Immunohistology and aetiology of histiocytic necrotizing lymphadenitis. Report of three instructive cases.

Three cases of histiocytic necrotizing lymphadenitis are reported. Two patients came from Vietnam and the third from Greece. In all cases there was infection with yersinia enterocolitica of serogroup 9 or 3. Cervical lymph nodes were examined. Histologically, the characteristic necrosis developed in large foci of so-called T-associated plasma cells. Immunological analysis showed that these cells have characteristic markers of helper/inducer T cells, but do not express sheep erythrocyte receptors. The T-associated plasma cells perished by pyknosis and were then phagocytosed and digested by macrophages, which were present in large numbers. The necrotic areas were exclusively located in hyperplastic T regions. The B-cell system did not play a role in the reaction. T-associated plasma cells have been renamed 'plasmacytoid T cells' because they contain abundant rough endoplasmic reticulum ('plasmacytoid') and show immunological features of T cells. It appears likely that plasmacytoid T cells are the counterparts of plasma cells of the B-cell system that secrete lymphokines instead of immunoglobulin.