S100A9 and chronic obstructive pulmonary disease: Several studies have demonstrated altered levels of CHDP cathelicidin and calprotectin (a complex of subunits S100A8 and S100A9) in various chronic inflammatory diseases including rheumatoid arthritis (RA), chronic obstructive pulmonary disease (COPD), asthma, inflammatory bowel disease (IBD) and atherosclerosis (3–12).