Abstract Rationale The immune response in pulmonary fibrosis is spatially regulated and highly complex, driven by dynamic interactions between immune cells and stromal cells within the fibrotic microenvironment. Prior studies have shown that immunosuppressive therapies in idiopathic pulmonary fibrosis (IPF) are not only ineffective but may be harmful. In this study, we explored the immune landscape of IPF and identified spatially defined regions within fibrotic tissue. Methods Patients with idiopathic pulmonary fibrosis (IPF) and non-IPF controls were included in this study. Bronchoalveolar lavage fluid (BALF) samples were collected and cells subjected to scRNA-seq analyses. Spatial transcriptomics were performed on IPF lung tissues using the 10x Genomics Human Lung 5k panel. Spatial transcriptomics data was annotated using the Human Lung Cell Atlas resulting in the identification of 28 distinct cell clusters. Human CD8+ T cells were analyzed to evaluate their transcriptomic-effector states. Results In IPF and non-IPF BALF groups (n = 16; 8 per group) identified transcriptionally distinct cellular populations, encompassing T and NK cells, epithelial cells, stromal cells, mast cells, plasmacytoid and conventional dendritic cells, neutrophils, three subsets of alveolar macrophages, monocytes and monocyte-derived macrophages. Within the macrophage cluster, we identified an increase in CCL18+ macrophages in IPF patients. This finding was validated using the publicly available Rosas/Kaminski macrophage dataset (www.ipfcellatlas.com). Spatial transcriptomic analysis of IPF lung tissue revealed CCL18-enriched niches, in which CellChat identified a strong interaction between alveolar macrophages and CD8+ T cells among the top 20 predicted ligand–receptor pairs, suggesting immunoregulatory crosstalk. CCL18-enriched niches were closely associated with CD8+ T cells expressing exhaustion the markers, CTLA4, PDCD1, and LAG3, indicating that CCL18+ macrophages may promote CD8+T cell dysfunction through localized immunosuppressive interactions. Ex-vivo experiments with human CD8+T cells showed that CCL18 induced transcriptional responses indicative of impaired effector function and reduced cytotoxic killing of senescent cells. Conclusion Our findings support a role for CCL18+ macrophages in the induction of CD8+ T cell exhaustion within fibrotic niches in IPF lungs. These immunosuppressive niches may perpetuate fibrosis by impairing immunosurveillance and clearance of senescent cells. Our studies indicate that targeted therapies to re-invigorate CD8+ T cells may be effective in age-related pulmonary fibrosis. Funding Supported by NIH grants, R01 HL173154, R01 HL139617, R01 HL151702, and the U.S. Department of Veterans Affairs Merit Award I01BX003056. This abstract is funded by: Supported by NIH grants, R01 HL173154, R01 HL139617, R01 HL151702, and the U.S. Department of Veterans Affairs Merit Award I01BX003056.
Yadav et al. (Fri,) studied this question.