Langerhans cells that express matrix metalloproteinase 9 increase in human dermis during sensitization to diphenylcyclopropenone in patients with alopecia areata.

BACKGROUND: We know little of the initial events during the sensitization phase of contact allergy in humans. Alopecia areata (AA), a disease of unknown pathogenesis characterized by patchy hair loss, may be treated by inducing contact allergy to diphenylcyclopropenone (DPC), later followed by its topical application.

OBJECTIVES: To learn more about the initial events during sensitization in human skin, we studied the early events during induction of contact allergy to DPC in patients with AA.

METHODS: DPC 2% and sodium lauryl sulphate (SLS) 4% were applied on the backs of eight patients with AA. Punch biopsies were taken 6 and 24 h after application. The biopsies were snap-frozen and cryostat sections were evaluated with immunohistochemistry using antibodies against CD1a, HLA-DR, CD3, CD54 and matrix metalloproteinase 9 (MMP-9).

RESULTS: After 24 h all subjects exhibited erythema on the DPC-treated areas. Histological evaluation of biopsies from these areas showed hydropic degeneration and a significantly increased number of MMP-9+ cells in the dermis (P < 0.0005). The MMP-9+ cells were identified with double immunofluorescence staining as CD1a + Langerhans cells. The expression of the other markers studied remained unaltered irrespective of treatment, including treatment with SLS.

CONCLUSIONS: Our findings show that DPC induces an irritant reaction leading to an increased number of MMP-9+ CD1a+ cells in the dermis during the initial phase of sensitization.