MAGNITUDE AND PATTERN OF THYMIC LYMPHOCYTE MIGRATION IN NEONATAL MICE

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Abstract
Neonatal mice were given a subcapsular, intrathymic injection of thymidine-3H using a modified microneedle technique, and the migration of labeled cells to spleen, lymph nodes, Peyer's patches, and bone marrow was followed radioautographically with time. Assuming that nonlabeled lymphocytes migrated in the same manner as labeled lymphocytes, it can be concluded that the majority of lymphocytes present within mesenteric lymph nodes (74%) and Peyer's patches (61%), and a large proportion of those located in popliteal lymph nodes (40%) and the spleen (26%), were of thymic origin. Evidence is presented indicating that these are minimum values. The difference in the magnitude of thymic cell migration to gut-associated lymphoid tissue on the one hand and to the spleen and popliteal lymph node on the other hand was tentatively attributed to antigenic stimulation from the intestinal flora which develops during the first days of life. Thymus-derived lymphocytes were scattered throughout the lymph node cortex and splenic follicles. No noticeable thymic cell migration to the bone marrow was found. Labeling indices in the peripheral lymphoid organs paralleled those of cortical thymic lymphocytes suggesting the thymic cortex as the major source of migrants.