Evidence in favor of a role for Langerhans cells in contact allergic hypersensitivity reactions has been reviewed. This includes mononuclear cell to Langerhans cell apposition and damage to some Langerhans cells at sites of specific challenge to a variety of contact allergens. Such apposition occurs in actively sensitized patients and guinea pigs and in passively sensitized guinea pigs. In addition, in passively sensitized guinea pigs Langerhans cells circulate in dermal vessels resembling lymphatics and are much increased in the dermis after challenge with the contact allergen. These observations, together with the existing knowledge that Langerhans cells occur in the lymph nodes and thymus, suggest that these cells may be involved not only in contact allergic reactions but also in other immunologic reactions, particularly in cell-mediated reactions in the skin.

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