Furthermore, prostaglandin-endoperoxide synthase 2, a key enzyme in the production of pro-inflammatory prostaglandins [35], and IL-8, a major pro-inflammatory cytokine [36], were also down-regulated, suggesting that increased cytotoxic or pro-inflammatory actions are not the hallmarks of circulating eosinophils in asthma. This evidence concerns the gene PTGS2 and asthma.