Effect of Endothelial Cells on Phagocyte-mediated Anticryptococcal Activity

The anticryptococcal activity of peripheral blood polymorphonuclear leukocytes (PMN) and monocytes was compared on plastic versus human umbilical vein endothelial cell surfaces. Various amounts of PMN and monocytes were incubated on plastic or endothelial surfaces and then challenged for 18 h with Cryptococcus neoformans. Both phagocyte populations exhibited significantly more anticryptococcal activity on an endothelial cell monolayer than on plastic. Prestimulating the endothelial cell monolayer with interleukin-1 augmented the antifungal activity of PMN but not that of monocytes. In the absence of phagocytes, endothelial cells lacked activity. Blocking antibodies directed against endothelial adhesion molecules ICAM-1 and ELAM-1 did not affect PMN-mediated inhibition of fungal growth. Recombinant interleukin-1 and interleukin-8 (two cytokines secreted by endothelial cells) activated neutrophils for modestly enhanced antifungal activity. However, supernatants derived from endothelial cells, as well as neutralizing antibodies directed against the endothelial cell-derived cytokines interleukin-8 and granulocyte-macrophage colony-stimulating factor failed to augment PMN antifungal activity. PMN viability after 18 h was diminished on plastic compared with endothelial surfaces. While the percentages of C. neoformans bound to neutrophils were similar on both surfaces, the patterns of binding were markedly different: on endothelial (but not plastic) surfaces, most cryptococci were surrounded by greater than five PMN. Thus, phagocyte-mediated inhibition of cryptococcal growth is enhanced on endothelial monolayers compared with plastic surfaces, possibly as a result of differences in phagocyte viability and patterns of binding. Bolstering the activity of circulating phagocytes by stimulating endothelial cells may be of relevance in the treatment of patients with or at risk for cryptococcemia.