The role of the spleen in tumor bearing host: I. Characterization of spleen cells in tumor-bearing mice.

Morphologic changes of the spleen and dynamic changes of biologic activity of spleen cells from C3H/HeJ mice bearing methylcholanthrene induced fibrosarcoma (MCA-F) were investigated in different stages of tumor growth, using local adoptive transfer assay (LATA). The spleen size, weight and the number of spleen cells increased with the tumor growth. In early and late stages of tumor growth, tumor-bearing mice possessed non-specific tumor-enhancing cells which were radioresistant (700 rads), phagocytic and adherent, suggesting that they were macrophages. On the other hand, in middle stages of tumorgenesis, tumor-bearing mice possessed specific cytotoxic cells which were radiosensitive (700 rads) and anti-Thy 1.2 serum positive, suggesting that they were T-cells. Thus, the appearance of tumor-enhancing cells was earlier than cytotoxic cells in MCA-F bearing host, and the balance of tumor-enhancing and cytotoxic cells may influence the tumor outgrowth in different stages of tumorgenesis. The spleen serves as a reservoir of factors which either abrogate cell mediated resistance or stimulate neoplastic growth, or as the source of cytotoxic cells, at certain times of tumor burden.