Landscape of T Cells in Tuberculous Pleural Effusion

The distribution and the function of T lymphocyte subsets in pleural effusion (PE) and peripheral blood (PB) in tuberculous pleural effusion (TPE) patients remain unclear. In this study, we aimed to explore the expression patterns, regulatory mechanisms, and functions of T lymphocyte subsets in TPE patients, especially the distribution of T lymphocyte subsets at the single cell level. The CD3⁺ T cells were isolated from PE and PB of four TPE patients for single-cell RNA sequencing (scRNA-seq) to screen T cell subsets. T-SNE projection, Gene Set Variation Analysis (GSVA), and pseudotime analysis were performed to analyze the composition, molecular and functional properties, and developmental trajectories of T cell subsets. Finally, ELISA was carried out to identify the cytokines secreted by PE and PB. We found that CD4⁺CD8^- T lymphocytes (Th1, Th2, and FOXP3⁺ Treg cells) were preferentially enriched in PE. The proportion of exhausted CD4^-CD8⁺ cells in PE was higher than that in PB, while the proportion of initial and effector CD4^-CD8⁺ cells was quite the reverse. We also found a large number of unexpected double positive (DP) cells in PE and PB, among which the proportion of CD4⁺CD8⁺-C10-CCL3 cells was the most different between PE and PB. Meanwhile, CD4⁺CD8⁺-C10-CCL3 was the group with the largest number of interactions with other groups. CD4^-CD8^- cells were mainly found in PE and may be involved in the immunomodulatory effect of PE. Furthermore, the concentrations of cytokines secreted by Th1, Th2, and Treg in PE were higher than those in PB. Our study is helpful to understand the distribution pattern and dynamic changes of T cells in PE and PB of TPE patients and further understand that the functional status and regulation of T cells will be crucial for the successful development of TPE immunotherapy.