title: Macrophage depletion prolongs discordant but not concordant islet xenograft survival.
abstract: BACKGROUND
  T cells and macrophages play a major role in the rejection of xenografted islets. Depending on the phylogenetic disparity, direct or indirect antigen presentation is predominant. The aim of this study was to analyze in vitro the predominance of direct or indirect presentation by depleting antigen-presenting cells in concordant and discordant xenogeneic combinations. In vivo, we analyzed the effect of macrophage depletion on concordant and discordant islet xenograft survival to assess in which combination this strategy can be used as therapeutic tool.
  
  
  METHODS
  In vitro, we performed mouse anti-rat and anti-human mixed lymphocyte reactions (MLR) after depletion of responder or stimulator antigen-presenting cells by magnetic sorting. In vivo, streptozotocin-induced diabetic C57BL/6 mice were treated by gadolinium chloride (GdCl) to deplete macrophages, and rat or human islets were transplanted under the kidney capsule. Islet function was followed by glycemia, and xenografts were analyzed at regular intervals for histology and immunohistochemistry.
  
  
  RESULTS
  Mouse anti-rat MLR showed a predominant direct antigen presentation pathway, whereas in mouse anti-human MLR, direct and indirect pathways were similarly involved. Survival of rat islets was not modified by GdCl therapy. In contrast, survival of human islets was significantly prolonged in GdCl-treated mice. Macrophage infiltration was decreased in concordant and discordant GdCl-treated xenografts at day 4 compared with controls. At day 15, macrophage, CD4+, and CD8+ cell infiltration was similar in all groups.
  
  
  CONCLUSIONS
  Our results indicate that direct antigen presentation is dominant in the rejection mechanism of concordant islet xenografts and cannot be influenced by host macrophage depletion. Both direct and indirect antigen presentation are involved in rejection of discordant xenogeneic islets. Macrophage depletion should only be considered as therapeutic tool for discordant islet xenotransplantation.
authors.affiliation: Surgical Research Unit, Department of Surgery, University Hospital Geneva, Geneva, Switzerland.
authors.forename: Axel
authors.initials: A
authors.lastname: Andres
authors.forename: Christian
authors.initials: C
authors.lastname: Toso
authors.forename: Philippe
authors.initials: P
authors.lastname: Morel
authors.forename: Domenico
authors.initials: D
authors.lastname: Bosco
authors.forename: Pascal
authors.initials: P
authors.lastname: Bucher
authors.forename: Jose
authors.initials: J
authors.lastname: Oberholzer
authors.forename: Zoltan
authors.initials: Z
authors.lastname: Mathe
authors.forename: Gang
authors.initials: G
authors.lastname: Mai
authors.forename: Thomas
authors.initials: T
authors.lastname: Wekerle
authors.forename: Thierry
authors.initials: T
authors.lastname: Berney
authors.forename: Leo H
authors.initials: LH
authors.lastname: Bühler
mesh_terms: D000818:Animals; D005682:Gadolinium / Q000494:pharmacology; D006085:Graft Survival; D016381:Islets of Langerhans Transplantation; D007959:Lymphocyte Culture Test, Mixed; D008264:Macrophages / Q000502:physiology*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D010587:Phagocytosis; D051381:Rats; D017207:Rats, Sprague-Dawley; D013601:T-Lymphocytes / Q000276:immunology; D014183:Transplantation, Heterologous
chemical_list: D005682:Gadolinium; C038958:gadolinium chloride