Immunohistochemical monitoring of plasmacytoid cells in lymph node sections of Kikuchi-Fujimoto disease by a new pan-macrophage antibody Ki-M1P.

The new monoclonal antibody Ki-M1P, which detects a formalin-resistant epitope on conventional paraffin sections, was applied in 20 cases of different stages of Kikuchi-Fujimoto disease. This new pan-macrophage immunoreagent detects plasmacytoid T cells, referred to as plasmacytoid cells, and renders a reliable delineation of these cells against other similar cell types, such as blasts of high-grade B- and T-cell lymphoma. Histiocytes as well as macrophages were strongly positive, and plasmacytoid cells showed a somewhat weaker and primarily granular, intracytoplasmic immunoreactivity. Plasmacytoid cells, being a diagnostic feature of the Kikuchi-Fujimoto disease, facilitate a clear distinction of this disease entity from large cell or high-grade lymphomas. These results may represent an additional argument favoring the histiocytic origin of plasmacytoid cells. Additionally, they may point to an immunohistochemical tool that facilitates the differential diagnosis between Kikuchi-Fujimoto disease, especially in early stages of the disease, and malignant lymphoma.