Protein analyzed by western blotting confirmed the results of mRNA and revealed that smokers with CRS and asthma had higher levels of MMP-1 (Fig. 3a,b, P = 0.032) and MMP-9 (Fig. 3a,c, P = 0.042) expression than those of non-smokers with CRS and asthma. This evidence concerns the gene MMP9 and asthma.