Mechanisms of cellular rejection
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Cellular mechanisms underlying the acute rejection are immune mechanisms that are not different as those involved against pathogens. The main difference relies on the nature of the antigen recognized which is, for rejection reactions, molecules (MHC molecules) that differ between members of the same species and act as transplantation barriers.
Four stages occurs successively in acute rejection:
- Allo-antigen recognition by T receptor
- T cell activation and clonal proliferation
- Graft infiltration
- Tubular and endothelial cell damage
Antigen Presenting Cells (APC) play a major role in the starting of cellular rejection mechanisms because APC are the cells that present antigen to T cells through the MHC molecules. A proportion of specific T cells (alloreactive T cells) may recognized the incompatible donor's MHC molecules carried on the APC. The recognition of incompatible MHC molecules is reffers to as allorecognition.
Once activated, alloreactive T cells migrate via blood to the graft and attack cells of the foreign tissue presenting the incompatible MHC molecules as they would do against infected cells.
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