TLR4 and chronic obstructive pulmonary disease: Studies have shown that the exposure to cigarette smoke (one of the major instigator of COPD) significantly correlate with the increased gene expression of both Toll-like receptors, TLR4 and TLR9 as well as cytokine production (Bezemer et al., 2012[2]; Nadigel et al., 2011[16]).