Pre-exposure Immunologic Health and Linkages to SARS-COV2 Serologic Responses, Endothelial Cell Resilience, and Cardiovascular Complications: Defining the mechanistic basis of high risk endotypes. Tim Chan David A. Zidar Abstract The objective of this proposal is to understand the immunologic foundations of heart disease which can occur as a result of COVID19. Cardiac impairment, when it develops is often fatal, and our hypothesis is that the maintenance of endothelial function is critical to surviving the protracted nature of COVID19 pneumonia, especially in those with reduced or delayed antibody responses. Our first aim will be to analyze those differences in immune function which pre-date infection but appear to impact the risk of fatal COVID. This will be done by enrolling those at high risk for developing COVID19 (frontline healthcare workers), and performing serially assessments of their immunologic function if they develop COVID. We will specifically investigate the mechanisms that link pre-infection inflammatory pathways to protective serologic responses and symptom severity and recovery. Our second aim will be to perform in vitro experiments to assess the requirements for endothelial cell dysfunction and infectivity. We will compare various inflammatory and cardiovascular stimuli which seem to play a role in promoting COVID19-related cardiovascular complications. Our third aim is to characterize immune cells, endothelial cells, and cardiomyocytes in heart tissue from those with COVID19-induced left ventricular dysfunction. Using single cell sequencing techniques, we will determine cellular and molecular signatures that characterize the microenvironment of the COVID19-affected heart, compared to appropriate controls. Our conceptual model is that pre-existing immune dysfunction 1) reduces the efficiency of neutralizing antibody responses, and 2) in conjunction with cardiovascular disease risk factors, induces endothelial downregulation/depletion of nodal regulators which protect against inflammatory insults. This renders endothelial cells unable to withstand COVID-specific stimuli. Once completed, this study will provide the necessary information to improve the identification of those at risk for COVID-related heart disease and develop rationale approaches to improve the improve survival in the setting of COVID.