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The expression of paired immunoglobin-like receptors A (PIR-A) and B (PIR-B) and their relationship with tolerogenic dendritic cells (T-DC) in mice were investigated. The mouse DCs line, DC2.4 cells were cultured with the recombinant murine interleukin-10 (IL-10) and recombinant human transforming growth factor β1 (TGF-β1) respectively to develop the T-DC and stimulated with lipopolysaccharide (LPS) for 48 h to induce the mature dendritic cells (LPS-DC). Special small interfering RNAs (siRNA) molecule for PIR-B was chemically synthesized and transfected into DC2.4 cells (Si-DC) by lip2000. The expression of PIRs on DC2.4 cells were detected by semi-quantitative reverse transcription polymerase chain reaction (RT-PCR), flow cytometry (FCM) and West blot. Realtime reverse transcriptase-polymerase chain reaction (Realtime-PCR) was applied for measurement of PIR-A and CD80, CD86, MHC-Ⅱ mRNA expression. The allogeneic stimulating capacity of DCs was measured by mixed lymphocyte reaction (MLR) using 3H-thymidine incorporation test. The concentration of IFN-γ in supatants of MLR from distinct groups was analyzed by ELISA. The results showed that PIR positive rate was (28.65±8.12)% examined by FCM on DC2.4 cells. PIR positive rate was increased dramatically to (54.21±6.34)%, (58.78±4.70)%,(48.24±6.75)% respectively for IL-10, TGF-β1 and LPS induction (P＜0.01), but there was no significantly different among the three groups (P＞0.01). The semi-quantitative RT-PCR and West blot revealed that IL-10 and TGF-β1 induced the higher PIR-B level and lower PIR-A level. On the contrary, the LPS down-regulated the PIR-B expression and up-regulated the PIR-A expression.Realtime PCR examination demonstrated that PIR-A and co-stimulating molecules such as CD80,CD86 and MHC-Ⅱ were increased significantly after stimulation with LPS. Compared with the DC2.4 cells and the LPS-DC, the T-DCs inhibited alloactived T cell proliferation and down-regulated the IFN-γ secretion in MLR supatant. Si-DC promoted the T cell proliferation (P＜0.01) and enhanced the IFN-γ secretion (P＜0.01). It was concluded that up-regulating the PIR-B and down-regulating the PIR-A expression were the general feature of phenotype and constructed the new targets for dendritic cells to acquire immune tolerance in mice. Overexpression of PIR-B can inhibit the up-regulation of the PIR-A, CD80, CD86 and MHC- Ⅱ expression, which might be the molecular mechanism for the T-DC.