Fas-mediated inhibition of CD4+ T cell priming results in dominance of type 1 CD8+ T cells in the immune response to the contact sensitizer trinitrophenyl.

One of the unusual properties of chemically reactive haptens is their capacity to simultaneously generate immunogenic determinants for hapten-specific CD8(+) and CD4(+) T cells. Surprisingly, however, a clear dominance of CD8(+) effector T cells is observed in murine contact hypersensitivity to various haptens and upon T cell priming with hapten-modified APCs in vitro. In this study we show that trinitrophenyl-specific CD8(+) T cells actively prevent CD4(+) T cell priming in vitro. This process requires cell-cell contact and is dependent on the expression of Fas on the CD4(+) T cells. Our results reveal an important Fas-dependent mechanism for the regulation of hapten-specific CD4(+) T cell responses by CD8(+) T cells, which causes the dominance of CD8(+) effector T cells and the active suppression of a CD4(+) T cell response. Moreover, our demonstration of reduced contact hypersensitivity to trinitrophenyl in the absence of Fas, but not of perforin and/or granzymes A and B, underlines the important role of Fas as a pathogenetic factor for contact hypersensitivity.