Proteomic characteristics of bronchoalveolar lavage fluid in critical COVID‐19 patients

Up to 10–20% of patients with coronavirus disease 2019 (COVID‐19) develop a severe pulmonary disease due to immune dysfunction and cytokine dysregulation. However, the extracellular proteomic characteristics in respiratory tract of these critical COVID‐19 patients still remain to be investigated. In the present study, we performed a quantitative proteomic analysis of the bronchoalveolar lavage fluid (BALF) from patients with critical COVID‐19 and from non‐COVID‐19 controls. Our study identified 358 differentially expressed BALF proteins ( P < 0.05), among which 41 were significantly changed after using the Benjamini–Hochberg correction ( q < 0.05). The up‐regulated signaling was found to be mainly involved in inflammatory signaling and response to oxidative stress. A series of increased extracellular factors including Tenascin‐C (TNC), Mucin‐1 (KL‐6 or MUC1), Lipocalin‐2 (LCN2), periostin (POSTN), Chitinase 3‐like 1 (CHI3L1 or YKL40), and S100A12, and the antigens including lymphocyte antigen 6D/E48 antigen (LY6D), CD9 antigen, CD177 antigen, and prostate stem cell antigen (PSCA) were identified, among which the proinflammatory factors TNC and KL‐6 were further validated in serum of another thirty‐nine COVID‐19 patients and healthy controls, showing high potentials of being biomarkers or therapeutic candidates for COVID‐19. This BALF proteome associated with COVID‐19 would also be a valuable resource for researches on anti‐inflammatory medication and understanding the molecular mechanisms of host response. Database Proteomic raw data are available in ProteomeXchange ( http://proteomecentral.proteomexchange.org ) under the accession number PXD022085, and in iProX ( www.iprox.org ) under the accession number IPX0002429000.