Innate Immune Responses in Transplant Immunity

Purpose of Review Despite a significant decrease in the rate of acute rejection, long-term solid organ allotransplant success is limited by chronic rejection. Transplant research has historically focused on adaptive immune responses. However, there is a growing appreciation that the innate immune system is a potential contributor to short- and long-term graft injuries. We seek to provide an overview of the current literature on innate immunity in transplantation, discussing both innate naïve and memory immune responses, mechanisms by which innate cells recognize allogeneic signals, specific subsets of innate cells implicated in these responses, and soluble mediators that may aid in the graft inflammation. Recent Findings The mechanisms by which innate cells recognize allogeneic tissue are being uncovered, and prior exposure to allogeneic cells may impact the strength of that response, thereby giving the innate cells “memory” of the previously encountered alloantigens. The implicated and discussed ligands & receptors for the innate immune recognition include ischemia-reperfusion injury products & the DAMP receptors, class I MHC & PIRA, CD47 & SIRPα. Additionally, the roles of macrophages, NK cells, γδ T cells, and complement proteins are examined. Summary It is likely that innate immune cells and pathways contribute to significantly altering the longevity of transplanted allografts, therefore warrant future investigations. Innate immune cells and their respective molecular targets might represent new points of intervention.