Lung disease in relation to unique monocyte-macrophage subpopulations induced by combined inhalant endotoxin and collagen-induced arthritis

Lung disease is the most overrepresented cause of death in rheumatoid arthritis (RA). Animal studies have demonstrated potentiated autoimmunity, arthritis, and profibrotic/inflammatory lung disease with a combination of airborne exposures and collagen-induced arthritis (CIA), a model that recapitulates features of RA-associated interstitial lung disease (RA-ILD). As patients with RA-ILD demonstrate unique circulating monocyte subpopulations, this study aims to characterize lung infiltrating monocytes/macrophages in a mouse model of RA-ILD and determine whether reducing these cells mitigates the development of lung disease. Autoimmune-prone DBA/1J mice received intranasal inhalation of lipopolysaccharide (LPS) daily for up to 5 weeks and CIA induction. Experimental groups included Sham (saline injection/saline inhalation), CIA (CIA/saline), LPS (saline/LPS), and CIA+LPS (CIA/LPS). Lung disease was assessed by longitudinal imaging, lung function measurements, bronchoalveolar lavage fluid, lung tissues, and lung histopathology. Cell subpopulations were analyzed by single cell RNA-sequencing. Unsupervised clustering revealed 16 discrete clusters among the experimental groups with 2 robust clusters characterized as infiltrating inflammatory monocytes/macrophages for both CIA+LPS and CIA. The interaction of inhalation-induced airway inflammation and autoimmune arthritis results in lung disease associated with uniquely activated infiltrating inflammatory monocytes-macrophages that mediate adverse lung consequences. Whereas the induced monocyte/Mɸ immunophenotype is more aligned to CIA than endotoxin exposure, co-exposure modeling renders unique features that potentially inform the pathogenesis and treatment of RA-ILD.