P038

Studying the infiltration kinetics and movement dynamics of macrophages in pancreatic islet grafts in vivo

Midhat H. Abdulreda, R. Damaris Molano, Judith Molina, Camillo Ricordi, Alejandro Caicedo, Antonello Pileggi, Per-Olof Berggren

Diabetes Research Institute, University of Miami, Miami, FL, United States

Macrophages are among the first and earliest immune cells to infiltrate pancreatic islets after transplantation. Macrophages participate in mediating an inflammatory milieu by locally producing cytokines and chemokines that result in T-lymphocyte recruitment to the target tissue; while syngeneic tissue is typically preserved, allogeneic tissue is ultimately rejected. In pancreatic islet transplantation, cytotoxic T-lymphocytes play a primary role in graft damage, however, oxidative stress mediated by the activation of infiltrating macrophages has been shown to play a part in allorejection. Here, we investigated the role of infiltrating macrophages and T-lymphocytes in islet allograft rejection by studying their infiltration kinetics and movement dynamics in the living organism. We performed noninvasive in vivo imaging of recipients’ GFP-expressing macrophages or T-lymphocytes as they infiltrated either syngeneic or allogeneic islets transplanted into the anterior chamber of the mouse eye. Intraocular transplantation enabled longitudinal studies in the same islet grafts revealing the kinetics of islet infiltration by immune cells and their movement dynamics within the islet grafts. While macrophage infiltration was observed in both syngeneic and allogeneic islet grafts, only allogeneic islets were rejected with progressive accumulation of T-lymphocytes. Longitudinal imaging revealed early and sustained infiltration of islet grafts by macrophages. While the number of infiltrating macrophages within syngeneic grafts remained constant throughout the follow up period (50 days), allogeneic islets showed noticeably higher macrophage infiltration, which significantly increased during the rejection phase. Also, the macrophage infiltration kinetics was slower than that of effector T-lymphocytes. These results suggest that macrophages may play different roles during the early post-transplant period and later during the rejection phase. Noninvasive imaging and the intraocular transplant model used in our studies are invaluable tools toward a better understanding of the role of macrophages in islet transplantation.