MMP9 and cystic fibrosis: These results, together with those previously obtained [26], indicate that the expression of MMP9 is related to the response of the PwCF to CFTR modulators, and that by elucidating the NF-kB signaling pathway, which is related to MMP9 expression, it may be possible to understand the molecular events underlying the variability in the clinical responses of PwCF to their CF therapies.