MUC5AC and respiratory system disorder: Goblet cell hyperplasia is another process associated with respiratory disease pathologies, and has recently been modelled in vitro during sub-cytotoxic repeated exposures to diluted combustible cigarette smoke (but was not induced by HTP aerosol exposure) (Haswell et al., 2021); Muc5AC is often used as a marker for mucin gene expression (Behrsing et al., 2016; Bedford et al., 2022).