Mechanisms of Antibody Mediated Rejection in the Absence of Donor Specific Antibodies

Abstract

Purpose Antibody mediated rejection (AMR) is an increasingly studied cause of graft failure and cardiac allograft vasculopathy. The 1990 ISHLT Working Formulation first defined AMR as positive immunofluorescence staining of active complement in the graft endothelium and/or histologic evidence of vasculitis or severe edema in the absence of cellular infiltrates. Subsequent criteria included LV dysfunction plus donor specific antibodies (DSA); however the most recent criteria require pathological findings alone. This created a subset of patients with AMR without known mechanism. We hypothesized that non-HLA antibodies, i.e. other autoantibodies or natural antibodies (Nabs, poly-reactive antibodies against apoptotic cells), not identified by standard Luminex analysis, could be responsible for DSA-negative AMR. Methods We evaluated the pre-transplant sera of 74 heart transplant (HT) recipients between 2011-14 at our institution. Patients were categorized as having pathologic findings of AMR (pAMR1 or higher) in the presence of DSA, AMR in the absence of DSA or no AMR (controls). Serum obtained at the time of endomyocardial biopsy was analyzed for the presence of Nabs by MDA assay and apoptotic cell assay, as previously described by our lab. Furthermore, Immucor analyzed these serum samples for the presence of antibodies against a panel of 44 autoantigens. Results There was no difference in Nabs production, measured by MDA assay or reactivity to apoptotic cells, among the DSA-negative AMR, DSA-positive AMR and no AMR groups. The DSA-positive AMR group had more reactivity to autoantigens tested in the Immucor panel than the other groups. Each autoantigen had a significantly higher percentage of patients with reactivity in the DSA-positive AMR group compared to the DSA-negative AMR or no AMR groups. This difference was driven by statistically significant increases in reactivity against 16 of the 44 autoantigens tested. There was no difference between the DSA-negative AMR group and the no AMR group. Conclusion These data indicate that the autoantibodies tested for in this panel, as well as Nabs, are not associated with DSA-negative AMR. This suggests that autoantibodies may not be responsible for the effects manifested in patients experiencing this complication. Further research will be needed to investigate the mechanisms involved in DSA-negative AMR.