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.