I-A-positive nonlymphoid cells and T cell development in murine fetal thymus organ cultures: interleukin 1 circumvents the block in T cell differentiation induced by monoclonal anti-I-A antibodies.

A fetal thymus organ culture system has been used to monitor the influence of interleukin 1 (IL 1) on the production of functional T cells as assessed by cell recoveries and MLC assays. We had shown earlier that the addition of monoclonal anti-I-A antibody inhibited the development of functional T cells as well as the expression of Ia on nonlymphoid cells recovered from fetal thymus organ cultures. The addition of purified recombinant IL 1 to anti-I-A-treated cultures reversed the inhibition of T cell growth induced by anti-I-A. IL 1 also induced the reexpression of Ia on the surfaces of nonlymphoid cells that could be recovered from the cultures. The "rescue" effect of IL 1 on anti-I-A-treated fetal thymus lobes was manifested in spite of the fact that the addition of IL 1 to untreated cultures had little effect on T cell development. To determine if IL 1 had a physiologic role in the development of the fetal thymus in organ culture, highly specific goat antibodies to IL 1 were added to organ cultures. These antibodies inhibited the development of T cells in organ cultures as determined by cell recovery and MLC reactivity. These results are consistent with the conclusion that IL 1 is an important mediator in the growth and development of functional T cells in the fetal thymus.