Fig. 1

IL-6 involvement in COVID-19- key manifestations and hypothetical mechanisms. IL-6 binds to IL-6 receptor (IL-6R) and glycoprotein 130 (gp130) to form a hexametric complex which is associated with the classical and trans-signaling pathways. Pharmacological inhibitors of IL-6 signaling prevent IL-6 from binding to IL-6R by targeting either the cytokine itself or the receptor. IL-6 is well known to play various physiological roles in cells and organs. For example, in macrophage IL-6 induces foam cell formation [5] and in macrophage, B cell, T cell and neutrophil, IL-6 induces inflammatory cytokines [3, 4]. And IL-6 induces leucocyte migration from blood to organs [3, 6]. IL-6 controls the level of NT-ProBNP and troponin [7]. In lung, IL-6 induces procalcitonin [8]. In liver, acute phase proteins including IL-6, CRP, C3, SAA, hepcidin, and fibrinogen are upregulated by IL-6, and albumin is downregulated by IL-6 [3, 4]