SPP1 and chronic obstructive pulmonary disease: This suppression in MDM from COPD patients was reversed when IL-13 was added (for OPN transcripts 5.0 ± 1.6 vs 3.0 ± 1.1, p < 0.001; for OPN levels 20.7 ± 1.6 ng/ml vs 8.3 ± 1.7 ng/ml, p < 0.001).