The role of dendritic cells and T cell activation in allograft rejection

The lineage of dendritic leukocytes (DL) comprises cells that are widely distributed throughout lymphoid and non-lymphoid tissues, and which are phenotypically and functionally heterogeneous. These cells play a central role in the initiation of immune responses. Immature DL, which may be situated primarily in non-lymphoid tissues, are responsible for uptake and processing of native antigens, after which they migrate via blood and/or lymph into secondary lymphoid tissue, and develop into mature dendritic cells (DC). These cells can present foreign peptide-MHC complexes to resting T cells and deliver signals for T cell activation, thereby initiating the response. There is good evidence that DL can migrate from transplanted tissues into the recipient's lymphoid organs and initiate allograft rejection. Interruption of this process, by depleting DL before transplantation or by inhibiting their function, may contribute to the prevention of rejection in clinical transplantation.