Toll-like Receptor 4 Attenuates A Murine Model Of Atopic Dermatitis Through Inhibition Of Langerin-positive DCs Migration

Background:Atopic dermatitis(AD)is a complex inflammatory skin disease that is induced by the interaction between genetic predisposition and environmental factors.Toll-like receptor(TLR)-4 on resident skin cells was involved in sensing pathogens and helping mount pathogen-specific innate and adaptive immune responses.The previous study has demonstrated that TLR4 was linked to AD severity in context of Escherichia coli exposure and vaccinia virus inoculation.However,the immunomodulatory role of TLR4 in DCs and T cell immune response during the pathogenesis of AD has not been fully understood.Part 1Objective:To investigate the regulatory role of TLR4 in hapten-induce AD mice model.Methods:Repeated epicutaneous application of a hapten,2,4-dinitrochlorobenzene(DNCB),was performed on the ear and dorsal skin of wild-type(WT)and TLR4 deficient(TLR4-/-)mice to induce AD-like symptoms.To investigate the immuoregulatory role of TLR4 in AD,we assayed the dermatitis severity,H&E staining,levels of serum IgE.IgGl and IgG2a,infiltration of mast cells and eosinohpils.Meanwhile,we also detected the inflammatory cytokines in lesions,Thl,Th2 cells in draining lymph nodes and migration of lagnerin-positive DCs between WT and TLR4-/-mice.Results:TLR4-/-mice exhibited more severe AD symptoms than WT mice after DNCB challenge.TLR4 deficiency promotes production of serum IgE and IgGl,and enhances the infiltration of mast cells and eosinophils to skin lesions in DNCB-treated mice(p<0.05).The DNCB-treated TLR4-/-mice also displayed higher expression levels of inflammatory cytokines and stronger Th2 response than WT counterparts.Furthermore,we demonstrated that the migration of langerin-positive DCs into draining lymph nodes was enhanced in TLR4-/-mice upon DNCB challenge(p<0.05).Conclusion:TLR4 deficiency aggravated the severity of DNCB-induced AD-like symptoms,accompanied by exacerbating clinical signs,inflammation infiltration,and Thl/Th2 imbalance.Moreover,TLR4 deficient mice presented increased percentage of langerin+ DCs in dLNs after repeated epicutaneous application of DNCB.Part 2Objective:To investigate the regulatory role of TLR4 in AD and illuminate the mechanism induced by repeated elicitation.Methods:To illuminate the mechanism that TLR4 attenuates a murine model of AD,we performed repeated epicutaneous application of DNCB on dorsal skin of WT and TLR4-/-mice.In some case,WT and TLR4-/-mice were injected subcutaneous with TNF-a receptor analog,Etanercept,in mice twice a week during the challenge process to inhibit TNF-a signaling in AD mice model.At the end of experiments,the migration of lagnerin-positive DCs,H&E staining,levels of serum IgE and Th2 related cytokines were examined.Results:the percentage of langerin+ DCs in dLNs was strongly decreased,and the dLNs collected from WT and TLR4-/-mice showed no significant difference in the frequency of langerin+ DCs after TNF-a inhibition.Blockade of TNF-a markedly reduction of the DNCB-induced AD symptoms in both WT and TLR4-/-mice,as evidence by skin pathology,Th2 related cytokines and serum IgE level(p<0.05).Conclusion:These results determined that TLR4 modulated production of TNF-a plays a crucial role in the pathogenesis of the hapten-induced AD model,suggesting that TLR4 may serve as a possible therapeutic target in AD.