Down‐modulation of CD4+ T helper type 2 and type 0 cells by T helper type 1 cells via Fas/Fasligand interaction

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Abstract
Fas was recently demonstrated to be the major target molecule engaged by CD4+ cytolytic T lymphocytes (CTL). We examined Fas expression on various cloned T cell subpopulations and their susceptibility to lysis by CD4+ or CD8+ CTL. A reciprocal relationship in Fas and Fas‐ligand expression was observed in CD4+ T helper (Th)1‐ and Th2‐type clones, and Fas mRNA was predominantly detected in Th2 clones, whereas Fas‐ligand mRNA was principally found in Th1 clones. The two Th0 clones tested expressed both Fas and Fas‐ligand, but only one exhibited cytolytic activity, whereas both were sensitive to CD4‐mediated lysis. A functional consequence of the inverse Fas‐Fas‐ligand expression pattern was that Th2 and Th0 cells were sensitive to lysis by both Th1 CD4+ CTL and a CD8+ CTL clone in a Fas‐dependent manner. These results suggest that cytolytic CD4+ Th1 cells may play an immunomodulatory role, regulating a Th2/Th0 response by Fas‐mediated lysis.