CD27 and chronic obstructive pulmonary disease: COPD B cells showed DEGs enriched in antigen presentation, BCR signaling, and inflammatory pathways (MAPK/NF‐κB/IL‐17/TLR; Figure S16B,C and Data S37), while CD27+ subsets were linked to neutrophil degranulation, cytokine signaling, and immune regulation (Figure S17A,B and Data S38).