Dendritic cells in immune responses against hepatitis C virus

摘要

Dendritic cells (DC) are unarguably the most potent professional antigen-presenting cells in vivo that play pivotal roles in the enhancement or regulation of immune reactions. They are continuously produced from haematopoietic stem cells in the bone marrow and are widely distributed, as immature DC, into both lymphoid and non-lymphoid tissues. Immature DC, including epidermal Langerhans cells and interstitial DC within non-lymphoid tissues, continuously sample selfantigens to maintain T cell self-tolerance. Immature DC also take up foreign antigens. When triggered by pathogens, immature DC mature to immunogenic DC to initiate primary T-cell-mediated immune responses. Some studies suggest that DC have the capacity to induce different types of T-cell-mediated immune responses, depending on their lineage, maturation stage and activation signals. In this sense the existence of functionally and ontogeneti-cally distinct DC subsets has been reported; i.e. myeloid DC and lymphoid DC. Myeloid DC produce IL-12 by inflammatory stimuli, while precursors of lymphoid DC release considerable amounts of interferon-alpha upon virus infection. Due to these properties, myeloid DC are potent in polarizing helper T cells to Thl type, while lymphoid DC are able to induce Th2 skewness. Thus, DC of myeloid or lymphoid lineage are often referred to as DC1 and DC2, respectively. In the steady state of healthy individuals the frequency of these DC subsets is extremely low, i.e. less than 1% of peripheral blood mononuclear cells (PBMC). However, the alterations in number and function of these DC have been reported in some virus infections and autoimmune disorders, suggesting their principal involvement in the pathogenesis or the outcomes of the diseases.