TLR4 and chronic obstructive pulmonary disease: Amongst TLRs, TLR-4 recognizes lipopolysaccharides of Gram (-) bacteria, while TLR-2 recognizes endogenous inflammatory mediators in addition to microbial products like lipotheicoic acid of Gram (+) bacteria [12], namely, the pathogens that play a crucial role, at least, in COPD phenotype (frequency and severity of exacerbation attacks) [13].