The Role of Interleukin-6 in the Pathogenesis, Prognosis and Treatment of Severe COVID-19

A newly identified virus appeared in Wuhan, China, in December 2019, was named severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and caused the coronavirus disease 2019 (COVID-19). SARS-CoV-2 presents similarities with two previous coronavirus pandemics, MERS (Middle East Respiratory Syndrome) and SARSCoV, concerning phylogenetic origin, structural composition, and clinical symptoms, thus, leading to common pathogenic mechanisms. The purpose of this review is to declare the role of interleukin-6 (IL-6) in the pathogenesis, prognosis, and treatment of COVID-19 by comparing its effect on SARS-CoV and MERS cases. Increased levels of IL-6 comprise the key for the stimulation of cytokine storm and the progression of SARS, MERS, and COVID-19 cases. Especially, in COVID-19 patients, the overactivation of NF-k, which is caused by the binding of coronavirus spike protein S to alveolar epithelial cells, up-regulates IL-6 and promotes its systematic circulation, causing alveolar damage and extrapulmonary injury. Additionally, IL-6 can be used to evaluate respiratory failure and identify asymptomatic patients. Tocilizumab (TCZ), a monoclonal antibody which blocks IL-6 signaling, comprises a remedial option against COVID-19. TCZ improves oxygenation, reduces fever, and decreases levels of IL-6. IL-6 plays a major role in the pathogenesis of cytokine storm and the progression of COVID-19 and may be used as a therapeutic target against COVID-19. However, further research is needed concerning the relation of IL-6 in COVID-19 cases, and more clinical trials are required to declare TCZ as a treatment option.