Abstract: Objective:To investigate the expression of Toll like receptor 7(TLR7) in peripheral plasmacytoid dendritic cells(pDC) of patients with systemic lupus erythematosus(SLE),and its significance.Methods:Fifty two patients with SLE and 28 healthy persons were divided into the SLE group and control group,respectively.The proportion of TLR7+ pDC in peripheral blood were measured using flow cytometry.Results:The relative count of pDC in peripheral blood monouclear cells(PBMC) of SLE patients was significantly lower than that in control group(P<0.01),and there was no statistical significance in the relative count of myeloid dendritic cells(mDC) between SLE group and control group(P>0.05).The level of peripheral blood pDC in SLE patients was significantly lower than that in non-infected patients(P<0.01),and the level of peripheral blood mDC in patients with primary SLE was lower than that in recurrent patients(P<0.05),and there was a negative correlation between pDC level and CRP(P<0.05).The proportion of TLR7+ pDC in peripheral blood in SLE patients was significantly higher than that in control group(P<0.01).The proportion of TLR7+ pDC of SLE patients with hematological involvement was higher than that in patients without hematological involvement(P<0.05).There was no statistical significance in the proportion of TLR7+ pDC between anti dsDNA antibody,anti Sm antibody,anti SSA antibody,anti SSB antibody positive group and negative group(P>0.05).There was a positive correlation between the proportion of TLR7+ pDC and grade of proteinuria(P<0.01).Conclusions:The proportion of TLR7+ pDC in peripheral blood of patients with SLE significantly increases,and which is correlated with the disease activity.