Changes in the pulmonary surfactant in patients with mild COVID-19

Proteomic and lipid changes in the surfactant have been seen in severe COVID-19, but data on mild COVID-19 is scarce. We aimed to study if the protein and phospholipid profiles in the small airways alter in patients with an ongoing mild SARS-CoV-2 infection and at follow-up. 29 cases with mild COVID-19 (C19) and 17 healthy controls (HC) were examined at baseline. 22 cases were re-examined at follow-up after recovery from C19. Airwave oscillometry was performed and the biological material from small airways was collected with the PExA method in the form of exhaled particles. The SOMAscan proteomics platform was used for the analysis of proteins and LC-MSMS for lipids. Cases at baseline had increased R5 (p=0.039) and AX z-score (p=0.003) as compared to HC. Totally, 95 lipid species belonging to 8 classes were identified as well as 46 proteins. Among subjects with an ongoing infection, 10 proteins, among them several acute phase proteins (CFI, CFB, HPX, TF), positively correlated with R5-20 z-score (R=0.43-0.63, p<0.05). 13 lipid species were differentially abundant between cases at baseline and controls and 24 between cases at follow-up and controls (Fig. 1). The protein profiles did not differ between the cases and controls at either visit. The observed alterations in the phospholipids and acute phase proteins in the small airway lining fluid in mild COVID-19 patients indicate that surfactant homeostasis is affected already in a mild infection.