Fig 1: Kinetic changes of respiratory leukocytes and their activities in respiratory specimens collected from COVID-19 patients(A) Cytological analysis of sputum (SPT) and bronchoalveolar lavage fluid (BALF) by H&E staining. The patient’s ID, collection day after symptom onset, and types of specimens (SPT and BALF) are presented. Orange arrows indicate PMNs (mostly neutrophils); red arrows indicate eosinophils; blue arrows indicate lymphocytes; and green arrow indicate macrophages. Scale bars, 20 µm.(B) Kinetic changes of the indicated leukocytes in respiratory specimens. Colored lines indicate smoothing splines. n = 45.(C) Kinetic changes in relative frequencies of the indicated leukocyte subsets in non-critical (blue, n = 20) and critical (red, n = 25) groups. Solid lines indicate non-linear regression with 95% confidential intervals. Dashed lines indicate data points from individual patients.(D–H) Kinetic changes of inflammatory markers derived from neutrophils (D), eosinophils (E), mast cells (F), macrophages (G), and cytotoxic T cells/NK cells (H) in respiratory specimens. Solid lines indicate non-linear regression with 95% confidential intervals. Violin plots show distribution of inflammatory marker levels in non-critical (NC) and critical (C) cases. ECP, eosinophilic cationic protein (n = 48 for non-critical and 36 for critical cases); EDN, eosinophil-derived neurotoxin (n = 43 for non-critical and 31 for critical cases); MCT, mast cell tryptase (n = 51 for non-critical and 38 for critical cases); LCN, lipocalin-2 (n = 24 for non-critical and 26 for critical cases); CALP, calprotectin (n = 11 for non-critical and 19 for critical cases); sCD163 and granzyme A (n = 18 for non-critical and 23 for critical cases). *p < 0.05, ***p < 0.001.