ABSTRACT
This review assessed the complement system and its activation with respect to the pathological features of severe acute respiratory syndrome (SARS-CoV-2), human immunodeficiency virus (HIV) infection, and preeclampsia (PE). The complement system is the first defensive response of the host innate immune system to viral pathogens, including SARS-Cov-2. SARS-CoV-2 entry results in the release of proinflammatory cytokines and chemical mediators to create a "cytokine storm". Endothelial cell (EC) dysfunction and cell-mediated injury are also observed. These factors exacerbate inflammation. During HIV infection and PE, various complement components are elevated, causing a hyperinflammatory state. Furthermore, EC dysfunction and cell-mediated injury are also observed. The similarities in the pathological aspects of these three disorders may emanate from excessive complement activation. This review serves as a platform for further research on the complement system, coronavirus disease-2019, HIV, and PE.