Loss of regulation of T helper 17 cells: a definitive factor for critical cases of coronavirus disease 2019

One of the greatest challenges in the study of coronavirus disease 2019 (COVID-19) has been to establish the determining factors in the severity of the disease. Through extensive research efforts, a crucial factor responsible for disease control or exacerbation in COVID-19 has been identified—the regulation of the immune response. The abnormal release of interleukin-1 (IL-1), IL-6, and tumor necrosis factor-alpha (TNF-α) has been extensively studied in the context of the altered immune response observed in severe cases of COVID-19. However, recent attention has turned towards the excessive release of IL-17 and the increased presence of T helper 17 (Th17) cells, the main secretory cells of this cytokine. These factors have garnered interest due to their potential involvement in the cytokine storm observed in severe cases of COVID-19. In this review, it will be delved into the intricate mechanisms by which IL-6 contributes to the differentiation of Th17 cells, resulting in an increase in the population of Th17 cells. Moreover, it will be explored the proportional relationship between the increase of these lymphocytes and the release of IL-17 and other chemokines, which all together play a key role in promoting the chemotaxis and activation of neutrophils. Ultimately, this cascade of events culminates in the generation of tissue damage by neutrophils. Additionally, therapeutic options targeting these lymphocytes and cytokines are explored, providing insights into potential avenues for intervention.