A comparison of the responses of lymphocytes from blood, spleen, thymus and appendix of rabbits of different ages to stimulation "in vitro" with staphylococcal filtrate.

There are lymphocytes in the spleen, appendix, thymus and peripheral blood of unimmunized rabbits which are activated to a blast state by staphylococcal filtrate. Staphylococcal filtrate-responsive cells are present in the thymus of rabbits at birth and their appearance in spleen and appendix coincides with the lymphoid ontogeny of these tissues. Thymus lymphocytes survive less well than lymphocytes from peripheral blood but the temporal relationship of their responses to staphylococcal filtrate is similar. Spleen lymphocytes survive as well as peripheral lymphocytes. Spleens of most adult rabbits contain a population of lymphocytes which responds sooner to staphylococcal filtrate, in terms of tritiated thymidine incorporation, than peripheral lymphocytes from the same animal.