Objective: The goals of this study were to assess morphologically the DNCB effect on Langerhans cells in the epidermis at different time intervals and to devise an in vivo test for characterization of immunoreactivity of Langerhans cells and thus of the whole skin. Methods: Reactivity of Langerhans cells (LCs) at different time intervals after the application of 0.1 % 2,4- -dinitrochlorobenzene (DNCB) on the skin of 20 volunteers was studied. Skin biopsy specimens were investigated 1, 3, 10, 30 minutes and 72 hours after DNCB application. Results: The dendrites underwent similar morphological changes as the bodies of Langerhans cells and the ultrastructural composition of the former also reflected cell activation. Other investigators did not previously pay attention to the dendrites. Our findings confirm formation of Birbeck granules (Bgs) resulting from ligand-receptor mediated endocytosis, most evident in group II where LCs showed more rapid and more vigorous activation and Bgs connected to the plasma membrane were detected in both dendrites and cell bodies. Furthermore, Birbeck granule-like structures were found in group II LCs dendrites. They reflect enhanced reactivity of these cells that do not represent a different type of LCs. A majority of the intracellular MHC class II molecules were found in vesicular structures, the so-called MHC-II compartment (MIIC). Simultaneously with Bgs, MIIC compartments develop in the cytoplasm and are most abundant at the moment when LCs leave the epidermis. Conclusions: We found that within 30 minutes after DNCB application, skin reactivity can be assessed, since at that interval the activation of Langerhans cells is fully completed. We suppose that the DNCB concentration used is sufficient for testing activation of Langerhans cells and at the same time no harm to the patient is to be expected. The use of biopsy needles of a small diameter is safe since the puncture affects only the epidermis and the upper layer of the corium and thus the use of local anaesthesia can be avoided.

        Key words: human skin, Langerhans cells (LCs), Birbeck granules (Bgs), 2,4-dinitrochlorobenzene (DNCB).