Characterization of Anti-Inflammatory Factors Produced by Murine Tumor Cells in Culture23

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Abstract
P-815 mastocytoma cells from DBA/2 mice and a 3-methylcholanthrene-induced fibrosarcoma from C57BL/6 mice produced in culture at least two soluble anti-inflammatory factors that inhibited macrophage accumulation in vivo when the factors were injected sc into syngeneic recipients. One factor was a low-molecularweight peptide <1,000), as judged by ultrafiltration, failure of extraction by lipid solvents, nonsusceptibility to DNase or RNase, partial inactivation by trypsin, and complete inactivation by carboxypeptidase B. The second anti-inflammatory factor had a molecular weight between 30,000 and 100,000 and was also not extractable with lipid solvents. Production of anti-inflammatory factors by P-815 mastocytoma cells was inhibited by cycloheximide and cell irradiation but not by colchicine pretreatment of the cells, suggesting a relationship to protein synthesis rather than cell growth. Soluble anti-inflammatory factors depressed granulocyte as well as macrophage responses. Anti-inflammatory factors were not found in supernatants from cultures of splenocytes, peritoneal exudate cells, or murine lung fibroblasts.