Dendritic cells (DCs), the most potent professional antigen processing cells (APC) in vivo, play a crucial role in human immune system. DCs activate host immune response not only by their capturing and processing antigens to MHC-I and II molecules on the cellular surface, but also by their enhancing or regulating naive T cells and priming a primary immune response. The defects of DCs function in HBV-transgenic mice and HCV-infected patients were previously reported, but little is known in HBV-infected patients. In order to get more insights into the effects of DCs against persistent HBV infection in patients, this study addresses following three aspects: (1) To incubate and induce DCs subset populations differentiated from peripheral blood monocytes of HBV-infected patients in vitro and then characterize their function. (2) To investigate the fresh professional interferon-producing cells (IPCs) in peripheral blood and evaluate their significance involved in pathogenesis of chronic HBV infection. (3) Finally, investigate both the human T lymphocyte proliferation capability and the suppression effects on HBeAg expression in incubated 2.2.15 cells induced by mature human DCs following pure HBsAg antigen stimulation in vitro.Firstly, the DCs were enriched from peripheral blood mononuclear cells (PBMC) in forty-five HBV-infected patients and successfully induced by incubation with interleukin-4 (IL-4) and granulocyte-macrophage colony-stimulating factor (GM-CSF) in RPMI-1640 medium containing 10% PCS. On the third day incubation, the adherent DC cells from PBMCs were found to proliferate and had a rapid increase of cell number over time. The adherent cells achieved maximum proliferation on 12th day incubation. Flt-3 ligand, a kind of cytokine, was observed to promote the cell proliferation and increase the cell yield compared to the group without Flt-3, which may be related to the high expression of Flt-3 receptors on CD14+ cells from peripheralblood. Interestingly, the proliferation rate and total cell yield of DCs significantly decreased in chronically HBV-infected patients than those in healthy volunteers under the same incubation condition, which suggests that there is a functional default of DCs in patients with chronic hepatitis B virus infection.The expressions of CD80CB7-1 )> CD86(B7-2)^ CD la and MHC-II (HLA-DR) on DCs surface were identified by using flow cytometric analyses (FACS). The results showed that the expression levels of CD80, CD86, CDla and HLA-DR (44.27?.76%, 44.12 + 8.16%, 25.32 + 7.46% and 46.25 + 8.96% for HBV-infected patients vs 87.62 + 9.67%, 84.38 + 9.72%, 89.56+8.96% and 92.47 + 9.34% for healthy volunteers, respectively) were much lower in patients than those in healthy volunteers, while similar results of CD40> CDllc> CD83 and CD 123 identified by using FACS were also found between both groups of HBV-infected patients and healthy volunteers. There was a significant statistical difference between the HBV-infected patients and healthy donors (PO.05). The data of mixed lymphocyte reaction (MLR) showed the DCs from patients had a decreased allo-stimulatory capacity to induce the proliferation of T lymphocytes compared with the DCs from healthy donors. Furthermore, the production of decreased-interleukine-12 (IL-12) and increased-nitrogen monoxide (NO) levels was determined in the supernatants of MLR and pure DCs incubation system. NO was considered to injure the normal hepatocytes in liver tissues by inhibiting several kinds of enzyme activities. Our results suggest that DCs from HBV-infected patients have not only an immature phenotype, but also an impaired function. It is probably considered that decreasing expression of co-stimulatory molecules, reducing production of IL-12 cytokine and the active replications of HBV viruses in patients may be associated with the defect of DCs functions, but the exact underlying reason was unclear.Second, IPCs is precursor DC type II cells (pDC2), a kind of DC subsets. The fresh IPCs were detected in the peripheral blood of both HBV-infe