TLR4 influences the expression of inflammatory cytokines and chemokines, such as TNF-α, IL-1, IL-6 and IL-8, and these cytokines and chemokines interact with each other, which in turn regulate the expression of TLR4 in the airway of patients with COPD [25–27]. Here, CXCL8 is linked to chronic obstructive pulmonary disease.