title: In vitro detection of C4d-fixing HLA alloantibodies: associations with capillary C4d deposition in kidney allografts.
abstract: Capillary C4d deposition is a valuable marker of antibody-mediated rejection (AMR). In this analysis, flow cytometric detection of alloantibody-triggered C4d deposition to HLA antigen-coated microparticles ([C4d]FlowPRA) was evaluated for its value as a marker for C4d deposition in renal allografts. For comparative analysis, 105 first renal biopsies performed for graft dysfunction and an equal number of concurrent sera were subjected to immunohistochemistry and [C4d] plus standard [IgG]FlowPRA, respectively. C4d deposition/fixation was detected in 17 biopsies and, applying [C4d]FlowPRA HLA class I and II screening, also in a small number of corresponding sera (N = 20). IgG reactivity detected by standard [IgG]FlowPRA was more frequent (49% of sera). Comparing [C4d]FlowPRA screening with capillary C4d staining, we found a high level of specificity (0.92 [95% confidence interval: 0.86-0.98]), which far exceeded that calculated for [IgG]FlowPRA (0.60 [0.50-0.70]). [IgG]FlowPRA screening, however, turned out to be superior in terms of sensitivity (0.94 [0.83-1.05] vs. 0.76 [0.56-0.97] calculated for C4d-fixing panel reactivity). Remarkably, posttransplant single antigen testing for identification of complement-fixing donor-specific alloreactivities failed to improve the predictive value of FlowPRA-based serology. In conclusion, our results suggest that detection of complement-fixing HLA panel reactivity could provide a specific tool for monitoring of C4d-positive AMR.
authors.affiliation: Division of Nephrology and Dialysis, Department of Medicine III, Medical University of Vienna, Vienna, Austria.
authors.forename: G
authors.initials: G
authors.lastname: Bartel
authors.forename: M
authors.initials: M
authors.lastname: Wahrmann
authors.forename: M
authors.initials: M
authors.lastname: Exner
authors.forename: H
authors.initials: H
authors.lastname: Regele
authors.forename: N
authors.initials: N
authors.lastname: Huttary
authors.forename: M
authors.initials: M
authors.lastname: Schillinger
authors.forename: G F
authors.initials: GF
authors.lastname: Körmöczi
authors.forename: W H
authors.initials: WH
authors.lastname: Hörl
authors.forename: G A
authors.initials: GA
authors.lastname: Böhmig
mesh_terms: D000328:Adult; D002196:Capillaries / Q000276:immunology / Q000378:metabolism; D015935:Complement C4b / Q000378:metabolism*; D003168:Complement Fixation Tests; D005260:Female; D006680:HLA Antigens / Q000276:immunology*; D006801:Humans; D007518:Isoantibodies / Q000032:analysis* / Q000502:physiology; D007668:Kidney / Q000098:blood supply* / Q000276:immunology / Q000378:metabolism*; D016030:Kidney Transplantation / Q000276:immunology*; D008297:Male; D008875:Middle Aged; D010446:Peptide Fragments / Q000378:metabolism*; D014184:Transplantation, Homologous
chemical_list: D006680:HLA Antigens; D007518:Isoantibodies; D010446:Peptide Fragments; D015935:Complement C4b; C032261:complement C4d