Finally, we found that treatment of melatonin resulted in dramatic increase in the protein expression of ASMT, marked elevation in the levels of 5-HT and melatonin, while did not affect the AANAT expression in comparing with vehicle-treated WT mice (Figures 6G–K). The protein expression of ASMT in lung tissues, the levels of 5-HT in BALF and melatonin in lung homogenate in melatonin-treated WT mice were comparable to that in vehicle-treated TLR2−/− mice post OVA challenge. However, TLR2−/− mice treated with luzindole showed notably reduced expressions of both AANAT and ASMT (Figures 6G–I), and lowered the level of melatonin in lung homogenate but not 5-HT in BALF in comparison with that of vehicle-treated TLR2−/− mice following OVA challenge (Figures 6J,K). Therefore, our study suggested that administration of melatonin further promoted endogenous melatonin biosynthesis, while treatment of luzindole significant inhibited endogenous melatonin synthesis in TLR2−/− mice.