**4.8 Role of innate immunity**

Although T cells play a critical role in acute rejection, the up-regulation of proinflammatory mediators in the allograft is now recognized to occur prior to T cell-mediated responses. This early inflammation following engraftment is due to the innate response to tissue injury that is independent of the adaptive immune system. Several recent studies have examined the role of Toll-like receptor (TLR) agonists and TLR signals in allorecognition and rejection.

The activation of innate mechanisms alone does not appear to be sufficient to lead to graft rejection itself. However, they are important for optimal adaptive immune responses to the graft and may play a major role in resistance to tolerance induction. The development of methods to blunt innate immune responses, which has potential implications for a wide variety of diseases, is likely to have a significant impact on transplantation as well.
