Abstract The focus of the research in the Lamb lab is to determine mechanisms of the immunopathogenesis of malaria. The long-term goal of the proposed work is to determine the molecular mechanisms of vascular leak in malaria. It is estimated that annually more than ~250 million people develop malaria worldwide resulting in over 600,000 deaths[1]. Malaria-associated respiratory distress syndrome (MA-ARDS) and malaria-associated acute lung injury (MA-ALI) are features of adult malaria where infection is caused by the species Plasmodium knowlesi and Plasmodium vivax. Despite the poor prognosis of this syndrome in malaria, very little is understood about the molecular players that mediate pulmonary vascular leak in MA-ARDS / MA-ALI. As such it is difficult to design new adjunct therapeutic strategies for this condition. CD8 T cell responses against the Plasmodium parasites that cause malaria are responsible for the pathogenesis of infection and are required for pulmonary vascular leak. Here we investigate our fascinating finding that co-infection of influenza with P. berghei NK65e prevents MA-ARDS / MA-ALI in mice. The proposed work will capitalize on this finding to establish the mechanisms by which protection occurs. Our published and preliminary data leads us to test the working hypothesis of this study that influenza modifies pulmonary vascular endothelial cells (PMVECs) and induces arginase 1 (Arg1)-producing monocytes as key protective mechanisms against CD8-mediated MA- ARDS / MA-ALI. Staggering of influenza A/X31 co-infection reveals protection only occurs when X31 infects at the same time as P. berghei NK65e suggesting an innate immune mechanism at play. We show that influenza A/X31 recruits a large number of Arg1-producing monocytes which are capable of suppressing the proliferation of polyclonally stimulated CD8 T cells. The rationale for the proposed work is that CD8 T cell responses are central to pulmonary vascular leak associated with malaria, and a more comprehensive understanding of how influenza prevents this damaging response will provide key information for the rational design of novel interventions to reverse pulmonary vascular leak in MA-ARDS / MA-ALI. We plan to test our central hypothesis and thereby accomplish the objective of this application by pursuing the following two specific aims: Aim 1: Determine whether influenza co-infection can suppress the pathogenic response of Plasmodium-reactive CD8 T cells directly or indirectly. Aim 2: Test the hypothesis that influenza-induced Arg1+ monocytes protect NK65e-infected mice from vascular leak.

Project Narrative Pulmonary vascular leak is a hallmark of severe malaria in adults infected with Plasmodium knowlesi and Plasmodium vivax yet the mechanism underlying how this occurs is poorly understood. Using a mouse model of malaria-induced pulmonary vascular leak our goal in this proposal is to identify mechanisms by which pulmonary vascular leak can be prevented in Plasmodium infection that could be harnessed in novel therapeutic strategies. The positive impact of this contribution will be: firstly, with respect to human health, the first step in a continuum of research that is expected to lead to the development of a novel adjunct therapy for preventing or reversing pulmonary vascular leak in Plasmodium infection; secondly, the proposed research is relevant to the part of the mission of the NIH that pertains to developing fundamental knowledge that will help to reduce the burdens of human disease and disability.