Effects of thymectomy, thoracic duct drainage, and radiation on T and B lymphocyte distribution and cardiac allograft survival in rats

The effects of several widely used lymphoid ablative procedures designed to deplete rats of T lymphocytes have been examined. These studies emphasize both the distribution of T and B lymphocytes in individual host lymphoid compartments and the survival of cardiac allografts in recipients modified by various means. Adult thymectomy reduced the numbers of T lymphocytes in the thoracic duct (TD) and lymph nodes and to a lesser extent in the spleen, but did not alter circulating T cell numbers or cardiac graft survival. TD drainage performed alone or in combination with adult thymectomy reduced circulating T cells but did not prolong graft survival. In contrast, indefinite cardiac survival occurred in “B” rats, animals undergoing adult thymectomy, total body irradiation, and reconstitution with syngeneic bone marrow cells from TD-drained donors. However, B rats were not only profoundly depleted of T cells but also of B cells. Infinite graft survival in these recipients appears to represent a true immunological deficit since passive transfer of cells and sera from B rats with long-term surviving grafts failed to influence survival of test heart grafts in unmodified syngeneic recipients. Additionally, thymocytes, lymphoid cells, and TD cells from unsensitized rats or splenocytes from sensitized rats restored the capacity of the B recipient to reject their grafts acutely. Thus, operative manipulations required to obtain profound depletion of T cells not only may result in prolonged cardiac graft survival but may also cause significant depletion of certain B cells. The less extensive ablative procedures of adult thymectomy or TD drainage only decrease T cells in selected compartments in rats; however, distribution of the effected T cells differ from those previously reported in mice undergoing similar procedures.