COPD patients display pronounced changes of IL-33 and ST2 expression in alveolar capillary phenotypes

<bold>Background:</bold> IL-33 is highlighted as a potential drug target in COPD. Despite this, critical knowledge about which cell types are involved in IL-33 mediated immunity in the distal lung remains elusive. <bold>Aim:</bold> To reveal the cellular distribution and expression of IL-33 and membrane and soluble splice variants of its receptor, ST2 (mST2 and sST2 respectively), in the distal lung of COPD patients. <bold>Methods:</bold> Lungs from 15 COPD patients and 8 controls were subjected to cutting-edge combined multiplex in situ hybridization and immunohistochemistry (mISH-IHC) to yield spatially resolved single-cell expression data. <bold>Results:</bold> Single-cell data identified endothelial cells as a major source of IL-33 and ST2 in the distal lung. The mISH-IHC analysis revealed a patchy upregulation of IL-33 and ST2 across CD31+, PECAM1+ alveolar capillary populations in COPD lungs (IL33 p<0.0001; sST2 p=0.0003; mST2 p<0.0001). Using markers to resolve endothelial sub-populations, data showed that general alveolar capillaries (gCap) had high baseline expression of IL-33, which was upregulated in COPD (p=0.02). Aerocytes (aCap) showed an increase in IL-33 and mST2 expression respectively (p=0.009, p=0.01) in COPD compared to healthy aerocytes. Mast cells were the primary immune cells expressing both sST2 and mST2, with an upregulation in COPD lungs (p=0.03, p=0.02). <bold>Conclusions:</bold> The identified subtypes of alveolar endothelial cells seem to play distinct and significant roles in IL-33 mediated immunity, with apparent activation in COPD. By exposing the structural basis for IL-33 mediated inflammation in human lungs, our findings offer crucial insights for developing treatment strategies that target this pathway in COPD.