Male-Biased Macrophage Signaling and CD8 T Cell Dysfunction Drive Immunosuppression in Pulmonary Fibrosis

Introduction/Rationale: Idiopathic pulmonary fibrosis (IPF) is a progressive and fatal lung disease with marked sex-based disparities, as males show higher prevalence and worse outcomes than females. However, the cellular and immune mechanisms underlying these differences remain poorly understood.

Methods: To investigate sex-specific immune mechanisms in pulmonary fibrosis, we performed single-cell RNA sequencing (scRNA-seq) on lung tissues from male and female mice following bleomycin injury. Major immune and stromal cell populations were identified, and pathway enrichment analysis was used to define sex-biased signaling pathways.

Results: Autologous co-culture studies with precision-cut lung slices (PCLS) demonstrated greater collagen deposition in male PCLS, consistent with enhanced fibrotic activity. Similarly, in the bleomycin model, male mice developed more severe fibrosis and had poorer survival than females. scRNA-seq analysis revealed broad enrichment of pro-fibrotic and immunoregulatory pathways in male immune compartments. Macrophages in males showed activation of IL-8 signaling and PD-L1/PD-1 checkpoint pathways, indicative of immunosuppression and neutrophil recruitment. CD8 T cells displayed enrichment of apoptosis, TGF-β signaling, unfolded protein response, and negative regulation of type I interferon production. Moreover, male fibroblasts and epithelial cells expressed IL-4/IL-13, JAK/STAT3, and TGF-β pathways, programs likely to promote macrophage polarization and suppress effective T cell responses.

Conclusion: Male lungs exhibit upregulated immune checkpoint signaling, neutrophil-recruiting chemokines, and T cell exhaustion, reinforced by stromal-epithelial signaling. This immune dysregulation drives a pro-fibrotic, immunosuppressive environment and emphasizes sex-based disparities in IPF, pointing to therapeutic opportunities targeting male-biased immune pathways.