Autoantibodies to components of apoptotic cells, such as anti-perlecan antibodies, contribute to rejection in organ transplant recipients. However, mechanisms of immunization to apoptotic components remain largely uncharacterized. We used large-scale proteomics, with validation by electron microscopy and biochemical methods, to compare the protein profiles of apoptotic bodies and apoptotic exosome-like vesicles, smaller extracellular vesicles released by endothelial cells downstream of caspase-3 activation. We identified apoptotic exosome-like vesicles as a central trigger for production of anti-perlecan antibodies and acceleration of rejection. Unlike apoptotic bodies, apoptotic exosome-like vesicles triggered the production of anti-perlecan antibodies in naïve mice and enhanced anti-perlecan antibody production and allograft inflammation in mice transplanted with an MHC (major histocompatibility complex)-incompatible aortic graft. The 20S proteasome core was active within apoptotic exosome-like vesicles and controlled their immunogenic activity. Finally, we showed that proteasome activity in circulating exosome-like vesicles increased after vascular injury in mice. These findings open new avenues for predicting and controlling maladaptive humoral responses to apoptotic cell components that enhance the risk of rejection after transplantation.

Acute vascular rejection (AVR) is characterized by

Commercially available human acellular dermal matrix (HADM), AlloDerm((R)), was implanted as an interpositional graft in the abdominal wall of adult vervet monkeys. Host response to implanted HADM was evaluated and compared with a human cellular dermal matrix (HCDM) and a primate acellular dermal matrix (PADM). Clinical acceptance of the acellular grafts (HADM and PADM) and graft remodeling were evidenced by fibroblast repopulation and neoangiogenesis. A mild inflammatory response marked predominantly by macrophages and T-cells was present in both HADM and PADM during the first month but was absent by 3 months. Similarly, antibody and complement deposition into the grafts as well as in the serum was evident only at the early time points. Interleukin-6 (IL-6) or IL-10 was induced in some acellular graft-implanted monkeys at the early time points, but tumor necrosis factor-alpha (TNF-alpha), interferon-gamma (IFN-gamma), or IL-2 was not detected over the study period. In contrast, significant inflammation was observed in HCDM-implanted animals, as evidenced by immune cell infiltration (p