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Evidence that a target-derived soluble factor is necessary for the selective lysis of SV40-transformed fibroblasts by
1Microbiology and Immunology, Emory University School of Medicine, Atlanta, GA 30322.
Abstract:
Our laboratory is investigating the basis for the selective recognition of transformed cells by activated mouse macrophages. As targets we are using a panel of SV40-transformed, C3H.OL fibroblast cell lines (SV-COL) that display widely different levels of sensitivity to lysis, from highly sensitive to completely resistant. Our results show that adding conditioned medium from the macrophage-sensitive target SV-COL-E8 (CM(E8] to a cytolysis assay with the macrophage-resistant target SV-COL-F5f causes the macrophages to kill the resistant targets in a contact dependent fashion. We have termed this activity "macrophage cell lysis factor" (MCLF). MCLF activity was not detected in conditioned media from cells not killed by activated macrophages (i.e., 3T3-like cell lines or embryo fibroblasts) but was present in conditioned media from six other SV-COL cell lines at levels that were directly proportional to the sensitivity of those targets (r = 0.98). These data suggest that MCLF plays a key role in determining the lytic sensitivity of SV40-transformed fibroblasts. Finally, to ask whether the production of MCLF is sufficient to explain the selective recognition of SV40-transformed fibroblasts by activated macrophages we have tested whether CM(E8) will cause macrophages to kill normal cells. Our results show that in the presence of CM(E8) macrophages will kill immortalized, 3T3-like fibroblasts but will not kill normal embryo fibroblasts. These results suggest that the production of MCLF, or a similar activity, is necessary but not sufficient for macrophage cytolysis to occur and that a change in target cell phenotype that occurs during the process of immortalization is also required.
Insights
Researchers identified a macrophage cell lysis factor (MCLF) crucial for selective killing of transformed cells. MCLF production is necessary but not sufficient, requiring target cell immortalization for macrophage-mediated lysis.
Area of Science:
- Immunology
- Cell Biology
- Cancer Research
Background:
- Activated macrophages selectively recognize and eliminate transformed cells.
- The precise mechanisms underlying this selective recognition remain incompletely understood.
Purpose of the Study:
- To investigate the molecular basis for selective macrophage-mediated lysis of SV40-transformed fibroblasts.
- To identify factors involved in target cell recognition and susceptibility to lysis.
Main Methods:
- Utilized a panel of SV40-transformed fibroblast cell lines (SV-COL) with varying lysis sensitivities.
- Assayed conditioned media for "macrophage cell lysis factor" (MCLF) activity in contact-dependent cytolysis assays.
- Tested the effect of MCLF on normal and immortalized fibroblasts.
Main Results:
- Conditioned medium from sensitive SV-COL cells (CM(E8)) induced lysis of resistant SV-COL targets by macrophages.
- MCLF activity correlated directly with target cell sensitivity to lysis (r = 0.98).
- CM(E8) enabled macrophage lysis of immortalized fibroblasts but not normal embryo fibroblasts.
Conclusions:
- MCLF plays a key role in determining the lytic sensitivity of SV40-transformed fibroblasts.
- MCLF production is necessary but not sufficient for macrophage-mediated cytolysis.
- A change in target cell phenotype during immortalization is also required for selective macrophage recognition and lysis.