Evasion of myofibroblasts from immune surveillance: a mechanism for tissue fibrosis.

Tissue fibrosis evolving from impaired tissue remodeling after injury is characterized by myofibroblast accumulation. We propose that during the development of fibrosis myofibroblasts acquire an immune-privileged cell phenotype, allowing their uninterrupted accumulation. Using the murine model of bleomycin-induced lung fibrosis in mice, we show that myofibroblasts that accumulate in lungs with fibrosis, but not in normal lungs, kill Fas(+) lymphocytes, resist Fas-induced apoptosis, and survive longer when grafted into allogeneic mice. In contrast, bleomycin-treated FasLigand (FasL)-deficient (gld) chimeric mice did not accumulate myofibroblasts or collagen in their lungs, and their FasL(-) myofibroblasts did not survive after alloengraftment. This finding indicates that myofibroblasts possess Fas/FasL-pathway-dependent characteristics that allow them to escape from immune surveillance and resulting organ fibrosis.