Delving deeper in the eye of the hurricane: Immunopathogenesis & molecular characterization of cytokine storm in COVID-19, association with disease severity & the therapeutic regimens

The COVID-19 pandemic elicited by SARS-CoV-2 has led to a world-wide crisis, affecting a substantial percentage of the entire global population, and has engendered profound morbidity and fatalities. SARS-CoV-2 mediates its entry into human respiratory epithelial cells via interaction between viral Spike protein (S) and ACE2 receptor and enacts the host cell tropism by numerous molecular factors and inflammatory signaling pathways. The complex molecular immunopathogenesis involves loss of regulatory control of the generation & release of proinflammatory cytokines at both local as well as systemic levels. Excessive secretion of pro-inflammatory cytokines and chemokines leads to the dysregulation of the innate immune system leading to the cytokine storm. Owing to the enormous release of inflammatory factors and active mediators, cytokine storm induces severe damage to secondary tissues, leading to Acute Respiratory Distress Syndrome (ARDS) or multiple-organ failure, which evokes aggravation of the disease and eventually death. Comparisons amid COVID-19 cytokine storm and several other types of cytokine storm associated diseases, gives proper insights about the etiology of cytokine storm in COVID-19. Various genetic and physiological factors contribute to severe disease progression and aggravation of the disease. In that view, several immunoregulatory therapies have been tailored to curb the cytokine storm, which might be crucial in improving the success rates of various treatment strategies as well as in lowering the mortality rate in COVID-19 patients. This review elucidates the hallmarks of COVID-19 cytokine storm, immunopathogenesis, disease progression, biomarkers, and therapeutic interventions.