Adverse effects of elastase on host defense mechanisms and inflammation. In the cystic fibrosis airway, the concentration of elastase exceeds the concentration of inhibitors of elastase by several hundred to several thousand fold. While the vast majority of elastase is produced by the neutrophil, a small but significant amount is derived from bacteria. In addition to causing structural damage directly, elastase stimulates the production of pro-inflammatory mediators such as IL-8, which further induces neutrophil influx. Elastase also impairs mucociliary clearance by direct effects on ciliary function and by stimulating increased mucus production. Elastase inhibits opsonophagocytosis by cleaving the Fc portion of immunoglobulin G and complement receptors on both the neutrophil (CR1) and P. aeruginosa (C3bi), resulting in an opsonin-receptor mismatch.