Moreover, increased HLA-DQA1 and HLA-DR expressions were both associated with COPD frequent exacerbators, while serum soluble HLA-II molecule has been shown to be negatively correlated with values of forced expiratory volume in 1 s (FEV1) and FEV1/forced vital capacity (FVC) ratio in COPD patients. Here, HLA-DQA1 is linked to chronic obstructive pulmonary disease.