Neonatal thymectomy identifies two major pools of sessile and recirculating peripheral T cells which appear to be under separate homeostatic control.

In this study the role of the thymus in the development of sessile T cell populations resident in spleen and lymph nodes (LN) was contrasted with the development of recirculating T cell populations trafficking between blood and lymph. Extensive analysis of the composition and the rate of growth of the secondary lymphoid tissues and recirculating lymphocyte pool coupled with neonatal thymectomy revealed that the sessile and recirculating T cell populations showed different degrees of thymic dependency and increased in size at different rates, suggesting these two populations might be under separate homeostatic control. Neonatal thymectomy also resulted in a much greater depletion of CD8+ and gammadelta TCR+ T cell subsets compared with CD4+ T cells in the sessile and recirculating T cell pools, and greatly reduced the number of T cells homing to peripheral lymph nodes compared with those homing to the gut.