Single-Cell Transcriptomics Reveal Macrophage and T Cell Heterogeneity and Crosstalk from Granuloma Formation to Fibrosis in a Sarcoidosis Mouse Model

Sarcoidosis is a multisystem granulomatous disease that primarily affects the lungs. Although macrophages and T cells are implicated in the pathogenesis of sarcoidosis, their heterogeneity from granuloma formation to pulmonary fibrosis remains unclear. Using single-cell RNA sequencing (scRNA-seq), we characterized macrophages and T cells at different disease stages in lung tissues from Propionibacterium acnes (PA)-induced sarcoidosis-like model mice. The findings revealed that Lgals3 hi macrophages showed notable enrichment during both granuloma formation and fibrosis. Temporal transcriptional profiling of Lgals3 hi macrophages revealed a functional shift from pro-inflammatory signaling during the granulomatous stage to MHC-II antigen processing during fibrosis. Investigation of CD4 + T cell heterogeneity showed that CD4⁺ Th1 cells exhibited pro-inflammatory NF-κB profiles during granuloma formation, while adopting a migratory phenotype during fibrosis. Moreover, reduced Treg cell proliferative capacity was observed during fibrosis. Cellular communication analysis further revealed an upregulated MHC-II-mediated interaction between macrophages and CD4⁺ T cells both prior to PA re-exposure and during fibrosis. Together, our findings provide deeper insight into the cellular mechanisms underlying sarcoidosis progression, facilitating the identification of new therapeutic targets for the disease.