TLR4 and asthma: Some studies demonstrated beneficial effects of TLR4 agonists such as lipopolysaccharide (LPS) in asthma [41, 42], whereas others reported pivotal role of LPS-TLR4 signaling in asthma exacerbation, which paralleled clinical signs of microbial asthma exacerbation, including extended disease duration and worsen symptoms [43].