Soluble human MHC class I molecules induce soluble Fas ligand secretion and trigger apoptosis in activated CD8+ Fas (CD95)+ T lymphocytes

In the present study, we have evaluated the apoptotic effect of soluble human MHC class I (sHLA-I) antigens on CD8⁺ T lymphocytes. sHLA-I antigens and β2-microglobulin-free HLA class I heavy chains, isolated from serum, induced apoptosis on phytohemagglutinin-activated CD8⁺ T lymphocytes in autologous and allogeneic combinations. The extent of CD8⁺ T cell apoptosis depends on the degree of activation, time of incubation with sHLA-I antigens and amount of sHLA-I antigens added to the cultures. Apoptosis is induced by the interaction of Fas (CD95)⁺ cells with soluble Fas ligand which is released following binding of sHLA-I antigens to CD8 molecules. These results suggest that sHLA-I antigens may regulate immune responses by inducing apoptosis in activated CD8⁺ T cells.