*Purpose: Our goal is to define the mechanism by which circulating exosomes with cardiac self-antigens (SAgs), Myosin, Vimentin, and angiotensin Receptor 1 Protein (AGTR1) leads to rejection of cardiac allografts in miR155 knockout animals and compare it with C57BL/6 transplants. Since miR155 is a regulator of the immune system and can suppress synthesized proteins, we postulated that delayed rejection of cardiac allografts in miR155KO is due to requirement for additional immune stimulation by exosomes from the graft.

*Methods: Heterotopic cardiac allografts were performed in the abdomen between Balb/c (H2kd) to C57BL/6 (H2kb) and Balb/c mice to C57BL/6 miR155KO. Blood was collected at day 7 and day 15 to determine antibodies (Abs) to SAgs, and circulating exosomes were characterized for SAgs. Exosomes were isolated using Total Exosome kit (Invitrogen) and size (<200nm) was measured using Nanosight. Immunohistochemical characterization (IHC) of the hearts were performed for histopathological and morphometric analysis of cells.

*Results: Cardiac allografts from Balb/c to C57BL/6 were rejected on day 7 and histopathology demonstrated damage to myocyte and cellular infiltration. These animals developed Abs to Vimentin (81±3.2 ng/ml) and Myosin (50.6 ±2.8 ng/ml) and exosomes with higher Myosin (14.0 folds), Vimentin (1.43 folds) and AGTR1 (1.67 folds). In contrast, miR155KO demonstrated functioning allografts on day 7. However, these animals developed Abs to Myosin (27.6±3.8 ng/ml) and Vimentin (62±5.8 ng/ml) and exosomes with myosin (3.2), Vimentin (0.67) and AGTR1 (2.0). IHC demonstrated increased CD3 and CD4 cells with deposition of Abs to AGTR1 (67.7%) and C4D. MiR155KO rejected the allografts on day 15 with characteristics of acute Ab mediated rejection. There were Abs to Myosin (16±2.2 ng/ml) and Vimentin (18±2.6 ng/ml) and exosomes with Vimentin: 0.58, Myosin: 2.6, AGTR1: 1.55 fold change respectively. IHC of the rejected hearts demonstrated CD3 (6.5%), CD4 (3.3%) cells and deposition of Abs to C4D (17.4%) and AGTR1 (60.7%).

*Conclusions: We conclude that the delayed rejection of cardiac allografts in miR155KO is due to the requirement of continued immune stimulation mediated by exosomes originating from the graft subsequent to development of Abs to SAgs. Further, IHC analysis of rejected allografts from miR15KO demonstrated a prominent role for Abs since increased deposition of C4D and AGTR1 was demonstrable.

« Back to 2020 American Transplant Congress