CD274 and chronic obstructive pulmonary disease: The ratio of OX40L to PD-L1 expression is a quantitative measure of imbalanced DC co-stimulation, which is associated with the severity of pulmonary emphysema in patients with COPD (54 patients, mean age 59 years, 33 males, FEV1% 38) (46), suggesting that an imbalance of DC co-stimulation might contribute to the pathogenesis of COPD.