OR24: MONOCYTE RECRUITMENT TO HUMAN LEUKOCYTE ANTIGEN CLASS I ANTIBODY-ACTIVATED ENDOTHELIAL CELLS IS DEPENDENT UPON MTOR

Abstract

Aim A hallmark of antibody (Ab)-mediated rejection is the presence of intravascular monocytes in the allograft. The purpose of this study was to determine the effects of rapamycin on monocyte recruitment and M1/M2 polarization in a clinically relevant in vivo model of antibody mediated-rejection (AMR). Methods Rag1 knock-out mice heterotopically transplanted with mismatched donor hearts were treated with rapamycin and received passive transfer of anti-donor antibodies (MHC I Ab). After 10 days, grafts were examined for histological features of AMR including microvascular inflammation and swelling and mononuclear cell infiltration by immunohistochemistry. Cross-sections of allograft tissue were stained for Mac-2 to assess myeloid infiltration, and for Arginase 1, a marker of polarized M2 macrophage subset. In vitro experiments were used to confirm the role of mTOR in monocyte recruitment to HLA-activated primary human aortic endothelial cells. Results The positive control group, which received anti-donor MHC antibodies, manifested with capillary injury, epicardial and pericardial damage, as well as infiltrating mononuclear cells into the graft vasculature and epicardial regions. Mice in the experimental group, which received daily intraperitoneal rapamycin treatment followed by biweekly anti-donor MHC antibodies, demonstrated reduced intra-graft cellularity and endothelial damage. HE a marker of inflammatory macrophages. Arginase 1 staining revealed M2 + macrophages were present in MHC Ab-treated allografts, and furthermore, the distribution of this subset partially overlapped with that of Mac-2. Though Mac-2 staining was found diffusely throughout the allograft, Arg1 positive macrophages localized primarily to the pericardium and fibrotic regions. Conclusion Antibody-mediated rejection drives the polarization of M2 macrophages, which can promote cell proliferation and tissue repair. mTOR blockade prevents monocyte recruitment to activated endothelium of cardiac allografts. S. Salehi: Grant/Research Support; Company/Organization; NIH.