Role of Fas/Fas ligand-mediated apoptosis in murine contact hypersensitivity

Abstract

Apoptosis plays an important role in immune responses, but little is known about its involvement in contact hypersensitivity (CH). In this study, we have investigated the role of Fas/Fas ligand (FasL)-mediated apoptosis in the pathogenesis of CH. Mice were sensitized by one topical application of 100 μl of 3% oxazolone to shaved skin of the abdomen. Six days later, CH was provoked by challenging both sides of sensitized mouse right ear with 15 μl of 1% oxazolone. Using a DNA ladder assay, we found that apoptosis was induced in the skin of oxazolone-sensitized mice 24–96 h after allergen challenge. Annexin V-fluorescein isothiocyanate (FITC)-propidium iodide (PI) apoptosis flow cytometric assay showed that early apoptotic CD4 + T cells (annexin V-FITC +PI −), but not late apoptotic CD4 + T cells (annexin V-FITC +PI +), increased in the inflamed skin of mice with CH. Moreover, the expressions of mRNAs for T helper (Th2) cytokine (interleukin (IL)-4), Th1 cytokine (interferon (IFN)-γ) and proapoptotic molecules (Bax, Fas, FasL and IL-1β-converting enzyme (ICE)/caspase-1) were significantly elevated in the oxazolone-sensitized mouse skin 6–72 h after allergen challenge. Dramatic increase in IL-10 mRNA was only observed in the sensitized mouse skin 6 and 12 h after allergen challenge. Furthermore, CH was significantly inhibited with decreased apoptosis and early apoptotic CD4 + T cells in inflamed skin in Fas mutant lpr/ lpr mice compared to wild-type mice, whereas there were no significant differences in IL-4, IFN-γ, IL-10, Bax and ICE mRNAs in the inflamed skin of CH between lpr/ lpr and wild-type mice. Our results thus suggest that Fas/FasL pathway partially contributes to apoptosis in murine CH and that Fas/FasL-mediated apoptosis plays a partial role in the development of CH. The contribution of Fas/FasL-mediated apoptosis to CH appears independent of Th1 and Th2 cytokines.