Project Summary An ongoing outbreak of a novel coronavirus infection (COVID-19) has claimed hundreds of thousands of lives and disrupted social infrastructures around the world. Immunopathology from hyperactive host immune system contributes to the clinical severity of COVID-19. The proposed study will test the hypothesis that pathologic T cell and B cell interactions promote autoantibody production to mediate tissue damage in critically ill COVID-19 patients. In Aim 1, we will quantify the breadth and the specificity of antibody responses to self-antigens in COVID-19 patients. The goal of this aim is to measure the prevalence of autoantibodies and their functional significance in relationship to clinical disease severity. In Aim 2, we will define the structural-functional alterations to the immune subsets across multiple tissue compartments. We will apply high-dimensional imaging mass cytometry on autopsy samples from individuals who died from SARS-CoV-2 infection. The immune analyses will focus on B cell and T cell interactions, with additional markers for macrophages, neutrophils, and stromal compartments to comprehensively map the spatial organization of the immune microenvironments in LN, spleen, lung, heart, and the gastrointestinal tract. Antibodies targeting viral proteins and RNA intermediates will enable simultaneous visualization of infected cells, which will provide further insights into the relationship between viral infection and the immune response at the tissue-level. The proposed study will elucidate how autoantibodies may contribute to the immunopathology of COVID-19 and provide cellular unprecedented details on the architecture underlying COVID-related tissue damage. Insights into how SARS-CoV-2 causes host pathology could aid the identification of new targets for COVID-19 treatments to benefit veterans and the general population at large.