The role of human epidermal Langerhans cells in skin immunity.

Of the occupational dermatoses, contact dermatitis is the most frequent. And the afferent limb of the antigen-specific delayed type hypersensitivity reaction seen in allergic contact dermatitis is induced by epidermal Langerhans cells (Lc). HLA-DR-positive Lc are probably the most important cells, capable of providing the initial alo-activating signal for skin graft rejection, and act as antigen-presenting cells for T cells, both with contact and microbial antigens, suggesting that they produce Interleukin 1. The amount of HLA-DR determinants is 50-100 times higher on Lc than on blood derived adherent cells, and they are more potent in inducing some antigen-specific T-cell responses. These antigen-specific T-cell responses are also restricted by HLA-D/DR antigens. UVB-radiation of Lc or preincubation with glucocorticosteroids reduces in a dose-dependent manner the Lc-induced T-cell responses to antigens.