Chemotactic activity for mononuclear phagocytes of culture supernatants from murine and human tumor cells: Evidence for a role in the regulation of the macrophage content of neoplastic tissues

Culture supernatants from 14 mouse solid tumors, 2 mouse lymphomas, 8 human solid tumor lines and 3 human leukemia-lymphomas were examined for chemotactic activity in blind-well chemotaxis chambers using murine peritoneal macrophages and human blood monocytes as indicator cells. Culture supernatants from various murine and human solid tumors had appreciable chemotactic activity for mononuclear phagocytes. Chemotactic activity was found in murine tumors of different histology and transplantation history, including autochthonous mammary carcinomas and chemically-induced sarcomas. Chemotactic activity was not unique to neoplastic cells because it was detected also in supernatants of two preparations of mouse embryo fibroblasts and two human lung embryo fibroblast lines. Production of tumor-derived chemo-attractants did not require serum in the culture medium, was inhibited by the protein synthesis inhibitor Cycloheximide, but was unaffected by the DNA synthesis inhibitor Mitomycin C. Murine supernatants were active on human monocytes and vice-versa. A first preliminary characterization of the chemotactic activity of the human sarcoma line 8387 revealed that it was not dialyzable, that most of the activity was retained at 56°C for 30 min, but not at 100°C, and that it was susceptible to proteolytic enzymes (trypsin and proteinase K) but unaffected by DNase and RNase. Upon fractionation on a Sephadex G-75 column, the activity eluted in a single, relatively broad peak in the cytocrome C region, corresponding to an apparent molecular weight of about 12,000. In the significant, though far from absolute, correlation (r = 0.71, p = 0.013) was found between chemotactic activity in culture supernatants (expressed as area under the chemotaxis titration curve) and the percentage of tumor-associated macrophages. It is suggested that tumor-derived chemotactic factor(s) play a role in the regulation of the macrophage content of neoplastic tissues.