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Mitogenic activity elaborated by macrophage-like cell lines acts as competence factor(s) for BALB/c 3T3 cells
Abstract:
The culture medium from several murine macrophage-like cell lines contained a mitogenic activity that functioned synergistically with platelet-poor plasma to induce DNA synthesis in quiescent density-inhibited BALB/c 3T3 fibroblasts. This mitogenic activity was generated by P388D1 (and other established lines of) macrophage-like cells that were cultured either in medium alone or in medium supplemented with platelet-poor plasma. The amount of mitogenic activity produced was directly related to the length of time the macrophage-like cells were maintained in the medium. Serum-free medium conditioned by macrophage-cells did not stimulate DNA synthesis in density-inhibited 3T3 cells in the absence of plasma; however, a transient (4-hr) exposure to serum-free macrophage-conditioned medium allowed quiescent cells to respond to plasma-derived progression factors. The addition of plasma to 3T3 cells that had been treated with the macrophage-conditioned medium brought about DNA synthesis after a 12-hr lag. The mitogenic activity that was in macrophage-conditioned medium bound to DEAE-Sephadex and eluted in a single peak using a linear NaCl gradient. This macrophage-derived competence factor was not mitogenic for lymphocytes and was clearly separated by DEAE-Sephadex chromatography from the major peak of the previously described mitogenic monokine, Interleukin-1 (lymphocyte activating factor).
Insights
Murine macrophage cells release a factor that, with plasma, stimulates fibroblast DNA synthesis. This novel competence factor, distinct from Interleukin-1, primes cells for plasma-derived growth signals.
Area of Science:
- Cell Biology
- Immunology
- Biochemistry
Background:
- Murine macrophage cell lines produce factors influencing fibroblast proliferation.
- Macrophage-derived factors can synergize with plasma components to induce DNA synthesis.
- Understanding these interactions is key to deciphering cell growth regulation.
Purpose of the Study:
- To investigate the mitogenic activity in conditioned medium from murine macrophage cell lines.
- To characterize the nature of the factor responsible for inducing DNA synthesis in fibroblasts.
- To differentiate this factor from known mitogenic monokines like Interleukin-1.
Main Methods:
- Culturing murine macrophage-like cell lines (e.g., P388D1) in various media.
- Assessing DNA synthesis induction in quiescent BALB/c 3T3 fibroblasts.
- Utilizing serum-free conditioned media and platelet-poor plasma.
- Employing DEAE-Sephadex chromatography for factor purification and separation.
Main Results:
- Macrophage-conditioned medium contained a mitogenic activity that synergized with platelet-poor plasma.
- This activity induced DNA synthesis in density-inhibited 3T3 fibroblasts.
- The factor required transient exposure to conditioned medium for cells to respond to plasma.
- DEAE-Sephadex chromatography separated the mitogenic activity from Interleukin-1.
Conclusions:
- Murine macrophages secrete a competence factor that primes fibroblasts for plasma-induced mitogenesis.
- This factor is distinct from Interleukin-1 and plays a role in cell cycle regulation.
- The findings highlight a novel pathway for macrophage-fibroblast communication in growth stimulation.