A pro-inflammatory cytokine linked to host defense in lung disorders have been identified as a potential biomarker for severe COVID-19. The finding, which is reported in Frontiers of Immunology this week, may help in the diagnosis, monitoring, and treatment of the disease. Interleukin-26 (IL-26) is released by several immune and structural cells following stimulation of toll-like receptors and can directly inhibit viral replication and promote neutrophil chemotaxis. Although IL-26 is increasingly seen as a mediator of host defense in the lungs, its role in SARS-CoV-2 infection has not been established. A team led by scientists from the Karolinska Institutet examined the levels and activity of IL-26 in the plasma of patients with acute COVID-19 compared with healthy controls. They find that IL-26 is significantly increased in the blood of COVID-19 patients and that the concentration of IL-26 correlates with levels of several neutrophil-mobilizing cytokines. They also find that levels of IL-26 are correlated with two key biological markers of severe COVID-19. "Thus, IL-26 is involved in acute COVID-19, and it seems feasible that this intriguing kinocidin plays an important role in the hyperinflammation associated with acute COVID 19, a possibility that motivates further investigation into the clinical potential of IL-26 as a target for diagnosis, monitoring, and therapy in this deadly disease," the study's authors conclude.