ABSTRACT Antibody-mediated mechanisms leading to acute and chronic renal allograft injury and loss remain poorly understood. Investigation into these mechanisms is hampered by the lack of appropriate animal models to study the development of allograft injury as the donor-specific antibody (DSA) response is initiated and progresses. We have developed a novel model of antibody-mediated rejection (ABMR) of kidney allografts in CCR5-/- recipients where DSA elicited in response to complete MHC-mismatched renal allografts are >50-fold higher than the titers elicited in wild-type recipients. The allografts are acutely rejected by the DSA in CCR5-/- recipients between days 17 and 22 with features that are virtually identical to those during acute ABMR of clinical kidney grafts, including identical histopathology and gene expression signatures indicating NK cell activation. We have recently demonstrated NK cell activation within the kidney allografts that is required for acute ABMR. In the absence of NK cell activation, however, the high DSA titers induced in CCR5-/- kidney allograft recipients are incapable of mediating acute ABMR but slowly induce development of tubular fibrosis and chronic glomerular injury that leads to eventual graft failure similar to that observed during late failure of clinical kidney transplants. Our preliminary results further indicate marked changes in the phenotype and functional transcriptome of graft infiltrating monocytes and macrophages during chronic vs. acute ABMR. Development of the chronic ABMR is also accompanied by the appearance of antibodies to several autoantigens that is not observed during acute AMR. These results suggest the generation of altered myeloid cells and autoantibodies as key mechanisms underlying the development of this chronic pathology and have led us to hypothesize that DSA binding to kidney allograft endothelium in the absence of NK cell activation stimulates production of myeloid cell recruitment and differentiation factors that skew their function to promote autoantibody production and development of chronic antibody-mediated graft injury. This hypothesis will be tested in three specific aims. In Specific Aim 1 we will test mechanisms of DSA-induced kidney allograft endothelial production of factors directing myeloid cell recruitment and function during development of chronic ABMR. In Specific Aim 2 we will test the role and functions of graft infiltrating myeloid cells that promote development of antibody-mediated allograft injury. In Specific Aim 3 we will test the production and role of auto-antibodies in the development of chronic ABMR. The proposed experiments will utilize novel and clinically relevant models of kidney allograft chronic ABMR to directly identify the inflammatory components and their mechanisms mediating chronic injury of the kidney grafts late after transplant. We anticipate that our studies will continue to reveal novel mechanisms critical to the development of kidney gra...