| The Smyth line (SL) chicken is an animal model to study human vitiligo. Vitiligo in SL chickens is characterized by post-hatch loss of feather melanocytes (MC) resulting in feather depigmentation. Like in humans, the etiopathology of SL vitiligo (SLV) is not well defined. Based on previous studies, we hypothesized that cell-mediated immunity (CMI) plays an important role in SLV. Using vitiliginous SL and normally pigmented MHC-matched parental Brown line (BL) and Light Brown line (LBL) chickens (controls), several studies were conducted to provide direct evidence for this hypothesis. Included were (1) examination of the delayed wattle response (DWR, in vivo CMI response) to embryo- or feather-derived MC lysates, (2) determination of IFNγ expression and production in feathers by Northern blotting and immunoblotting analyses, and (3) determination of whether an apoptotic mechanism is involved in MC death using TUNEL assay and immunofluorescence staining of feather sections. It was found that vitiliginous SL chickens exhibited a significantly greater DWR to feather-MC than controls and non-vitiliginous SL chickens. This DWR peaked at 3 to 5 days, and was associated with the infiltration of primarily T cells (TCR2+, CD4+ and CD8+ T cells) into the injection site. IFNγ was detected in feather samples where depigmentation was in progress, whereas, prior to noticeable depigmentation or after complete depigmentation, IFNγ expression was greatly reduced or nearly undetectable. In the feathers of control chickens. IFNγ was not detected.{09}The number of TUNEL+cells primarily in the epithelial barb ridge where MC cell bodies are located, was significantly higher in vitiliginous SL chickens than controls. The extent of this apoptosis varied with the severity of depigmentation (i.e., highest in active vitiligo), suggesting a close association between apoptosis and the disappearance of MCs. In addition, infiltration of CD8+ cells into the epithelial barb ridge was associated with enhanced apoptosis, and some of these CD8+ cells were localized next to the TUNEL+ cells. Collectively, these studies demonstrated that SLV chickens have MC-specific CMI in vivo and that MC death in the feather involved a Th1-dominated response and apoptosis, apparently mediated by cytotoxic T cells. |
