[New views on immunopathology of viral hepatitis B and C]

The interaction of non-cythopatic, hepatotropic viruses of hepatitis B and C with the host's immune system plays a critical role in determining the viral clearance and it contributes to the liver damage. The initial line of defence is antigen non-specific and is mediated by natural killer cells and macrophages. Simultaneously, virus-specific immunity is induced by professional antigen presenting cells that process and present viral antigens to T and B lymphocytes in the regional lymph nodes. Thereafter, viral specific T helper cells are activated and these cells initiate the anti-viral immune responses of B and CTL lymphocytes. Early, multispecific T cell responses are associated with viral clearance, whereas the imbalance of viral specific Th1 and Th2 lymphocytes plays a crucial role in the viral persistence. The imbalance of viral specific Th1 and Th2 lymphocytes leads to inadequate activation of antigen specific CTL cells. After recognition of viral antigens, T helper lymphocytes are differentiated to Th1 and Th2 cells according to the type of secreted cytokines. Th1 cells produce cytokines: interleukin-2, IFN-gamma, TNF-alpha, which are responsible for effective activation of CTL cells. In contrast, interleukin-4, interleukin-5 and interleukin-10 are secreted by Th2 cells, which are involved in activation of B lymphocytes and in production of neutralizing antibodies. These finding suggests that the viral clearance is associated with the early development and adequate mounting of the anti-viral multispecific immune responses of T helper and cytotoxic T lymphocytes.