Jeremy Goodman

Activation of Natural Killer Cells and Macrophages by Porcine Endothelial Cells Augments Specific T-Cell Xenoresponse

The rejection of xenografts is characterized by infiltration of monocytes and natural killer (NK) cells into the graft, suggesting an important role for the innate immune system in xenorecognition. In this study, purified human NK or T cells were cocultured with porcine endothelial cells, and cytokines were analyzed by ELISA and intracellular FACS. We demonstrated a vigorous human anti‐porcine xenoresponse that was associated with a strong T‐cell proliferation against porcine endothelial cells. Limiting dilution cloning and T‐cell receptor (TCR) Vβ gene usage revealed a low number of xenoreactive T‐cell precursors. We demonstrated that xenogeneic porcine but not allogeneic human endothelial cells induced the early production of interferon (IFN)‐γ by human NK cells but not by CD3+ T cells. Porcine xenoantigen‐induced IFN‐γ production was only partially dependent on IL‐12. Blocking IL‐12 with neutralizing antibodies or by depletion of human macrophages partially decreased IFN‐γ production by CD56+ NK cells. Three‐color flow cytometry revealed that IL‐12 was produced through a species‐specific activation of human macrophages by porcine endothelial cells. Our results indicate that the direct activation of NK cells and macrophages by porcine endothelial cells provides a unique pathway of xenorecognition that augments downstream specific T‐cell immunity and represents a powerful effector mechanism in xenograft rejection.

Role of Intra-islet Endothelial Cells in Islet Allo-immunity

Background. Intra-islet endothelial cells (IECs) express high levels of major histocompatibility complex (MHC) and are pivotal for posttransplant islet revascularization. We postulated that donor-specific sensitization would result in hyperacute rejection of IECs and prevent islet engraftment. Furthermore, ligation of endothelial cells with subsaturating concentrations of anti-MHC class I antibody (Ab) results in “accommodation” conferring protection against Ab/complement-mediated lysis. Therefore, we investigated whether accommodation of IECs would prevent hyperacute rejection of islets in sensitized recipients. Methods. Islets were transplanted beneath the kidney capsule and allograft survival monitored using daily blood glucose (diabetes >300 mg/dL, normoglycemia <150 mg/dL). Recipients were presensitized with donor islets, splenocytes, or skin. Accommodation was induced by incubating human or murine islets with varying concentrations of anti-MHC class I Ab ex vivo. Results. Isografts remained functional for >100 days, whereas allografts were rejected by day 14. Islet allo-transplantation induced donor-specific but not third-party anti-MHC Abs. Donor-specific, but not third-party, sensitization induced hyperacute rejection of subsequent islet allografts (median survival 1 day) associated with complement deposition. Preincubation of islets with subsaturating concentrations of anti-MHC-I Abs (1–100 ng/mL) up-regulated Bcl-2, Bcl-xl, and HO-1 within CD31+ IEC. These accommodated islets were resistant against hyperacute rejection when transplanted into donor-(splenocyte) sensitized recipients without any immunosuppression (median survival 6 days). Conclusions. Pretransplant sensitization against donor antigens results in hyperacute rejection of murine islets. IECs may play a crucial role in development of donor-specific immunity after islet transplantation. Significantly, accommodation of IEC may confer resistance to hyperacute rejection in sensitized recipients.