Alopecia areata and universalis in the Smyth chicken model for spontaneous autoimmune vitiligo.

The Smyth line (SL) chicken model for spontaneous, postnatal expression of vitiligo may also show varying incidences and degrees of severity ranging from alopecia areata-like to universalis-like integumental changes. Although human vitiligo patients are known to have a four times greater chance of having alopecia areata than do people without vitiligo, in the SL model, feather loss is limited to birds that show some degree of amelanosis of feather and skin tissue. Both the vitiligo and the alopecia have an autoimmune component, as shown by histologic and immunologic studies, including the correctional influences of corticosterone and cyclosporine-A. The major histocompatibility haplotype (MHC) has a major effect on the incidence and expression of the vitiligo, as well as the alopecia that occurs within vitiliginous birds. Three different MHC haplotypes were identified in the original line that was selected for vitiligo, and from these, three sublines were developed, each homozygous for a different haplotype. Of the three sublines (SL101, SL102, and SL103) the vitiligo has a significantly earlier onset and severity 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 component for the alopecia trait. It is hypothesized, but as yet unproven, that a feather development defect interacts with the SL melanization and immunologic defects to initiate the partial (areata) and complete (universalis) alopecias. The alopecia universalis is rarely seen until adulthood and is characterized by short (<0.5 cm), undeveloped feathers. If feather growth resumes in these birds, the feathers dry up, cease to grow, and often break off.