TIMP4 and chronic obstructive pulmonary disease: Notable other nominally significant or directionally inconsistent proteins in the findings are matrix metalloproteinase 8 (MMP-8), one of the proteases observationally associated with lung function and implicated in the pathogenesis of COPD [52, 53], TIMP4, an inhibitor of matrix metalloproteinases that has been shown to be upregulated in COPD patients [54] and CD14, levels of which have been shown to be elevated in lungs of smokers [55].