Mechanistic understanding of innate and adaptive immune responses in SARS-CoV-2 infection

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infections have triggered global pandemic that continue to impact adversely human health. New understanding has emerged about the innate and adaptive immune responses elicited in SARS-CoV-2 infection. The understanding of innate immune responses generated in hosts early in SARS-CoV-2 infection is vital for treatment efforts. Antiviral cytokines are released by innate immune cells in response to viral infections that play a pivotal role in limiting viral replication, pathology and generating optimal adaptive immune responses alongside the long-term memory responses against reinfections. One aspect of innate immune response generated against SARS-CoV-2 in vivo and which has received much attention has been high proinflammatory cytokine release in COVID-19 patients. Another vital discovery has been that the antiviral cytokine type I Interferon (IFN) family IFN-α mediates upregulation of angiotensin converting enzyme 2 (ACE2) membrane protein in airway epithelial cells. ACE2 is a receptor that SARS-CoV-2 binds to infect host cells. New understanding has emerged about the mechanism of SARS-CoV-2 induced exaggerated proinflammatory cytokine release as well as transcriptional regulation of ACE2. This review discusses various mechanisms underlying SARS-CoV-2 induced exaggerated proinflammatory cytokine response as well as transcriptional regulation of ACE2 receptor. We further elaborate on adaptive and memory responses generated against SARS-CoV-2.