CHLOROQUINE INDUCES HUMAN MACROPHAGE KILLING OF HISTOPLASMA-CAPSULATUM BY LIMITING THE AVAILABILITY OF INTRACELLULAR IRON AND IS THERAPEUTIC IN A MURINE MODEL OF HISTOPLASMOSIS

We investigated the role of intracellular iron on the capacity of Hist oplasma capsulatum (Hc) yeasts to multiply within human macrophages (M phi). Coculture of Hc-infected M phi with the iron chelator deferoxam ine suppressed the growth of yeasts in a concentration-dependent manne r. The effect of deferoxamine was reversed by iron-saturated transferr in (holotransferrin) but not by iron-free transferrin (apotransferrin) . Chloroquine, which prevents release of iron from transferrin by rais ing endocytic and lysosomal pH, induced human M phi to kill Hc. The ef fect of chloroquine was reversed by iron nitriloacetate, an iron compo und that is soluble at neutral to alkaline pH, but not by holotransfer rin, which releases iron only in an acidic environment. Chloroquine (4 0-120 mg/kg) given intraperitoneally for 6 d to Hc-infected C57BL/6 mi ce significantly reduced the growth of Hc in a dose-dependent manner. At 120 mg/kg there was a 17- and 15-fold reduction (P < 0.01) in CFU i n spleens and livers, respectively. The therapeutic effect of chloroqu ine also correlated with the length of treatment. As little as 2 d of chloroquine therapy (120 mg/kg), when started at day 5 after infection , reduced CFU in tbe spleen by 50%. Treatment with chloroquine for 10 d after a lethal inoculum of Hc protected six of nine mice; all contro l mice were dead by day 11 (P = 0.009). This study demonstrates that: (a) iron is of critical importance to the survival and multiplication of Hc yeasts in human M phi; (b) in vitro, chloroquine induces M phi k illing of Hc yeasts by restricting the availability of intracellular i ron; and (c) in vivo, chloroquine significantly reduces the number of organisms in the spleens and livers of Hc-infected mice and can protec t mice from a lethal inoculum of Hc yeasts. Thus, chloroquine may be e ffective in the treatment of active histoplasmosis and also may be use ful in preventing relapse of histoplasmosis in patients with acquired immunodeficiency syndromes.