Distribution of Short‐Lived and Long‐Lived Small Lymphocytes in the Lymphomyeloid Tissues of Germ‐Free NMRI Mice

Germ‐free and conventional NMRI nine were injected unit 3H‐thymidine daily for 30 days to label a high percentage of short‐lived (fast‐proliferating) small lymphocytes and cells with a long interphase–that is. long‐lived small lymphocytes Scintillation counting and autoradiographical procedures, including registration of labeling indexes and grain counts, were carried out on smears and sections of lymph nodes, spleen, thymus, bone marrow, thoracic duct lymph, and blood, and the number of blood and bone marrow lymphocytes was quantitated The distribution of labeled small lymphocytes in the various lymphoid smears and organs was similar in germ‐free and conventional mice, as were the numbers of blood and bone marrow lymphocytes The findings show that the percentage of short‐and long‐lived lymphocytes as well as the average turnover time of the latter cell category are identical in the two groups of mice studied This suggests that mechanisms other than antigen‐triggering are operating in the generation of shortlived and long‐lived small lymphocytes