CXCL17 is a Prognostic Biomarker That Distinguishes Severe Pandemic InfluenzaA(H1N1) from COVID-19

Background: CXCL17 is chemotactic for myeloid cells, exhibits broad-spectrum bactericidal activity, and is expressed in mucosal tissues. This chemokine is constitutively expressed in the respiratory tract, suggesting a role for CXCL17 in lung defenses. However, little is known about the possible participation of CXCL17 during respiratory infections in humans. Here, we evaluated the role of CXCL17 as a biomarker in patients with severe pandemic influenza A(H1N1) and coronavirus disease 2019 (COVID-19). MethodsWe conducted a prospective cohort study in hospitalized patients with severe influenza A(H1N1) and COVID-19 admitted to two national reference centers in Mexico City. Peripheral blood samples were obtained on admission for determinations of the serum levels of CXCL17 by enzyme-linked immunosorbent assay (ELISA). The expression of CXCL17 in lung autopsy specimens from patients that succumbed to both diseases was assessed by immunohistochemistry (IHQ). Serum CXCL17 levels were compared between patients grouped according to their disease and clinical outcome. The diagnostic and predictive value of serum CXCL17 levels was evaluated using machine-learning algorithms and regression analyses. ResultsA total of 92 patients were enrolled in the study, from which 68 were infected with influenza and 24 had COVID-19. Their clinical characteristics were similar, although dyspnea, rhinorrhea, and sputum production were more common during influenza, whereas dry cough and vomit were more frequent among COVID-19 patients. Both diseases induced the local expression of CXCL17 in the lung. However, serum levels of CXCL17 were increased only in patients with influenza but not COVID-19. CXCL17 not only differentiates influenza from COVID-19 but serves as a prognostic biomarker associated with mortality and renal failure in influenza patients. Using cell culture assays, we also identified that human alveolar A549 cells and peripheral blood monocyte-derived macrophages produce CXCL17 after influenza A(H1N1) pdm09 virus infection. ConclusionsOur results suggest a possible role for CXCL17 in the pathogenesis of influenza A(H1N1), supporting the use of this molecule as a prognostic biomarker. Future studies on the role of CXCL17 in COVID-19 are warranted.