Thymic stromal cells eliminate T cells stimulated with antigen plus stromal Ia molecules through their cross-talk involving the production of interferon-gamma and nitric oxide.

We previously established a thymic stromal cell clone capable of inducing differentiation of immature thymocytes and described a clonal elimination model in which T cell clones are killed on the monolayer of this stromal clone by stimulation of their T cell receptors (TCR) with antigen plus stromal Ia molecules. This study investigated molecular mechanisms underlying this phenomenon. Antigenic stimulation on thymic stromal cells produced large amounts of interferon-gamma (IFN-gamma) and small amounts of tumor necrosis factor-alpha (TNF-alpha). Addition of anti-IFN-gamma monoclonal antibody (mAb) to these cultures largely prevented death of TCR-stimulated T cells. T cell death was also induced when cultures were treated with recombinant IFN-gamma (rIFN-gamma) or rTNF-alpha instead of the relevant antigen, showing that these lymphokines are involved in the process of T cell death. It was further demonstrated that these lymphokines, especially IFN-gamma, induced the expression of mRNA for the inducible type of nitric oxide (NO) synthase in thymic stromal cells and that enhanced levels of NO were produced by stromal cells cultures with T cells plus antigen or stimulated with rIFN-gamma or rTNF-alpha. NO was found to be critically responsible for inducing T cell death on the stromal cell monolayer following stimulation of T cells with antigen or of stromal cells with rIFN-gamma or rTNF-alpha, because T cells death was completely prevented by addition of NG-monomethyl-L-arginine (L-NMMA), which is capable of inhibiting NO production. These results indicate that elimination of TCR-stimulated T cells on thymic stromal monolayers with the capacity to support thymocyte differentiation is induced by the cross-talk between IFN-gamma/TNF-alpha-producing T cells and stromal cells capable of producing NO in response to these lymphokines.