The hapten in contact hypersensitivity to dinitrochlorobenzene: immunoelectron microscopic and immunofluorescent studies.

Six hours after challenge with dinitrochlorobenzene (DNCB) in sensitized volunteers, infrequent cells reacting with both OKT6 (CD 1a) and with an antibody to DNCB were demonstrated in the upper dermis in 3 out of 4 subjects, using a double fluorescence technique. Single marker studies using polyclonal and monoclonal antibodies to DNCB showed cytoplasmic reactivity with peripheral accentuation in keratinocytes throughout the epidermis, most intense in the granular and basal layers, and occasional positive cells in the papillary dermis. Immunoperoxidase electron microscopy using polyclonal and monoclonal antibodies to DNCB demonstrated reactivity on keratinocyte and Langerhans cell membranes, with intracellular deposition of reaction product on mitochondria. Reaction product was present on the external leaflets of Birbeck granules, suggesting that the penetration of DNCB was passive rather than due to an active endocytic process. The immunofluorescent studies suggest that the double-fluorescing upper dermal cells were Langerhans cells but this could not be confirmed by electron microscopy.