Age-Dependent Tumor-Host Barrier and Effect of Carcinogen-Induced Immunodepression on Rejection of Isografted Methylcholanthrene-Induced Sarcoma Cells2

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Abstract
The immune status of CBA male mice, after immunization against sheep red blood cells, varied with age. The number of plaque-forming spleen cells (PFC) was measured with the Jerne test in mice of different ages. A parallel variation was found in the takes of first-generation transplants of sarcomas induced by 3-methylcholanthrene (MCA) tested in CBA male mice of the following ages: 1 week, 1 month, 3, 4½, 6, 10, 15, and 22 months. Maximum number of PFC and maximum resistance to tumor cells, transplanted at a dose of 103, were found in the 6-month-old age group. Takes were 100% in 1-week-old and 22-month-old mice, both groups having a minimum of PFC. MCA administration depressed the number of PFC and the resistance to antigenic MCA-induced isografts. The immunodepressive effect on PFC was independent of age, if expressed on a percentage basis. When the takes of 75 first-generation, MCA-induced sarcomas were tested after 103−106 cells were grafted to hosts both exposed and unexposed to MCA, a significantly higher number of takes and earlier tumors were seen in the MCA-exposed hosts. The change in immunological reactivity with age, as well as the immunodepressive effect of the carcinogen, may be relevant to the possible breakdown of the immunological surveillance mechanisms capable of preventing the outgrowth of antigenic neoplastic cells.