Chemokines and Chronic Heart Allograft Rejection

Abstract

Early work reported that targeting the CXCR3 and CCR5 could delay, but not prevent, acute allograft rejection (1–6). However, it is unclear how targeting single or multiple chemokine receptors could affect chronic rejection. In this study, we have examined the importance of chemokine receptors in acute and chronic rejection using CCR2, CXCR3, CCR5 knockout mice and CXCR3/CCR5 double knockout mice with heart allografts. Transplanted heart grafts were harvested at or near cessation of palpable contractility or at 60 days for chronic rejection, bisected to create a four-chamber section to visualize the aortic anastomosis, where chronic allograft vasculopathy is most readily identified. The median survival times for B6, CCR2−/−, CCR5−/−, CXCR3−/−, and CXCR3−/− × CCR5−/− recipients of heart allografts from complete major histocompatibility complex mismatch Balb/c donors were 8, 9, 11, 12, and 14 days, respectively. The pathology of acute rejections was similar in all mice with a mononuclear infiltrates and myocyte necrosis, diagnostic of acute cellular rejection (Fig. 1A, D, G, J, and M).FIGURE 1.: Histopathology of acute and chronic rejection. Acute rejection of Balb/c allografts showing mononuclear cell infiltrates with myocyte necrosis (A, D, G, J, and M). Recipients are B6 (A), CCR2−/− (D), CCR5−/− (G) CXCR3−/− (J), and CXCR3−/− × CCR5−/− DKO (M). Histopathology of active chronic rejection of BM12 allograft showing coronary and intraparenchymal arteries infiltrated by mononuclear cells with endothelialitis (B, E, H, K, and N). Recipients are B6 (B), CCR2−/− (E), CCR5−/− (H), CXCR3−/− (K), and CXCR3−/− × CCR5−/− DKO (N). Histopathology of active chronic rejection of BM12 allograft showing donor aortas at the anastomotic site infiltrated by mononuclear cells with endothelialitis (C, F, I, L, and O, and R). Recipients are B6 (C), CCR2−/− (F), CCR5−/− (I), CXCR3−/− (L), and CXCR3−/− × CCR5−/− DKO (O). Hematoxylin/eosin stained slides. Original magnification, 400×.Using a well-established model of chronic rejection (7–9), hearts from donor BM12 mice were transplanted into B6, CCR2−/−, CCR5−/−, CXCR3−/−, and CXCR3−/− × CCR5−/− recipients. In both control and the KO animals, coronary arteries and/or intramural arteries contained intimal and medial mononuclear cell infiltrates with endothelialitis (Fig. 1B, E, H, K, and N) with similar infiltrates in the donor aorta adjacent to the aortic anastomotic site (Fig. 1C, F, I, L, and O). Morphometric analysis failed to identify any quantitative differences among animal groups. In addition, smooth muscle cell loss was present in the donor aortas. These histological findings are diagnostic of an active phase of chronic allograft vasculopathy. Little parenchymal inflammation was present in all chronic rejection recipients. Syngeneic allografts showed no intimal hyperplasia or inflammation in the coronary arteries or at the anastomotic site (data not shown). In this study, there was modest prolongation of acute heart allograft survival in the mice deficient for certain chemokine receptors and there was no effect on chronic rejection. Chemokines control the inflammatory infiltrate so that a modest delay in the recruitment of cells, especially CD4 cells, could have a modest effect on acute cellular rejection and chronic allograft vasculopathy (10–14). Because there is redundancy in the chemokine and chemokine receptor network deleting or targeting a single chemokine or receptor has only marginal effects in acute cellular rejection (15, 16). Additional prolongation observed in the DKO mice suggests that targeting multiple chemokine receptors may further delay rejection. Potent costimulatory blockade or conventional immunosuppressive strategies, which dramatically reduces parenchymal inflammation, is also often unable to reduce chronic rejection (17–21). Likewise in this BM12 model of chronic rejection using B6 and selected chemokine receptor knockout recipients, there is relatively little parenchymal inflammation with ongoing active chronic vasculopathy. Parenchymal infiltration, therefore, is probably not the trigger for the development of chronic allograft vasculopathy, which may come about by an inflammatory pathway distinct from that which recruits parenchymal inflammation. R. Neal Smith Department of Pathology, Massachusetts General Hospital, Harvard Medical School, Boston, MA Takuya Ueno Transplantation Unit, Surgical Services, Massachusetts General Hospital, Transplantation Research Center, Brigham and Women’s Hospital, Harvard Medical School, Boston, MA Toshiro Ito Transplantation Unit, Surgical Services, Massachusetts General Hospital, Harvard Medical School, Boston, MA Katsunori Tanaka Transplantation Research Center, Brigham and Women’s Hospital, Harvard Medical School, Boston, MA Susan P. Shea Transplantation Unit, Surgical Services, Massachusetts General Hospital, Harvard Medical School, Boston, MA Reza Abdi Transplantation Research Center, Brigham and Women’s Hospital, Harvard Medical School, Boston, MA