New cell surface gp70 related to Friend mink cell focus-inducing virus is expressed on Friend virus-induced erythroleukemic spleen cells after elimination of ecotropic Friend virus gp70 in Rfv-3r/s mice.

Abstract

Spleen cells from Rfv-3r/s mice with Friend virus-induced erythroleukemia were analyzed for expression of virus-induced proteins with monoclonal antiviral antibodies and conventional antisera. Leukemic spleen cells, 30-60 d after virus inoculation, expressed decreased amounts of ecotropic Friend murine leukemia helper virus gag- and env-encoded cell surface and intracellular proteins compared with leukemic cells tested 8-10 d after virus inoculation. In contrast, the spleen focus-forming virus-induced protein, gp55, was present on both leukemia cell populations. This difference appeared to be mediated by the humoral antibody response in Rfv-3r/s mice, which could recognize only ecotropic gag and env proteins, and not gp55. A new gp70 molecule cross-reactive with a recombinant Friend mink cell focus-inducing virus was found in large quantities on late leukemic cells. This protein appeared to be derived from a recombinant virus produced during the course of Friend virus infection. The appearance of this new gp70 suggests that recombinant viruses other than spleen focus-forming virus may play a role in Friend virus-induced erythroleukemia.

Identification of a unique erythroleukemia-associated retroviral gp70 expressed during early stages of normal erythroid differentiation.

“…In order to document that the 18-6 reactive determinant was expressed by a viral gp70 on the surface of these cells, we immunoprecipitated the radiolabeled cell surface proteins of early (10 d) FV spleen cells, late (30-60 d) FV spleen cells, the AA60 erythroleukemia cell line, and fetal liver cells and analyzed these proteins by SDS-PAGE. Early and late FV spleen cells from (B 10.A X A)F1 mice were previously found to differ in expression of both F-M uLV-encoded gp70 and a second gp70 unrelated to F-MuLV (13). As shown in Fig.…”

“…Previously, we suggested that the gp70 on FV erythroleukemia cells was serologically closely related to FMCF gp70 (13). However, antigenic analysis with monoclonal antibodies specific for MCF viruses including FMCF-1 (12,25) indicated that this gp70 did not express any MCFspecific antigens, nor did it react with any F-MuLV-specific antibodies (25) ( Table I).…”

“…This procedure has been published previously (13). Briefly, leukemic spleen cells, leukemia cell lines, and embryonic liver cells were washed three times with PBBS and resuspended in Dulbecco's phosphate-buffered saline (DPBS) at 20 × 10 ~ cells/ml.…”

“…Cowan I strain and analysis of immunoprecipitates by SDS-PAGE using autoradiography have been described previously (13). For reasons of low affinity, immunoprecipitation of F-MuLV gp70 required a mixture of antibodies 48 and 273, each of which reacts with a different epitope of the gp70 molecule (10).…”

“…Indirect membrane immunofluorescence on live cells was carried out in two ways. The standard technique utilizing monocional antibody and FITCconjugated goat anti-mouse Ig has been described previously (13). This assay was used on late Friend erythroleukemic spleen cells, leukemia cell lines, thymus, and fetal liver cells because of the relative paucity of membrane Ig-positive B lymphocytes.…”