Single-cell transcriptome analysis reveals the heterogeneity of immune cells in peripheral blood of patients with mild and severe tuberculosis

<bold>Background:</bold> Tuberculosis is a serious global health burden. Several circulating cell subsets in the peripheral blood are known to modulate the host immune response to Mycobacterium tuberculosis (Mtb) infection. Tthe characteristics and functions of these subsets at different stages of tuberculosis infection have not been well elucidated. <bold>Methods:</bold> Peripheral blood immune cells (PBICs) from healthy controls (HC), individuals with mild tuberculosis (MTB), and individuals with severe tuberculosis (STB) were subjected to single-cell RNA sequencing (scRNA-seq). The metadata of cells was analyzed using the Seurat package. Pseudotime trajectory analysis was performed using the R package Monocle 3. Cell communication analysis was performed using the CellChat. <bold>Results:</bold> Cluster analysis based on differential gene expression revealed markers for all major cell types and delineated five major PBIC populations: neutrophil, T cell, monocytes, NK cells, and B cells. Further analysis showed that PBICs were highly heterogeneous, with significant differences in the same cell subset among the three groups. Cellular communication analysis revealed that CD8 T cells exhibited the highest incoming interaction strength in STB patients. The increased CD8 T cell incoming interactions are associated with the MHC-I and LCK pathways, with HLA-(A-E)-CD8A, HLA-(A-E)-CD8B, and LCK-(CD8A+CD8B) being ligand-receptor pairs. <bold>Conclusions:</bold> PBICs derived from HC, MTB patients and STB patients were highly heterogeneous, with significant differences in the same cell subset.