Fig. 5. Single-cell analysis of immune cells in COVID-19 patients. (A) The box plot describes the proportion of lymphocytes, neutrophil, and monocyte. The vertical axis indicates the values of laboratory indicators. The P -value was calculated using Wilcoxon’s rank-sum test and shown at the top of each panel. Boxplots represent the 25th and 75th percentiles, with midlines indicating the median values. ** represents P -value < 0.01. * represents P -value < 0.05. NS. representsP -value > 0.05. (B) The histogram shows the proportion of each cell type in healthy people (HC), mild patients, and severe patients. The vertical axis indicates the fraction of the cell type. Each color represents a cell type. (C) The t-distributed stochastic neighbor embedding (tSNE) plot of T cells for seventeen patients with COVID-19. (D) The tSNE plot of T cells colored by patient type. Red, green, and blue represent the HC, mild, and severe, respectively. (E) The tSNE plot of CD+8 T cells colored by cell-type-specific markers. The shade of the color represents the level of gene expression. (F) Violin plots of the inhibitory-receptors and cytokines’ gene expression. The vertical axis indicates the level of gene expression. (G) and (I) The tSNE plot of inhibitory-receptor coexpression patterns. Yellow represents the cells expressing two genes at the same time. (H) and (J) The bar plot shows the proportion of inhibitory-receptor coexpression patterns. The vertical axis indicates the rate of coexpression patterns.