed a significantly lower interferon level than normal littermates. A neonatal spleen cell transplant markedly enhanced interferon production in asplenic mice to the extent that they were able to produce amounts of interferon approximately the same as normal littermates with spleen.

Cross-reactive Target Antigen in Cell-mediated Cytolysis of Cells Infected with a Temperature-sensitive Mutant of Sindbis Virus

Cytotoxic T lymphocytes (CTL) against alphavirus-infected L929 cells were generated in mice by two in vivo immunizations of one virus or by in vivo immunization followed by in vitro stimulation of splenocytes with infected peritoneal exudate cells or splenocytes. These CTL caused specific H-2-restricted cytolysis equally well with homologous, heterologous or Sindbis virus ts20 mutant-infected cells. Thus, specific CTL appear to be cross-reactive components in normal immunity to alphaviruses and the E1 glycoprotein is implicated as the target antigen.

Lack of Interaction Between Sendai Virus and Bacterial Cells

Summary Fusion of E. coli cells and spheroplasts, B. megaterium cells and protoplasts, and M. laidlawii by UV-inactivated Sendai virus could not be demonstrated by direct methods or indirectly by recombination analysis. Studies show that E. coli cells and spheroplasts adsorb, in contrast to HeLa cells, only small amounts of Sendai virus, indicating that fusion may be blocked at the adsorption stage. The NANA in E. coli appears to be inaccessible to the virus neuraminidase.

Peritoneal Barrier to the Spread of Semliki Forest Virus in Mice

Abstract The LD50 for encephalitis caused by Semliki forest virus in 6– to 8-week-old mice is 1 plaque-forming unit (PFU) in C3H/Ten strain of mice when injected intracerebrally, iv, or in the footpad; however, the LD50 by the ip route is 4 × 103 PFU. In the ICR strain of mice at the same age, the LD50 for the intracerebral route is 1 PFU, 103 PFU for the iv and footpad routes, and 4 × 103 PFU for the ip route. A number of in vivo and in vitro experiments were done to explain the relative resistance to Semliki forest virus injection by the ip route. The results suggest that the viruses are adsorbed to and enter adherent cells of the peritoneal cavity but do not replicate and release progeny virus. After inoculation with the virus, viral antigens could only be observed in methanol-treated cells as a halo by immunofluorescence at or just below the plasma membrane of only a small fraction (<0.5%) of peritoneal adherent cells. Naturally occurring interferon-α/β (<1 unit/ml) was found to probably play a marginal role, if any, in the resistance.

Fv-1 Locus restriction of mouse retroviruses in glucocorticoid-treated cells

Abstract Treatment of mouse embryo cells with hydrocortisone (10 −6 M ) or dexamethasone (10 4 −10 −6 M ) increases virus synthesis whether the cells are permissive or restrictive at the Fv-1 locus. However, the number of cells infected was not increased in either permissive or restrictive cells by treatment with either glucocorticoid, and the two-hit titration pattern in restrictive cells remained unaltered. Therefore, the enhancement of virus replication by the glucocorticoids is independent of Fv-1 restriction and appears to occur after the Fv-I locus-sensitive step in virus synthesis.