Immunodepressive Effect of 3-Methylcholanthrene. Antibody Formation at the Cellular Level and Reaction Against Weak Antigenic Homografts2

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Abstract
3-Methyldiolanthrene (MCA) administered to mice reduced the number of antibody-producing spleen cells after immunization with sheep erythrocytes measured at a single cellular level. The immuno-depression was rapid and long. Even 2 days after MCA exposure, when test antigen was given, the number of plaque-forming spleen cells (PFC) decreased more than 50 percent. After a single exposure to MCA, the PFC remained depressed for a period corresponding to the latency period prior to the appearance of the MCA-induced sarcomas. This depression of PFC was studied in groups of mice at different intervals between 1 and 20 weeks after MCA administration. Spleen weight and total spleen cell number were reduced, and there was a specific reduction of PFC when expressed as a fraction of the total number of spleen cells. The depression of the cellular immune response was compared with the humoral hemolysing and hemagglutinating antibody response toward a heterologous test antigen, sheep erythrocytes. Impairment of the graft rejection after MCA exposure, tested across a monospecific weak histocompatibility barrier (H-1) by skin grafting, was first demonstrable at the time of tumor appearance. Skingraft survival was not affected during the earlier part of the tumor latency period. The findings are discussed in relation to an earlier suggestion of Prehn and Main that MCA inhibits immunological responses and thereby allows the outgrowth of antigenic neoplastic cells.