In vivo killing of intracellular visceral Leishmani donovani by a macrophage-targeted hydrogen peroxide-generating system
In previous studies, we demonstrated that the macrophage's capacity to kill the intracellular amastigote form of Leishmania donovani, the etiologic agent of visceral leishmaniasis, is largely mediated by an oxygen-dependent mechanism. In order to kill amastigotes, it appears that activated macrophages must be able to respond to L. donovani ingestion with a respiratory burst and, in addition, generate high levels of toxic oxygen intermediates. Although macrophages secrete a variety of reactive oxidative products we found that H2O2 alone appears to be both necessary and sufficient to achieve leishmanicidal activity. In visceral leishmaniasis, the hepatic macrophage (the Kupffer cell [KC] lining the sinusoids) is a principal target for parasitization by L. donovani. In vitro, the resident murine KC generates little H2O2, fails to respond to amastigote investigation with respiratory burst activity, and supports L. donovani replication. The KC therefore appears to be an ideal target for which in vivo reconstitution with a H2O2-generating system might result in enhanced intracellular antileishmanial effects. In the present report, we have tested this hypothesis by delivering two forms of an enzymatic H2O2-generating system to infected KC - glucose oxidase (GO) bound to latex beads and GO enclosed within erythrocyte ghosts.