title: Activation of the lectin pathway of complement in pig-to-human xenotransplantation models.
abstract: BACKGROUND
  Natural IgM containing anti-Gal antibodies initiates classic pathway complement activation in xenotransplantation. However, in ischemia-reperfusion injury, IgM also induces lectin pathway activation. The present study was therefore focused on lectin pathway as well as interaction of IgM and mannose-binding lectin (MBL) in pig-to-human xenotransplantation models.
  
  
  METHODS
  Activation of the different complement pathways was assessed by cell enzyme-linked immunosorbent assay using human serum on wild-type (WT) and α-galactosyl transferase knockout (GalTKO)/hCD46-transgenic porcine aortic endothelial cells (PAEC). Colocalization of MBL/MASP2 with IgM, C3b/c, C4b/c, and C6 was investigated by immunofluorescence in vitro on PAEC and ex vivo in pig leg xenoperfusion with human blood. Influence of IgM on MBL binding to PAEC was tested using IgM depleted/repleted and anti-Gal immunoabsorbed serum.
  
  
  RESULTS
  Activation of all the three complement pathways was observed in vitro as indicated by IgM, C1q, MBL, and factor Bb deposition on WT PAEC. MBL deposition colocalized with MASP2 (Manders' coefficient [3D] r=0.93), C3b/c (r=0.84), C4b/c (r=0.86), and C6 (r=0.80). IgM colocalized with MBL (r=0.87) and MASP2 (r=0.83). Human IgM led to dose-dependently increased deposition of MBL, C3b/c, and C6 on WT PAEC. Colocalization of MBL with IgM (Pearson's coefficient [2D] rp=0.88), C3b/c (rp=0.82), C4b/c (rp=0.63), and C6 (rp=0.81) was also seen in ex vivo xenoperfusion. Significantly reduced MBL deposition and complement activation was observed on GalTKO/hCD46-PAEC.
  
  
  CONCLUSIONS
  Colocalization of MBL/MASP2 with IgM and complement suggests that the lectin pathway is activated by human anti-Gal IgM and may play a pathophysiologic role in pig-to-human xenotransplantation.
authors: 1 Department of Clinical Research, University of Bern, Bern, Switzerland. 2 Graduate School for Cellular and Biomedical Sciences, University of Bern, Bern, Switzerland. 3 Clinic of Plastic and Hand Surgery, Bern University Hospital, Bern, Switzerland. 4 Clinic of Cardiovascular Surgery, Bern University Hospital, Bern, Switzerland. 5 Molecular Animal Breeding and Biotechnology, Gene Center and Department of Veterinary Sciences, LMU Munich, Germany. 6 Revivicor, Inc., Blacksburg, VA. 7 Division of Immunology and Allergology, University Hospital and Medical Faculty, Geneva, Switzerland. 8 Address correspondence to: Robert Rieben, Ph.D., Department of Clinical Research, University of Bern, Murtenstrasse 50, P.O. Box 44, CH-3010 Bern, Switzerland.
authors: Anjan K
authors: AK
authors: Bongoni
authors: David
authors: D
authors: Kiermeir
authors: Hansjörg
authors: H
authors: Jenni
authors: Annegret
authors: A
authors: Wünsch
authors: Andrea
authors: A
authors: Bähr
authors: David
authors: D
authors: Ayares
authors: Jörg D
authors: JD
authors: Seebach
authors: Eckhard
authors: E
authors: Wolf
authors: Nikolai
authors: N
authors: Klymiuk
authors: Mihai A
authors: MA
authors: Constantinescu
authors: Esther
authors: E
authors: Vögelin
authors: Robert
authors: R
authors: Rieben
mesh_terms: D000818:Animals; D030801:Animals, Genetically Modified; D001803:Blood Transfusion; D002478:Cells, Cultured; D037582:Complement Pathway, Mannose-Binding Lectin; D003165:Complement System Proteins / Q000378:metabolism; D042783:Endothelial Cells / Q000276:immunology / Q000378:metabolism*; D005700:Galactosyltransferases / Q000172:deficiency / Q000235:genetics / Q000276:immunology; D006614:Hindlimb; D006648:Histocompatibility; D006801:Humans; D007075:Immunoglobulin M / Q000378:metabolism; D037241:Mannose-Binding Lectins / Q000276:immunology / Q000378:metabolism*; D050606:Mannose-Binding Protein-Associated Serine Proteases / Q000378:metabolism; D051916:Membrane Cofactor Protein / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D018482:Muscle, Skeletal / Q000098:blood supply* / Q000276:immunology / Q000378:metabolism; D013552:Swine; D013997:Time Factors; D014183:Transplantation, Heterologous
chemical_list: C497857:CD46 protein, human; D007075:Immunoglobulin M; D037241:Mannose-Binding Lectins; D051916:Membrane Cofactor Protein; D003165:Complement System Proteins; D005700:Galactosyltransferases; C530267:alpha-1,3-galactosyltransferase 1, porcine; D050606:Mannose-Binding Protein-Associated Serine Proteases