Letterer-Siwe disease: immunopathologic study with a new monoclonal antibody.

Three cases of Letterer-Siwe disease were studied with the monoclonal antibody Lag, which reacts to the antigen on the membranes of Birbeck granules and related structures of human Langerhans cells. Both lymph nodes and lesional skin contained abundant Lag-positive cells. By two-dimensional gel electrophoresis, antigenic substances in the lymph nodes of patients with Letterer-Siwe disease were found to have the same molecular weight of 40,000 dalton and isoelectric points extending from 4.7 to 6.5 as those in normal human skin and lymph nodes. Our results support the contention that Letterer-Siwe disease is a proliferative disorder of Langerhans cells. A double-staining method with Lag and anti-T6 antibody revealed that Lag reacted to 70% of T6-positive cells in the lymph nodes but to almost all such cells in skin lesions of patients with Letterer-Siwe disease, suggesting that the proliferating cells consist of at least Lag+, T6+, and Lag-, T6+ subpopulations.