[Typing of infiltration cells in primary, localized, nodular, cutaneous amyloidosis].

Amyloid tumours in two patients with primary localized nodular cutaneous amyloidosis contained very dense infiltrates consisting mainly of plasma cells and lymphocytes. In one case IgM was detected on many cells of the infiltrate, while in the other IgA was found in morphologically apparently normal plasma cells. Immunohistochemical investigations did not reveal any immunoglobulin light chain restriction in either of the tumours. Numerous cells expressed B cell markers, such as CD20 or CD38. Rearrangement studies on material from the amyloid tumour of one of the patients confirmed the monoclonality of plasma cells. This observation indicates that the nodules of primary localized nodular cutaneous amyloidosis indeed represent an extramedullary plasmocytoma, which consists of amyloid-producing plasma cells. Of special interest was the unexpectedly high proportion of cells expressing T cell markers (CD3, CD5, CD4 greater than CD8) in the amyloid nodules of both patients. After excluding co-expression of B and T cell markers on identical cells by immunohistochemical studies on serial sections and also after molecular biological studies, we assume that this is a separate T cell population that may have a regulatory effect on the production of amyloid.