Regulation of Immunity by Dendritic Cells in the Setting of Liver Transplantation

The immune system is the defense mechanism of the human body for protection against infections and other unwanted biological invasions. There are two types of immune responses: the innate immune response and the adaptive immune response. Innate immune recognition relies on a limited number of germline-encoded innate immune receptors that recognize conserved products of microbial metabolism produced by pathogens, but not by the host. Recognition of these molecules allows the immune system to distinguish infectious nonself from noninfectious self (1). Antigen presenting cells (APC) form the bridge between the innate and the adaptive immune system, which has more variability and specificity. B en T cells are the mediators of the adaptive immune system. B-cells are the precursors of antibody secreting cells and can directly recognize antigens via their B-cell receptors, however T cells need the antigen to be processed and presented to them by an APC. The T-cell receptor (TCR) recognizes fragments of antigen in combination with molecules of the major histocompatibility complex (MHC). Two types of MHC molecules exist: MHC class I that is expressed by all nucleated cells in the human body and MHC class II that is expressed exclusively by APC, which present antigenic peptides to cytotoxic T cells and Thelper cells, respectively.

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