Kinetics of Theta‐Positive and Theta‐Negative Lymphocytes in Thymus‐Deprived and Normal Mice

Life spans and proliferative kinetics of theta‐positive (θ+) and theta‐negative (θ‐) cells were evaluated in normal, neonatally thymectomized (NeoTx) and sham‐thymectomized (ShamTx) Balb/c mice. This was done by exposing cell suspensions, incubated with anti‐θ antiserum + complement, to a dye exclusion test followed by fixation and autoradiography. Results from normal mice given [ 3 H]thymidine injections 5 weeks before being killed indicated that long‐lived θ+ and θ‐ cells constituted about equal percentages of the respective populations in peripheral lymphoid tissues. Long‐lived θ+ cells constituted a relatively high percentage of θ+ cells in the bone marrow, whereas a minority of the Θ‐ lymphocytes were long‐lived. Results from NeoTx and ShamTx mice, given intensive injections of [ 3 H]thymidine, showed that the θ‐ cells of the mesenteric nodes were renewed at comparable rates in both groups of mice, whereas the θ+ cells were more rapidly renewed in NeoTx mice than in sham‐operated littermates. In the bone marrow, the majority of both θ‐ and θ+ cells were very rapidly renewed, indicating a production of these cells in the bone marrow of ShamTx mice and also in NeoTx mice, in which the number of bone‐marrow θ+ cells was significantly higher than in ShamTx littermates.