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FUNCTIONAL CHANGES AND INCREASED APOPTOSIS OF DENDRITIC CELLS DURING CHRONIC HEPATITIS C INFECTION

L Zhao, L Tyrrell
Department of Medical Microbiology and Immunology, Faculty of Medicine and Dentistry, University of Alberta, Edmonton, Alberta

Patients with chronic hepatitis C virus (HCV) infection are reported to have impaired specific T cell responses. We hypothesized that dendritic cell (DC) function, number and intracellular signaling pathway are changed during chronic hepatitis C (CHC). Mixed lymphocyte reaction (MLR) was performed to reflect the overall capacity of DCs in stimulating lymphocyte proliferation, followed by detailed functional assays including endocytosis, expression of co-stimulatory molecules, cytokine secretion and expression of Fas ligand (FasL) of CHC patient DCs and healthy control DCs. The numbers of immature DCs circulating in peripheral blood were determined by four-color flow cytometry. The apoptosis rate of DCs was observed by terminal deoxynucleotidyl transferase biotin-dUTP nick end labeling (TUNEL). Furthermore, we studied signaling pathways in DCs, including Fas, TNF-related apoptosis-inducing ligand (TRAIL) and nuclear factor-kappa B (NF-kappaB). We report that CHC patient DCs are diminished in their capacity to stimulate lymphocyte responses, which can be attributed to their decreased expression of co-stimulatory molecules and increased expression of FasL, while their endocytosis and cytokine secretion functions are not changed. These results suggest that CHC patient DCs might switch their function from antigen presentation to killing of HCV-specific lymphocytes. In numeric assays, the number of immature DCs circulating in peripheral blood of CHC patients is not changed. However, DCs from CHC patients undergo apoptosis at a higher rate than DCs from healthy controls, which suggests that CHC patients might have fewer mature DCs in their hepatic lymph nodes. Finally, we found that NF-kappaB activity in CHC patient DCs is diminished, while Fas and TRAIL signals in CHC patient DCs are not changed. One or more of these changes could be responsible for the diminished capacity of DCs from CHC patients to stimulate lymphocyte responses. In conclusion, CHC patient DCs demonstrate functional changes and increased apoptosis, which might be due to diminished NF-kappaB activity in these cells.