SPP1 and chronic obstructive pulmonary disease: Although the majority of ligand-receptor (L-R) pairs mediating cell-cell interactions were shared between COPD and HS, distinct L-R pairs were also identified in each group, such as SPP1-CD44, SPP1-(ITGA5+ITGB1), and SPP1-(ITGA4+ITGB1) in COPD while LTA-TNFRSF1B, LTA-TNFRSF1A, LTA-TNFRSF14, and LTA-(LTB+LTBR) in HS (Supplementary Figure S7).