Expression of Surfactant protein D (SP-D) distinguishes severe pandemic influenza A(H1N1) from COVID-19
Abstract The differentiation of influenza and COVID-19 could constitute a diagnostic challenge during the ongoing winter due to their clinical similitude. Thus, novel biomarkers that enable distinguishing both diseases are required. Here, we evaluated whether the surfactant protein D (SP-D), a collectin produced at the alveolar epithelium with known immune properties, was useful to differentiate pandemic influenza A(H1N1) from COVID-19 in critically ill patients. Our results revealed high serum SP-D levels in severe pandemic influenza but not COVID-19 patients. This finding was validated in a separate cohort of mechanically ventilated COVID-19 patients who also showed low plasma SP-D levels. However, plasma SP-D levels did not distinguish seasonal influenza from COVID-19 in mild-to-moderate disease. Finally, we found that high serum SP-D levels were associated with mortality and renal failure among severe pandemic influenza cases. Thus, our studies have identified SP-D as a unique biomarker expressed during severe pandemic influenza but not COVID-19.
