Introduction:

Kidneys have been the most frequently transplanted organs for many years. Success of renal transplantation is a function of several variables. However, the major determinant of the graft survival depends on the immune system’s ability to recognize foreign substances (antigens) expressed on the graft and to respond to them. Although, this defence mechanism is the base to survive in a hostile world of microorganisms, this

defence system becomes a major obstacle in renal and other organs transplantation. The likelihood of acceptance or rejection of the graft is closely related to the extent of genetic differences between the donor and the recipient of the graft. The major histocompatibility complex (MHC) genes encode proteins that are essential to immune recognition: MHC class I and II antigens. T lymphocytes interact through cell surface receptor known as T cell receptor (TCR) with MHC antigens found on the surface of