Immunological rejection is the major barrier to successful transplantation.The immune response to an allograft is an ongoing dialogue between the innate and adaptive immune system that will lead to the rejection of allograft.Activation of elements of the innate immune system,triggered as a consequence of tissue injury sustained during cell isolation or organ retrieval and ischemia reperfusion,will initiate and amplify the adaptive response.Identifying the molecular pathways that trigger tissue injury,signal transduction and rejection facilitates the identification of targets for the development of immunosuppressants.