Characterization of Transfusion- Elicited Acute Antibody-Mediated Rejection in a Rat Model of Kidney Transplantation

Animal models of antibody-mediated rejection (ABMR) may provide important evidence supporting proof of concept. We elicited donor-specific antibodies (DSA) by transfusion of donor blood (Brown Norway RT1(n)) into a complete mismatch recipient (Lewis RT1(l)) 3 weeks prior to kidney transplantation. Sensitized recipients had increased anti-donor splenocyte IgG1, IgG2b and IgG2c DSA 1 week after transplantation. Histopathology was consistent with ABMR characterized by diffuse peritubular capillary C4d and moderate microvascular inflammation with peritubular capillaritis+glomerulitis>2. Immunofluorescence studies of kidney allograft tissue demonstrated a greater CD68/CD3 ratio in sensitized animals, primarily of the M1 (pro-inflammatory) phenotype, consistent with cytokine gene analyses that demonstrated a predominant T helper (T-H)1 (interferon-, IL-2) profile. Immunoblot analyses confirmed the activation of the M1 macrophage phenotype as interferon regulatory factor 5, inducible nitric oxide synthase and phagocytic NADPH oxidase 2 were significantly up-regulated. Clinical biopsy samples in sensitized patients with acute ABMR confirmed the dominance of M1 macrophage phenotype in humans. Despite the absence of tubulitis, we were unable to exclude the effects of T cell-mediated rejection. These studies suggest that M1 macrophages and T(H)1 cytokines play an important role in the pathogenesis of acute mixed rejection in sensitized allograft recipients. In this study, the investigators demonstrate that M1 macrophages and TH1 cytokines play an important role in the pathogenesis of acute mixed rejection in rat kidney transplant recipients sensitized by donor-specific blood transfusion.