TNFSF4 and chronic obstructive pulmonary disease: The expression of OX40L on mDCs, the expression of PD-L1 on pDCs and the OX40L/PD-L1 ratio did not significantly differ between patients with spirometric GOLD stages II (n = 14), III (n = 26) and IV (n = 14) (Figure 6A-C) and between current smokers (n = 12) and former smokers with COPD (n = 42)(Figure 6D-F), although the highest median OX40L/PD-L1 ratios were found in the subgroup of current smokers with COPD and in the subgroup of patients with spirometric GOLD stage IV (Figure 6C, F).