Dermatopathic lymphadenopathy. Electronmicroscopic, enzyme-histochemical and immunohistochemical study.

Dermatopathic lymphadenopathy (DPL) is characterized by lymph node enlargement with reactive process and is generally caused by chronic inflammatory skin disease. Interdigitating reticulum cells (IDCs) with broad cytoplasm, innumerable cytoplasmic interdigitation, and bizarre shaped nuclei are the most striking cell type in DPL. According to the shape of the nucleus, arrangement of the tubulovesicular complexes (TVC) and amount of melanin granules, these cells fall into two types: type I has a marked indented nucleus, innumerable TVC and some desmosomal junctions and fewer melanin granules, while type II has a large amount of melanin granules. On the other hand, LCs contain a few loose melanin granules. It appears that IDCs and Langerhans cells (LCs), surrounded by T-lymphocytes, are similar in morphology and function, but both of them can be characterized by the positive of S-100 protein and Leu 6, absence of lysozymes and CEA by PAP method, and positive of ATP-ase and ACP-ase, and they differ only by having or not having Birbeck granules. The mechanism of the proliferation of IDCs in DPL and delineation of the functional relationship between the accessory cells and the T-lymphocytes remains to be investigated.