The role of the Peyer's patch in the carcinogenesis of lymphoid cells

The dose response to 3-methylcholanthrene (3-MC), the promoter effects of 2,6,10,14-tetramethylpentadecane (pristane) and the target-organ specificity in the preferential induction of B-lymphoid malignancies versus thymic tumors were examined. Lymphoid malignancies were induced in approximately 30% of the Copenhagen rats treated with injections in Peyer's patches (PP) of low, intermediate or high doses of 3-MC. A low dose of 3-MC induced B-lymphocytic leukemias or B lymphomas, whereas thymic tumors were detected in rats treated with high doses. Co-treatment of rats with pristane and 3-MC resulted in increased incidences and decreased latency of the lymphoid malignancies observed, suggesting that pristane acts as a tumor promoter. To address the possible role of PP in the induction events, PP were surgically removed after 3-MC treatment and the remaining small intestine anastomosed. Thymic tumors, but no B-lymphoid malignancies, were observed, indicating that the PP environment was important in the induction of the B-lymphoid malignancies. Radiotracer studies also revealed that appreciable amounts of 3-MC were disseminated to the thymus within 24 hr after treatment of PP with a high dose of 3-MC. Furthermore, direct intrathymic injection of the thymus with 3-MC resulted in the development of thymic tumors only. These results support the hypothesis that the PP has an important role in early events in the carcinogenesis of B lymphocytes and in the dissemination of 3-MC to the thymus.