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Evidence against expression of an endogenous murine leukemia virus causing cellular resistance to lysis by activated
L R Gooding1, J R Taylor, S M Laster
1Department of Microbiology and Immunology, Emory University School of Medicine, Atlanta, GA 30322.
Abstract:
In previous studies we observed that resistance of murine SV40-transformed fibroblast cell lines to cytolysis by activated macrophages was frequently associated with cellular expression of the gp70 of an endogenous ecotropic murine leukemia virus (MuLV). The work described here was initiated to test directly for a causative relationship between MuLV expression and resistance to lysis by macrophages. Northern blot analysis revealed that macrophage-resistant cells contain full length retroviral RNA. A panel of mAb which distinguish among host-range classes of MuLV detected only a non-recombinant ecotropic gp70 in these cells. The ecotropic MuLV from two independently derived macrophage resistant cells were isolated by limiting dilution cloning on Mus dunii fibroblasts. These viruses were then used to infect macrophage-sensitive cell lines and the resultant MuLV-positive cells tested for sensitivity to macrophage cytolysis. The MuLV-infected lines remained highly sensitive to macrophage lysis despite their high levels of cell surface gp70 and release of infectious MuLV. Thus, although we cannot rule out the possibility that MuLV or a product thereof is necessary for development of macrophage resistance in transformed cells, expression of MuLV per se is not sufficient to create the resistant phenotype.
Insights
Murine leukemia virus (MuLV) expression in transformed cells does not solely cause resistance to macrophage lysis. Further research is needed to determine if MuLV is necessary for this resistance.
Area of Science:
- Immunology
- Virology
- Cell Biology
Background:
- Previous studies linked macrophage resistance in murine fibroblast cell lines to gp70 expression of endogenous ecotropic murine leukemia virus (MuLV).
- The role of MuLV expression in conferring resistance to macrophage-mediated cytolysis was not fully understood.
Purpose of the Study:
- To directly investigate a causative relationship between MuLV expression and resistance to macrophage lysis.
- To determine if MuLV expression is sufficient to induce a macrophage-resistant phenotype in transformed cells.
Main Methods:
- Northern blot analysis to detect retroviral RNA in macrophage-resistant cells.
- Monoclonal antibody (mAb) analysis to identify the host-range class of MuLV gp70.
- Isolation and characterization of ecotropic MuLV from resistant cells.
- Infection of macrophage-sensitive cell lines with isolated MuLV and subsequent testing for sensitivity to macrophage cytolysis.
Main Results:
- Macrophage-resistant cells contained full-length retroviral RNA and expressed non-recombinant ecotropic gp70.
- Infection of macrophage-sensitive cell lines with ecotropic MuLV did not confer resistance to macrophage lysis.
- MuLV-infected cells maintained high levels of cell surface gp70 and released infectious MuLV but remained sensitive to lysis.
Conclusions:
- Expression of murine leukemia virus (MuLV) alone is not sufficient to induce resistance to macrophage-mediated cytolysis in transformed murine fibroblast cell lines.
- While MuLV expression may be necessary for the development of macrophage resistance, it does not appear to be the sole causative factor.