Identification of SPP1-positive macrophages by single-cell spatial analysis in human lung tissues with mycobacterial infection

Tuberculosis and non-tuberculous mycobacterial (NTM) diseases are infections caused by Mycobacterium tuberculosis and non-tuberculous mycobacteria such as Mycobacterium avium complex, leading to the formation of granulomatous lesions with caseous necrosis in the lungs. Although granulomatous tissues are infiltrated by numerous inflammatory cells, including macrophages, lymphocytes, and neutrophils, the mechanisms underlying granuloma formation by mycobacteria remain unclear. In this study, we performed single-cell spatial analysis on lung tissue samples from patients with tuberculosis and NTM diseases to investigate the infiltrating cell populations. We analyzed seven lung lesions and identified individual cell types infiltrating the granulomatous tissue. Based on gene expression profiles, at least four macrophage subtypes were identified. Notably, SPP1-positive macrophages predominantly infiltrated the granulomatous tissue. Langhans giant cells expressed SPP1, and many SPP1-positive macrophages without giant cell morphology were also present around the granuloma. RNA-seq analysis revealed elevated SPP1 expression in mycobacterium-infected tissues. The SPP1-CD44 signaling pathway was active in SPP1-positive macrophages and their neighboring cells in mycobacterium-infected tissues. SPP1-positive macrophages were also observed around granulomas in other granulomatous diseases, such as granulomatosis with polyangiitis and sarcoidosis. These findings suggest that SPP1-positive macrophages may play a key role in granuloma formation in granulomatous diseases, including mycobacterial infections.