Comparison of lymphocyte production in lymphoid organs and their compartments using the metaphase-arrest technique.

Lymphocyte proliferation was studied in normal young anesthetized pigs by the metaphase-arrest technique using vincristine (VCR). In each animal biopsies were taken simultaneously from the thymus, mesenteric lymph nodes, spleen, palatine tonsil and Peyer's patches from the ileum and jejunum. After taking the first samples, 0.25 mg VCR/kg body weight was injected i.v. and then four more biopsies were excised for up to 3.5 h after VCR. Imprints of the lymphoid organs were evaluated as an overall index for each organ, and histological sections were used to determine the mitotic index in typical B- and T-lymphocyte areas in these organs. In follicles of mesenteric lymph nodes, tonsils and the two types of Peyer's patches a comparable increase in the mitotic index was found, 3.62% per hour. In the corona the increase was also comparable but much lower, 0.43% per hour and in the interfollicular area similarly 0.38% per hour. In the spleen the mitotic rate was 0.69% for the white pulp and 0.42% per hour for the red pulp. In the thymic cortex the mitotic index increased by 0.49% and in the medulla by a surprisingly high value of 0.32% per hour. The metaphase-arrest technique in larger animals enables a comparison of lymphocyte production among organs and their different compartments, and demonstrates the important contribution of peripheral lymphoid organs to the renewal of the lymphocyte pools.