In contrast, CD4+CD25+ T cells did not regulate hapten-specific CD8+ T-cell priming and CHS responses initiated by Fas-defective (lpr) DC. Thus, restricting DC priming functions through Fas–FasL
interactions is a potent mechanism employed by CD4+CD25+ regulatory cells to restrict CD8+ T-cell-mediated allergic immune responses in the skin. The development of antigen-specific effector T cells during the induction of immune responses must be tightly regulated to prevent excessive damage of tissues and organs. Recent studies have identified elimination of APC, including DC and B cells, as an important mechanism restricting T-cell-mediated immune responses 1–4. Several studies have reported that APC elimination is mediated through apoptosis induced by CD4+ T cells reactive to antigen/class II MHC complexes presented by DC 2, 3, 5. ATM/ATR activation Importantly, Fas-mediated elimination of DC has been recently implicated as a mechanism regulating the initiation of autoimmune responses 4. The role of this mechanism in regulating priming of T cells to exogenous antigens remains unclear. Contact hypersensitivity
(CHS) is a skin allergy that is the most frequently observed dermatosis in industrialized countries 6. CHS responses occur in response to epicutaneous sensitization and challenge with haptens including urushiol, 2,4-dinitrofluorobenzene (DNFB) and oxazolone 7, 8. These responses are mediated by IFN-γ and IL-17-producing selleck chemicals CD8+ T cells primed by hapten-presenting Langerhans cells (hpLC) and dermal DC migrating from the sensitized skin to the draining LN 9–12. The numbers and persistence of hapten-presenting DC in these LN during effector T-cell priming is restricted through Fas–FasL interactions 1. Although CD4+ T cells are not required to mediate CHS as effector or helper cells, regulatory CD4+CD25+ T cells restrict hapten-specific
CD8+ T-cell expansion for CHS responses 13, 14. Whether the role of Fas–FasL-mediated regulation is associated with CD4+CD25+ T cells remains untested. Two approaches were used to directly test whether these regulatory T cells induce FasL-mediated DC apoptosis to limit the duration of antigen presentation and expansion of the CD8+ effector T cells in CHS responses. First, the impact of CD4+CD25+ T cells on the survival of hapten-presenting DC in Astemizole the LN priming site was evaluated in vivo and the ability of these regulatory T cells to enhance FasL-mediated apoptosis of hapten-presenting DC was tested in vitro. Second, Fas-sufficient (WT) and Fas-defective (lpr) DC were compared for induction of CD8+ T-cell and CHS responses and the potential influence of CD4+CD25+ T cells on the priming capabilities of these DC was tested. The results strongly support the hypothesis that CD4+CD25+ T cells regulate CD8+ T-cell-mediated immune responses in the skin by inducing FasL-mediated apoptosis of skin-derived antigen-presenting DC.