ENDOTHELIAL-CELLS POTENTIATE OXIDANT-MEDIATED KUPFFER CELL PHAGOCYTICKILLING

Phagocytosis and killing of circulating organisms by Kupffer cells (KC s) are discrete, important components of host defense. However, the ki lling mechanism(s) are not fully understood, and the potential role of adjacent nonparenchymal cells such as hepatic endothelial cells has n ot been defined. Rat KCs -/+ an hepatic endothelial cell enriched cell ular fraction (HECEF) were incubated with Candida parapsilosis and ass ayed for phagocytosis and phagocytic killing by validated fluorochroma tic vital staining. The role of reactive oxygen metabolites in KC phag ocytic functions was examined by inhibition with superoxide dismutase and/or catalase. Diphenyleneiodonium and allopurinol were used to exam ine the potential roles of NADPH oxidase and xanthine oxidase, respect ively, in generating these toxic oxidants. Coculture with HECEF increa sed KC phagocytic activity (from 75% to 88%) and candidacidal activity (from 20% to 31%). Superoxide dismutase, catalase, diphenyleneiodoniu m, or allopurinol caused inhibition of candidacidal activity, but did not affect phagocytosis, and did not block the potentiation of phagocy tosis or of killing caused by coculture with HECEF. Reactive oxygen in termediates generated by both NADPH oxidase and xanthine oxidase-depen dent pathways are important in KC killing of Candida parapsilosis. In vitro, KC phagocytosis and killing are potentiated (via a non-oxidant- mediated mechanism) by coculture with a preparation of hepatic non-par enchymal cells composed primarily of endothelial cells. (C) 1998 Elsev ier Science Inc.