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Zhitao Su, Lili Zhang, Stephen C Pflugfelder, De-quan Li; Toll-like Receptor Mediated Induction of TSLP and IL-33 by Murine Dendritic Cells in Response to Microbial Ligands. Invest. Ophthalmol. Vis. Sci. 2011;52(14):2908.
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Thymic stromal lymphopoietin (TSLP) and Interleukin (IL) 33 have been identified as two novel pro-allergic cytokines that initiate Th2-dominant allergic inflammation. This study was to explore the toll-like receptor (TLR) mediated induction of TSLP and IL-33 by murine dendritic cells (DCs) in response to microbial ligands.
Bone marrow cells were isolated from femur bone of BALB/c mouse, and cultured in RPMI1640 medium supplemented with 10% FBS, 20 ng/ml rmGM-CSF and 5 ng/ml rmIL-4 for 8-10 days. The induced immature DCs (iDCs) were treated with 9 microbial components (10µg/ml, each), ligands to TLRs 1-9, for 4-24 hours. The mRNA expression was determined by reverse transcription (RT) and real time PCR. The protein production was measured by ELISA or Western blot.
All TLRs 1-9 studied were found to be expressed by murine DCs as determined by RT and real-time PCR. Comparison of their mRNA levels showed that TLR2 and TLR7 were the most abundantly expressed, while TLR4 had the lowest expression. The induction of TSLP and IL-33 mRNA was found to reach peak levels at 4 hour fllowing TLR ligand stimulation. The mRNA expression of TSLP and IL-33 was markedly stimulated by multiple microbial components including Pam3csk4, poly I:C (dsRNA), LPS, flagellin and FSL-1, ligands for TLRs 1 and 3-6, respectively. Among them, LPS displayed the strongest stimulation of TSLP (13.6±7.8 fold) and IL-33 (12.7±5.1 fold). Interestingly, the expression of CD80 and CD86, markers for mature DCs, was also significantly induced by these TLR ligands with highest levels by LPS. This pattern of TSLP and IL-33 induction was confirmed at protein levels.
Our findings demonstrate that murine DCs express at least TLRs 1-9, and the pro-allergic cytokines TSLP and IL-33, which was induced through TLR-mediated pathway in response to microbial components, especially to ligands of TLRs 1 and 3-6. It suggests an important role of DCs in pathogenesis of allergic inflammation.
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