The goal of this translational research is to optimize treatment in patients with visceral leishmaniasis (VL). In VL, parasites target, deactivate and replicate within tissue macrophages. Replication does not cease nor are parasites killed unless macrophage-activating host immune mechanisms supervene or chemotherapy is given. A logical route to the goal of optimizing treatment, then, is combining activated host mechanisms with chemotherapy. This project's objective is to advance the application of this strategy to amplify and accelerate the initial response to drug and produce long-lasting post-treatment effects to prevent relapse. VL is an ideal candidate for immunochemotherapy and its testing, since in this infection: (a) there is no vaccine, making drug therapy the mainstay of clinical management, (b) available chemotherapy is not optimal, (c) experimental understanding of mechanisms which activate or deactivate resistance is solid and ready to be built upon, (d) candidate host mechanisms can be identified in an in vivo model, and (e) experimental adjustment of these mechanisms is both feasible and therapeutic in established visceral infection. Nonetheless, gaps exist in our knowledege of specific host mechanisms to target in VL and in how to best translate immunochemotherapy. Results of the work proposed here in a model of Leishmania donovani (Ld) visceral infection will fill in these gaps, laying the groundwork for future interventions to employ with chemotherapy. To accomplish the Specific Aims, the Research Plan is practical -- testing responses in vivo, effects in established infection and hypotheses in relevant tissue foci where parasitized macrophages, influxing monocytes and T cells, and up- and downregulating immunoinflammatory mechanisms all intersect with drug. Aim 1: Determine how chemotherapy is converted to leishmanicidal. Aim 1 examines untested Th1-type mechanisms which likely govern responses to drug within the assembled tissue granuloma. Methods focus on mononuclear cell recruitment by potentially therapeutic chemokines, GM-CSF-induced blood monocyte influx and granuloma remodeling, and effects which may alter drug pharmacology in parasitized macrophages. Aim 2: Maximize chemotherapy's efficacy by simultaneously targeting more than one host mechanism. Aim 2's plan will amplify/accelerate responsiveness to drug therapy by rebalancing activating/deactivating mechanisms and boosting efficacy by targeting two immunologic pathways. Methods test Toll-like receptor responses, downstream MAPK signaling (p38, ERK1/2) and the IL-10-based deactivating cytokine network (IL-6, TGF-[unreadable], IL-27) induced by Ld.