Studies to date have looked at sputum, showing sputum contains higher levels of IL-6 and CXCL-8 at exacerbation [13], while alveolar macrophages taken from stable frequent exacerbator COPD released reduced CXCL-8 and TNFα in response to bacteria compared to infrequent exacerbators, suggesting an association between macrophage function and exacerbation frequency [14]. This evidence concerns the gene CXCL8 and chronic obstructive pulmonary disease.