Ultrastructural localization of 2,4-dinitrophenyl groups in mouse epidermis following skin painting with 2,4-dinitrofluorobenzene and 2,4-dinitrothiocyanatebenzene: an immunoelectron microscopical study.

The ultrastructural localization of 2,4-dinitrophenyl (DNP) groups in mouse epidermis after epicutaneous application of the contact sensitizer 2,4-dinitrofluorobenzene (DNFB) and the tolerogen 2,4-dinitrothiocyanatebenzene (DNTB) was investigated at varying times using immunoelectron microscopy with the protein A - gold technique. After application of DNFB, there was a homogenous cytoplasmic labeling of all epidermal cells. The intracellular localization of the DNP groups was not restricted to cytoplasmic organelles belonging to the endocytotic - lysosomal system. The numerous endocytotic organelles, Birbeck granules, and lysosomes of the Langerhans cells (LCs) typically observed after application of contact sensitizers also did not show an increased number of gold particles. Skin painting with DNTB resulted in a similar distribution and time-course of immunolabeling, but this compound did not induce cellular and the endocytotic activation of LCs as seen after DNFB application. These results demonstrate that contact sensitizers do not require specific cellular uptake and intracellular processing by the endocytotic - lysosomal compartment of the LCs before membrane presentation. However, a cellular and endocytotic activation of the LCs by haptens may be an important mechanism for T effector cell activation.