ROTRF Recognition Prize – Recognising Excellence in Organ Transplantation Research

12:25: Role of Glycosaminoglycans in Regulation of Chemokine Activity during Transplantation

Dr Simi Ali, Newcastle University, Newcastle-upon-Tyne, UK

Chemokines recruit leukocytes during allograft rejection. It is thought that the formation of glycosaminoglycan (GAG)-stabilized chemokine concentration gradients within the allograft plays a crucial role in this process. We examined the role played by changes in the biology of GAG molecules within kidney sections during the development of episodes of acute renal allograft rejection. We were the first to provide the evidence that the abundance of N-sulphated domains in heparan sulphate (HS) increases within the tubular basement membrane and blood vessel walls during acute rejection. This increase correlated with a localized increase in expression of the chemokine CCL5. Significantly, both the endothelial cell surface in vitro and the tubular basement membrane in vivo showed an enhanced capacity to bind this chemokine during inflammation. Because leukocytes respond to immobilized chemokines, it is likely that the increased capacity to present chemokines at these sites plays a role in recruiting leukocytes from the blood and then in directing responsive cells to the tubules. It is possible that the critical interaction between chemokines and sulphated GAG species provides a potential site for anti-inflammatory intervention.

We further designed non-GAG-binding mutant CCL7 (mtCCL7), which retained its affinity for chemokine receptors. This mtCCL7 induced leukocyte chemotaxis in diffusion gradients but did not stimulate trans-endothelial migration. Unlike wild-type CCL7, mtCCL7 persisted in the circulation of BALB/c mice for more than 6 hours and prevented leukocyte infiltration of skin isografts. Treatment with mtCCL7 marginally increased the survival of C57BL/6 to BALB/c skin allografts and reduced graft infiltration by CD3+ cells. Importantly, mtCCL7 promoted long-term (>40 day) graft survival following minor histocompatibility (HY) antigen mismatched C57BL/6 skin transplantation; control grafts were rejected by day 24. Treatment with mtCCL7 produced a significant decrease in the frequency of IFN-γ producing donor-reactive splenic T cells, reduced CCR2 expression by circulating leukocytes for 6 hours, and blocked the normal increase in affinity of α4β1 integrins for VCAM-1 following transient chemokine stimulation. These data suggest that mtCCL7 persists in the circulation and reduces both specific T cell priming and the capacity of circulating immune cells to respond to GAG-bound chemokine at sites of developing inflammation.

Additional work was carried out with a non-GAG binding mutant-CXCL12. Intravenous administration of mtCXCL12 inhibited the recruitment of leukocytes to murine air pouches filled with wild-type CXCL12. Chronic exposure to mutant CXCL12 in the circulation reduced leukocyte-surface expression of CXCR4. In summary, sustained circulation of non-GAG binding mutant chemokines can down-regulate their specific receptors leading to homologous/heterologous desensitisation, which may have positive effect in solid allograft survival.

Figure 1: Minor histocompatibility antigen (HY) mismatched skin transplantation showing effect of mtCCL7 on HY skin graft survival. Female C57BL/6 mice were transplanted with male syngeneic skin and were either treated i.v. with saline, wild-type CCL7 or mtCCL7 at 20 µg/day for 6 days. Representative data are shown for one of two independent experiments; n=5 for each group.

Dr Simi Ali

Dr Simi Ali is currently a Reader in Immunobiology at the Institute of Cellular Medicine at Newcastle University in Newcastle-upon-Tyne, UK. Dr. Ali obtained her PhD in Biochemistry from Central Drug Research Institute in Lucknow, India and was a Commonwealth Post-doctoral Fellow in Molecular Biology at UMIST, Manchester, UK and in the Department of Biological Sciences at University of Newcastle-upon-Tyne. Since 1995 she has been lecturing at the University of Newcastle-upon-Tyne. She is a member of the British Society of Immunology and the British Transplantation Society. She is on the scientific panels for the Northern Counties Kidney Research Fund Scientific Sub-Committee and the NHS Grampian Endowment Fund. Dr. Ali has published over 50 peer-reviewed manuscripts and a book chapter, and has been an invited speaker at numerous conferences. She sits on the editorial board of The Open Transplantation Journal, Open Transplantation Reviews and Translational Biomedicine.