The percentage of CD4+ T cells remained similar between patients and HDs (Figure 3D), whereas the CD294 MFI values on CD4+ T cells were higher in patient groups, particularly in stage 3–4 group (Figure 3D), suggesting the differentiation trajectory toward Th2 cells in the pathogenesis of COPD. This evidence concerns the gene PTGDR2 and chronic obstructive pulmonary disease.