Objective To investigate the effects of Dermatophagoides pteronyssinus ( Der p) on the expression of TLR4 and IL-4 in P815 mast cells and to further analyze the immunoregulatory effects of 1,25-(OH)2D3 on Der p treated P815 mast cells.Methods Different concentrations of Der p and 1,25-( OH) 2 D3 were used alone or in combination to stimulate P815 mast cells.The supernatants of the stimulated cell culture were analyzed by enzyme-linked immunosorbent assay ( ELISA) for the detection of IL-4.The stimulated cells were collected and analyzed by real-time PCR and Western blot assays for the detection of TLR4atmRNAandproteinlevels,respectively.Results (1)TLR4expressionwasdetectedinP815 cells.The expression of TLR4 was enhanced in P815 cells treated with various concentrations of Der p.A significant dose-dependent up-regulation of TLR4 was observed in P815 cells after incubation with Der p for 36 h.(2) Der p promoted the release of IL-4 in P815 cells (P<0.05).(3) No significant differences with the expression of TLR4 and IL-4 were observed among 1,25(OH)2D3 treatment groups as compared with the control group (P>0.05).(4) 10-8 mol/L of 1,25(OH)2D3 promoted the Der p-induced expression of TLR4 in P815 cells (P<0.01).However, 1,25(OH)2D3 inhibited the release of IL-4 in a dose-dependent manner(P<0.05orP<0.01).Conclusion (1)Derpcouldpromotetheinflammationandallergicreac-tion through up-regulating TLR4 and IL-4 in mast cells.(2) The possible mechanism for the inhibitory of 1, 25(OH)2D3 on Der p-induced immune responses was due to the suppression of Th2-type immune responses through inhibiting the synthesis and secretion of IL-4 in mast cells.