Myeloperoxidase expression by histiocytes in Kikuchi's and Kikuchi-like lymphadenopathy

Forty-five examples of Kikuchi's lymphadenitis (KL), 5 Kikuchi-like lupus e rythematosus lymphadenopathies, 25 nonnecrotizing lymphadenitidies (5 toxop lasmic, 5 sarcoid-like, 6 dermatopathic, 4 suppurative, 3 tubercular, 2 wit h sinus histiocytosis), 4 examples of hyaline-vascular Castleman disease CD , 2 plasmacytoid monocyte tumors (PM-Ts), and 61 accessory cell neoplasms w ere studied by a panel of antibodies, including the PG-M1 (against a macrop hage-restricted CD68 epitope) and a polyclonal antimyeloperoxidase (MPO). I n KL and Kikuchi-like lupus erythematosus lymphadenopathies, 25 to 75% of C D68(+) histiocytes co-expressed MPO. This did not occur in nonnecrotizing l ymphadenitidies and accessory cell neoplasms. MPO+/CD68(+) elements corresp onded to nonphagocytosing mononuclear cells and some crescentic macrophages and phagocytosing histiocytes. Typical PMs were MPO-/CD68(+) in all cases, including CD and PM-T. Our observations suggest that in KL and KL-like lym phadenopathies: 1) MPO+/ CD68(+) blood monocytes might be attracted into ti ssues because of the lack or paucity of granulocytes and the need of MPO fo r oxidative processes; 2) PMs are more likely to be involved in the cytotox ic immune reaction than in phagocytic phenomena; 3) the peculiar phenotype of the histiocytic component can be usefully used for the differentiation f rom malignant lymphoma and PM-T.