Regulation of the immune response by subclasses of T lymphocytes. II. The effect of adult thymectomy upon humoral and cellular responses in mice

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Abstract
The immunologic consequences resulting from thymectomy in adult lifewere investigated. Primary humoral responses were not diminished shortlyafter adult thymectomy, as judged by responses of intact thymetomized mice as well as by the ability of spleen cells from such mice to transfer primary responses. However, secondary humoral responses were substantially reduced in irradiated recipients of spleen cells from primed adult-thymectomized mice, suggesting that the thymus is required in adultlife to maintain a population of cells important in the generation of immunologic helper memory. By contrast, small doses of anti- thymocyte serum, which primarily affect recirculating T cells, abrogated the printary humoral response, but allowed the subsequent development of immune memory. Using a technique permitting in vitro sensitization of purified T cells to alloantigens, it was shown that adult thymectomy increasesthe ability of T cells to generate primary cytotoxic responses, but had little effect upon the development of cytotoxic T memory activity. Theseexperiments suggest that in adult life the thymus maintains a regulatorypopulation of T cells in peripheral tissues which suppress early T cell differentiation to cytotoxic effector cells and potentiates the development of immune memory.