In one study, the serum levels of calprotectin were elevated in patients with asthma and correlated with lung function, smoking, and blood neutrophil ratios in patients with asthma.[131] It was found that peripheral blood neutrophils from patients with asthma induced airway epithelial cells to produce S100A9, which further activated AECs through the ERK pathway, stimulated NET formation, and induced M1 macrophage polarization.[132]. This evidence concerns the gene S100A9 and asthma.