Infections due to Cryptococcus neoformans are common in AIDS patients. We investigated the effect of chloroquine, which raises the pH of phagolysosomes, on the anticryptococcal activity of mononuclear phagocytes. C. neoformans multiplied within monocyte-derived macrophages (MDM) in the absence of chloroquine but were killed with the addition of chloroquine. Ammonium chloride was also beneficial, suggesting that effects were mediated by alkalinizing the phagolysosome. Chloroquine inhibits growth of other intracellular pathogens by limiting iron availability. However, chloroquine-induced augmentation of MDM anticryptococcal activity was unaffected by iron nitriloacetate, demonstrating that chloroquine worked by a mechanism independent of iron deprivation. There was an inverse correlation between growth of C. neoformans in cell-free media and pH, suggesting that some of the effect of chloroquine on the anticryptococcal activity of MDM could be explained by relatively poor growth at higher pH. Chloroquine enhanced MDM anticryptococcal activity against all tested cryptococcal strains except for one large-capsule strain which was not phagocytosed. Positive effects of chloroquine were also seen in monocytes from both HIV-infected and -uninfected donors. Finally, chloroquine was therapeutic in experimental cryptococcosis in outbred and severe combined immunodeficient mice. Thus, chloroquine enhances the activity of mononuclear phagocytes against C. neoformans by ironindependent, pH-dependent mechanisms and is therapeutic in murine models of cryptococcosis. Chloroquine might have clinical utility for the prophylaxis and treatment of human cryptococcosis. (

We studied the receptors on human cultured macrophages (MO-MO)

Tumor necrosis factor alpha (TNF-ox) is a key mediator of inflammation and may promote human immunodeficiency virus replication in latently infected cells. Since cryptococcosis often is associated with aberrations in the host inflammatory response and occurs preferentially in persons with AIDS, we defined the conditions under which human leukocytes produce TNF-a when stimulated by Cryptococcus neoformans. Peripheral blood mononuclear cells (PBMC) produced comparable amounts of TNF-ot following stimulation with C. neofonnans and lipopolysaccharide. Detectable TNF-ot release in response to C. neoformans occurred only when fungi with small-sized capsules were used and complement-sufficient serum was added. Fractionation of PBMC established that monocytes were the predominant source of TNF-ot. TNF-a gene expression and release occurred significantly later in PBMC stimulated with C. neoformans than in PBMC stimulated with LPS. C. neoformans was also a potent inducer of TNF-o from freshly isolated bronchoalveolar macrophages (BAM). Upon in vitro culture, BAM and monocytes bound greater numbers of fungal cells, yet their capacity to produce TNF-a following cryptococcal stimulation declined by 74 to 100%. However, this decline was reversed if the BAM and monocytes were cultured with gamma interferon. These data establish that C. neoformans can potently stimulate TNF-ox release from human leukocytes. However, several variables profoundly affected the amount of TNF-a released, including the type of leukocyte and its state of activation, the size of the cryptococcal capsule, and the availability of opsonins.