Quantification of lung IL-31 expression revealed that the percentage of IL-31-positive cells in patients with severe asthma (46.8% [34.3–61.5%]) was significantly greater than the percentages found in the patients with mild asthma (31.5% [18.6–42.8%]; p < 0.05) and the controls (10.4% [6.8–18.8%]; p < 0.01) (Fig. 6A–C,E). This evidence concerns the gene IL31 and asthma.