CXCL8 and chronic obstructive pulmonary disease: Both mRNA and soluble levels of TLR2 in patients with COPD were significantly associated with sputum levels of CXCL8 mRNA (r = 0.495, P < 0.001,  N = 41) and protein (r = 0.614, P < 0.001, N = 52), MMP-9 mRNA (r = 0.377, P = 0.0016, N = 41) and protein (r = 0.493, P < 0.001, N = 51), and NE mRNA (r = 0.518, P < 0.001, N = 39) and protein (r = 0.351,  P < 0.001,  N = 49).