Proposed schematic of the mechanism that TLR2-melatonin feedback loop regulates the activation of NLRP3 inflammasome in allergic airway inflammation. After TLR2 is activated by allergen, it subsequently induces NLRP3 inflammasome activation. Meanwhile, TLR2 inhibits the expression of melatonin synthetase ASMT, accordingly blocks 5-HT converting to melatonin, ultimately leading to the decreased level of melatonin. This inhibition of melatonin synthesis results in the loss of its inhibitory effect on the TLR2 signaling. The result of the cycle is the persistent of allergic airway inflammation.