DIFFERENTIAL ABILITY OF T(H)1 AND T(H)2 T-CELLS TO EXPRESS FAS LIGANDAND TO UNDERGO ACTIVATION-INDUCED CELL

Stimulation of previously activated T cells through the antigen recept or can result in the apoptotic death of the responding cell, a process referred to as activation-induced cell death (AICD). This process app ears to involve Fas (CD95) and its ligand (Fas-L). The distribution of Fas and Fas-L on Various T cell subsets has not been extensively char acterized. We have therefore analyzed cells committed to a T(h)1- or T (h)2-type differentiation pattern for the expression and function of F as-L. Using both a sensitive bioassay and flow cytometry, we demonstra te that cloned T(h)1 cells express high levels of Fas-L, whereas clone d T(h)2 cells express only low levels. The expression of Fas-L by T(h) 1 and T(h)2 cells correlates with the relative abilities of these two cell types to undergo AICD. Whereas AICD is readily observed in cultur es of cloned T(h)1, but not T(h)2, cells, T(h)2 cells are capable of u ndergoing apoptosis in the presence of T(h)1 cells expressing Fas-L. T he ability of T cells to undergo AICD appears to be unrelated to the p resence of various cytokines. Thus, the Fas/Fas-L pathway appears to b e critical for the induction of AICD and this pathway is differentiall y regulated in cells committed to either T(h)1 or T(h)2 differentiatio n.