Effect of continuous administration of interferon-gamma in experimental visceral leishmaniasis.

In experimental visceral leishmaniasis, intermittently administered interferon-gamma (IFN-gamma) induces antileishmanial activity, which is primarily microbistatic. To determine if the efficacy of IFN-gamma immunotherapy could be enhanced by continuous delivery, Leishmania donovani-infected mice were treated using a subcutaneous osmotic pump. Once-daily intraperitoneal injections of 10(5) or 10(6) units of IFN-gamma inhibited the replication of L. donovani within liver macrophages but overall did not reduce liver parasite burdens. In contrast, a comparable dose of IFN-gamma (2.4 x 10(5) units/day) administered continuously induced an enhanced effect and reduced liver burdens by almost 50%. Although pump delivery did not similarly increase the efficacy of antimony chemotherapy in infected mice, continuous treatment with IFN-gamma plus antimony produced an additive antileishmanial effect. These results suggest that continuous infusions of macrophage-activating lymphokines such as IFN-gamma (used alone or in combination with chemotherapy) may be required to optimize in vivo antimicrobial effects.