MUC5AC drives COPD exacerbation severity through amplification of virus-induced airway inflammation

Aran Singanayagam; Joseph Footitt; Benjamin T Kasdorf; Matthias Marczynski; Michael T Cross; Lydia J Finney; Maria-Belen Trujillo Torralbo; Maria Calderazzo; Jie Zhu; Julia Aniscenko; Thomas B Clarke; Philip L Molyneaux; Nathan W Bartlett; Miriam F Moffatt; William O Cookson; Jadwiga Wedzicha; Christopher M Evans; Oliver Lieleg; Patrick Mallia; Sebastian L Johnston

Mucins were quantified in our study using ELISA-based assays in historically collected sputum samples specifically within a separated sputum plug aliquot, as this was the sample type available to us. Sputum plugs from severe asthmatics have previously been shown to contain more MUC5AC than MUC5B 40 and this constituent likely contains more surface goblet cell derived mucin which may contribute to the differences observed between induction of these two mucins in our studies. However, we also observed increased RVinduced MUC5AC but not MUC5B in an alternative sample type (BAL) from COPD subjects versus healthy subjects, supporting our findings in sputum. There is also evidence to suggest that proteases within sputum samples can interfere with immunodetection of mucins 14 . Some studies have attempted to address this by using treatment with protease inhibitors shortly after sputum collection 6, 41 . We have previously reported, using samples from the same study, that neutrophil elastase is increased in COPD subjects compared to healthy subjects following virus challenge 16 . Given that we observed greater induction of MUC5AC protein in COPD subjects compared to healthy subjects, despite increased levels of proteases, this suggests that the actual difference between these two groups could be even more substantial than observed in our study. Additionally, our finding that sputum MUC5AC but not MUC5B mRNA expression was increased during naturally-occurring exacerbation (mirroring what was observed at the protein level) provides an additional confirmatory approach that would not be subject to these potential confounders. Other studies have used alternative semi-quantitative antibody-independent techniques 7,14,42 but it is unclear whether these approaches would have sufficient sensitivity to detect subtle changes in mucin expression during infection. The primary aim of the human component of our study was to study how mucin levels change during virus-induced exacerbations and our study was unique in that we had sequential sampling from individual patients during exacerbation with consistent methods used to measure mucins in all subjects.