Rat thymus reconstitution after thymocyte destruction by glucocorticoid treatment--from the view of endogenous DNA synthesis and soybean lectin responsiveness in thymocytes

The dynamic process in rat thymocyte restoration after their destruction by glucocorticoid (GC) administration was examined. Thymus weight and thymocyte count became minimal 4-5 days after the administration. Then the thymus took a course of recovery. Endogenous DNA synthesis in thymocytes, reflecting their proliferation within thymus, decreased for 4 days but began to increase 6-8 days after GC treatment. Thymocyte responsiveness to soybean lectin (SBL), a possible stimulator for T-cell-precursors, showed elevation 4-5 days after the treatment. A marked decrease of lymphocytes in the cortex and unclearness of cortico-medullary junction were observed 2-3 days after GC treatment. Clusters of small lymphoid cells, which possibly contained SBL-responding cells, were found in the subcapsular area 4 days after the treatment and successively, large lymphocytes became visible in the same area. Thereafter, small lymphocytes in the cortical mid and deep zones increased, and cortico-medullary junction was restored. These histological features are discussed from the view of correspondence with the dynamic changes of endogenous DNA synthesis and SBL responsiveness in the thymocytes after GC administration.