We incubated COPD sputa from 4 subjects at week 5–6 after exacerbation, with and without A1-PI and inhibited the degradation of MUC5AC to just 6 % (SEM ± 9) and MUC5B to 11 % (SEM ± 3) of the native mucin concentration (Fig. 3b). Here, MUC5AC is linked to chronic obstructive pulmonary disease.