Production of antitumor cytostatic factors by nonactivated resident macrophages of the peritoneal cavity of Syrian hamsters

The production of soluble cytostatic (CS) factor(s) by nonactivated peritoneal resident macrophages (Mph) of Syrian hamsters was found with the use of susceptible spontaneously transformed in vitro cells of STHE cell strain. The CS factor was determined by two modifications of CS test: 1) incorporation of 3H-TdR to the nuclei of target cells and 2) direct determination of the number of cells in the wells. The selected in vivo highly malignant variant of STHE strain appeared to be resistant to CS factors Mph.