HLA-DRB1 and chronic obstructive pulmonary disease: Gene expression levels of the HLA-DRA (1.01 ± 0.43 versus 0.67 ± 0.23-fold change, adjusted p = 0.019) and HLA-DRB1 (1.42 ± 0.74 versus 0.81 ± 0.36-fold change, adjusted p = 0.011) genes were both elevated in the COPD-only group compared to the asthma-only group (see Supplementary Figure S4A,B).