Phenotypic characterization of the early cellular responses in allergic and irritant contact dermatitis

Despite qualitative similarities there were subtle differences between the nickel allergic and dithranol irritant dermatitis reactions. In both responses, dermal and epidermal cellular infiltrates developed, which were predominantly of Leu 3a phenotype with lesser numbers of Leu 2a positive cells. Dermal infiltrates were larger in the allergic response, but epidermal invasion was greater in the irritant reaction. In the allergic challenge response, Leu 3a reactive cells appeared in the dermis and epidermis by 4 h. At 48 h, both reactions showed skin infiltration by Leu M3 positive macrophages, and had increased numbers of cells in the epidermis expressing class II antigens. The number of Leu 6 reactive Langerhans cells in the epidermis was almost halved at 48 h in the irritant reaction, but Langerhans cell counts were increased by a third between 24 and 48 h of the allergic response. Ultrastructural studies showed disruption of the Langerhans cell mitochondrial cristae at 8 h in the irritant reaction, with few identifiable epidermal Langerhans cells at 48 h. At 1 h in the allergic response, electron microscopy identified two populations of Langerhans cells; the majority showed an electron-dense cytoplasm with vacuoles, and the rest appeared normal. Peripolesis was noted in both types of reaction.