Reactive Oxygen Species Generated by NADPH Oxidase 2 Are Required For The LC‐3 Associated Phagocytosis (LAP) in Platelets Upon HIV‐1 Virions Endocytosis

Platelets play vital roles in maintaining hemostasis and immunological responses as well. Platelets have been shown to interact and endocytose several viruses such as influenza, hepatitis C virus (HCV) and human immune‐deficiency‐1 virus (HIV‐1). Most of these viremias are associated with thrombocytopenia and hyperactive platelets that could precipitate cardiovascular complications at advanced stages of the disease. Little is known about how platelets contribute to responses to viral infections. Using an HIV‐1 virion model, our lab has shown that human and mouse platelets endocytose HIV‐1 virions in a dynamin‐mediated process and traffic them through early (Rab4 + ) and late (Rab7 + ) endosomes finally to a LC3‐Ⅱ decorated compartment in a similar way to macrophages, the cell in which LC3‐Ⅱ Associated Phagocytosis (LAP) has been characterized. The trafficking through the endosomal compartments activates the endosomal toll‐like receptor‐7 (TLR‐7) in MyD88‐dependent manner, which activates downstream signaling cascades associated with platelet activation and secretion. In professional phagocytes, Reactive Oxygen Species (ROS) generated inside the phagosomes by NADPH Oxidase 2 (NOX2) are important for the recruitment of LC3‐Ⅱ to the phagosome. LC3‐II decoration is thought to improve fusion of the phagosome to the lysosomes for pathogen degradation. We are beginning to determine how much of this process is recapitulated in platelets. Platelets have all of the machinery and enzymes required for LAP formation and ROS production. We hypothesized that ROS generated by NOX2 inside of the phagosome are required for the recruitment of LC3‐Ⅱ to the phagosome upon HIV‐1 virions endocytosis . Our preliminary data show that NOX2 knock‐out platelets endocytose HIV‐1 virions, but they do not sequester the HIV‐1 virions in LC3‐Ⅱ decorated compartments. Our further studies focus on whether NOX2 also contributed to platelets activation following endocytosis of viral particles. These studies are meant to understand how platelets can respond during systemic viremia and thus direct the potential uses of antithrombotic drugs in such disease states.