This finding is in keeping with those of previous reports in which the investigators compared levels of MUC5AC and MUC5B in sputum obtained by means of nebulization with differing strengths of saline or that obtained by means of spontaneous expectoration19 MUC2 was not measured because quantitative immunoblotting and mass spectrometry analysis of sputum from healthy subjects and individuals with asthma, cystic fibrosis, or COPD showed little evidence for the presence of MUC2.39 Here, MUC5AC is linked to chronic obstructive pulmonary disease.