Evolution of IL-6 as possible marker of viral control in Covid-19

Abstract

<b>Introduction:</b> Persistence of SARS-Cov-2 leads to immunosuppression and lack of viral control. Better understanding of the immune response throughout the course of evolution is important for a better patient management. <b>Methods:</b> Prospective observational longitudinal study of 91 hospitalised patients with different degrees of severity (moderate, severe, critical). In 72 we obtained ≥2 blood samples and classified them into viral phase (1-9 days after clinical onset), early inflammatory (10-16), and late inflammatory (&gt;17). We included clinical data, immune cell counts, proinflammatory cytokine levels, serum inflammatory markers, and tissue damage. <b>Results:</b> We observed higher serum IL-6 levels in the more severe groups, from the first sample. In inflammatory phases, we found a significant decrease in IL-6 and LDH in moderate, severe and survivors, and high persistence in critical and deceased patients. The biphasic behavior of IL-6 described, first neutrophil recruitment, epithelial and endothelial damage and then, after achieving viral control, CD4 differentiation, Th cells response and potentiation of Ac response, could explain these differences between those who do not achieve viral control (critical, deceased) and those who do. <b>Conclusions:</b> - IL-6 levels at 10-16 days may indicate whether or not viral control is achieved and whether there may be progression to critical stage/death. - The absence of IL-6 decline at 10-16 days was associated may be associated with poor prognosis and may guide the initiation of IL-6 blocking therapy.