Abnormal expressed of PSMB9 and TAP2 gene are prominently associated with POCD, and both PSMB9 and TAP2 gene accompanied with other COPD-expressed genes such as PSMB8 and TAP1 involved in the antigen processing and presentation pathway, which might change phenotypes of alveolar epithelial type II cells in COPD lungs [81]. Here, PSMB8 is linked to chronic obstructive pulmonary disease.