Single-Cell RNA Sequencing Reveals the Immune Landscape of Granulomatous Mastitis

Granulomatous mastitis (GM) is a form of non-lactational breast inflammation that is closely associated with autoimmune processes, however its underlying pathogenesis remains elusive. In this study, we employed single-cell RNA sequencing (scRNA-seq) to conduct a comparative analysis of GM lesion tissues versus normal breast tissues, thereby unveiling the immune profile of GM tissues. Our investigation centered on T and NK cells, macrophages, epithelial cells, and endothelial cells. Notably, we observed a substantial infiltration of immune cells in GM tissues, accompanied by immune disorders, an elevation in Th1 cell counts, enrichment of the toll-like receptor (TLR) pathway, and upregulation of various factors including interferon-γ (IFN-γ), C-C motif chemokine ligand 3 (CCL3), CCL4, chemokine (C-X-C motif) ligand (CXCL) 13, CD69, signal transducer and activator of transcription 1 (STAT1), and heat shock protein family A member 1A (HSPA1A). Furthermore, the macrophage subpopulations in GM tissues exhibited a transition to a pro-inflammatory phenotype, enriched for pathways such as interferon-γ (IFN-γ), IFN-α, interleukin-6/janus kinase/signal transducer and activator of transcription 3 (IL-6/JAK/STAT3), and tumor necrosis factor-α/nuclear factor-κB (TNF-α/NF-κB). Mammary luminal cells demonstrated an impaired estrogenic profile yet displayed upregulation of prolactin downstream signaling pathways, namely the JAK/STAT and mitogen-activated protein kinase (MAPK) pathways. Additionally, vascular endothelial cells were found to recruit immune cells and exhibited a prominent angiogenic profile in GM tissues. Cellular interaction analysis unveiled an intricate network of interactions between mesenchymal and immune cells. This study provides a comprehensive immune landscape of granulomatous mastitis and offers some potential therapeutic targets for the disease.