Strong expression of CD40, CD54 and HLA-DR antigen and lack of evidence for direct cellular cytotoxicity are unique immunohistopathological features in alopecia areata.

The pathological role played by T cells infiltrating hair follicles in lesions of alopecia areata (AA) is unknown. We examined the expression in cryostat sections of scalp skin obtained from a total of 28 patients with AA and from five normal control subjects of (1) molecules related to the induction of cell death including Fas, Fas ligand (FasL), perforin, granzyme B (GB), and TIA-1, (2) molecules related to antigen presentation including CD1a, CD40, CD54, CD80, and CD86, and (3) molecules induced by interferon gamma (IFN-gamma) including CD40, CD54, Fas, and HLA-DR. CD3(+) T cells infiltrated perifollicularly, perivascularly and in the hair structure and there was a predominance of CD4(+) over CD8(+) cells. Antigen-presenting cells expressing CD1a, CD40, CD54, or HLA-DR were also seen. Expression of CD40, CD54, HLA-DR and CD95 was also seen in the hair structure including the dermal papilla. Consistent with these observations, IFN-gamma-producing cells were also detected in the perifollicular infiltrate. In contrast, few Fas-L(+), perforin(+), GB(+) or TIA-1(+) cells were found adjacent to the follicles. Apoptotic cells were recognized only in the outer root sheath of catagen hairs. These findings suggest that infiltrating T cells interact with perifollicular or follicular antigen-presenting cells to produce IFN-gamma, which deprives dermal papilla cells of their ability to maintain anagen hair growth.