Background: Antibody binding to its antigen can activate complement cascades leading to cell death. In addition, it can activate intracellular signals leading to rejection of transplanted organs. It has been demonstrated by us and others that immune responses to cardiac self-antigen (SAg) myosin can lead to rejection of cardiac allografts as well as syngeneic transplants. The mechanisms leading to rejection of syngeneic cardiac grafts following administration of antibodies to cardiac myosin remains unclear.

Method: Syngeneic cardiac transplants (HTx) were performed and rabbit anti-myosin (200[micro]g/ml), or control, was administered intravenously. Sera was collected following cessation of heart beat. To determine whether antibody binding to cardiac SAg myosin leads to circulating exosomes, sera was collected and exosomes were isolated by ultracentrifugation following anti-myosin administration. To determine the role of exosomes in inducing syngeneic cardiac graft rejection, following transplantation and administration of anti-myosin, an exosome blocking agent GW4869 (2.5ug/g) was administered intraperitoneally 1 hr prior to administration of anti-myosin. Sera was analyzed for development of antibodies to cardiac SAgs Myosin, Vimentin by ELISA. Induction of antigen specific T cell responses and the cytokines secreted were enumerated by ELISpot.

Results: Syngeneic HTx were rejected on day 7-10 following administration of Abs to cardiac myosin. Sera from the rejected animals developed not only antibodies to Myosin but also to Vimentin (25[micro]g/ml and 22 [micro]g/ml respectively) indicating spreading of immune responses. Administration of antibodies to myosin following transplantation also induced exosomes containing cardiac SAgs both myosin (1.5 fold) and vimentin (1.8 fold). Inhibition of exosome development with GW4869 decreased the release of exosomes (<20%), decreased CD4+ T-cells secreting IFN-γ (70spm) and IL-17(90spm) (p values<0.001and <0.01 respectively) with significant upregulation of IL-10 producing cells (1000spm). Development of antibodies to cardiac SAgs were also significantly reduced (p<0.05) following blocking of exosome development induced by antibodies to myosin.

Conclusion: We demonstrate that antibody binding to specific antigen (cardiac myosin) can result in induction of exosomes leading to spreading of immune responses to multiple cardiac self-antigens resulting in rejection of syngeneic cardiac grafts.

CITATION INFORMATION: Sharma M, Liu W, Gunasekaran M, Bansal S, Mohanakumar T. Binding of Antigens by Its Specific Antibodies Results in Exosome Formation Leading to Rejection of Syngeneic Murine Cardiac Grafts. Am J Transplant. 2017;17 (suppl 3).

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