Alopecia areata and universalis in the Smyth chicken model for spontaneousautoimmune vitiligo

The Smyth line (SL) chicken model for spontaneous, postnatal expression of vitiligo may also show varying incidences and degrees of severity ranging f rom alopecia areata-like to universalis-like integumental changes. Although human vitiligo patients are known to have a four times greater chance of h aving alopecia areata than do people without vitiligo, in the SL model, fea ther loss is limited to birds that show some degree of amelanosis of feathe r and skin tissue. Both the vitiligo and the alopecia have an autoimmune co mponent, as shown by histologic and immunologic studies, including the corr ectional influences of corticosterone and cyclosporine-A, The major histoco mpatibility haplotype (MHC) has a major effect on the incidence and express ion of the vitiligo, as well as the alopecia that occurs within vitiliginou s birds. Three different MHC haplotypes were identified in the original lin e that was selected for vitiligo, and from these, three sublines were devel oped, each homozygous for a different haplotype. Of the three sublines (SL1 01, SL102, and SL103) the vitiligo has a significantly earlier onset and se verity in the SL101 than in the other two Lines. The incidence of alopecia, however, is significantly lower in the SL101 subline than in the other two , Inheritance of the vitiligo is polygenic with an additional genetic compo nent for the alopecia trait. It is hypothesized, but as yet unproven, that a feather development defect interacts with the SL melanization and immunol ogic defects to initiate the partial (areata) and complete (universalis) al opecias, The alopecia universalis is rarely seen until adulthood and is cha racterized by short (<0.5 cm), undeveloped feathers, If feather growth resu mes in these birds, the feathers dry up, cease to grow, and often break off .