Systemic effects of methylcholanthrene in mice. II. Immune responses to sheep red cells.

Assays of splenic plaque-forming cells (PFC) for sheep red cells (SRC), done in parallel in control and methylcholanthrene (MCA)-injected mice of strains C3H/eB and C57BL/6, disclosed immunodepression, the degree of which depended on strain and sex of mice, and time elapsed between injection of MCA and performance of test. The most severe and long-lasting effects were observed in male C3H/eB mice, and the least impairment was seen in female C57BL/6 mice. After surgical splenectomy for assay of PFC, MCA-injected mice were observed for appearance of induced tumors up to 52 weeks after administration of carcinogen. In most groups of C57BL/6, but only rarely in C3H/eB mice, a correlation was found in individual mice between immunodepression and appearance of tumor. Since, however, the incidence of induced tumors was higher in C57BL/6 than in C3H/eB mice, immunodepression cannot be considered a universally obligatory step in carcinogenesis, but its involvement may be limited to particular phenotypes.