Calprotectin and inflammation-associated serum biomarkers determine critical illness in COVID-19

Little is known on the key contributing factors towards progression into acute respiratory distress syndrome (ARDS) necessitating mechanical ventilation (MV) in COVID-19. We determined serum levels, within 24 hours of diagnosis, of alarmins, as well as pro- and anti-inflammatory molecules in asymptomatic, moderate, severe and intubated patients compared to non-infected comparators. Levels of the pro-inflammatory interleukin (IL)-8, IL-18, matrix metalloproteinase-9, platelet-derived growth factor (PDGF)-B and calprotectin (S100A8/A9) were specific drivers of ARDS. Levels of the anti-inflammatory IL-1ra and IL-33r were increased; IL-38 was increased only in asymptomatic patients, but significantly decreased in the more severe COVID-19 cases. Multivariate ordinal regression showed that pathways of IL-6, IL-33 and calprotectin gave significant probability for worse outcome. These results indicate a dysfunctional response to the presence of alarmins that may be used for prognosis and development of effective treatments.