title: Novel C1q assay reveals a clinically relevant subset of human leukocyte antigen antibodies independent of immunoglobulin G strength on single antigen beads.
abstract: It has been known for 40 years that cytotoxic human leukocyte antigen (HLA) antibodies are associated with graft rejection. However, the complement-dependent cytotoxicity assay (CDC) used to define these clinically deleterious antibodies suffers from a lack of sensitivity and specificity. Recently, methods exploiting immunoglobulin G (IgG) antibody binding to HLA single antigen beads (SAB) have overcome sensitivity and specificity drawbacks but introduced a new dilemma: which of the much broader set of antibodies defined by these methods are clinically relevant. To address this, we developed a complement-fixing C1q assay on the HLA SAB that combines sensitivity, specificity, and functional potential into one assay. We compared the CDC, IgG, and C1q assays on 96 sera having 2,118 defined antibodies and determined that CDC detects only 19% of complement-fixing antibodies detected by C1q, whereas C1q detects only 47% of antibodies detected by IgG. In the same patient, there is no predictability by IgG mean fluorescence intensity (MFI) as to which of the antibodies will bind C1q because fixation is independent of MFI values. In 3 clinical studies, C1q(+) antibodies appear to be more highly correlated than those detected by IgG alone for antibody-mediated rejection in hearts as well as for kidney transplant glomerulopathy and graft failure.
authors.affiliation: Department of Pathology, Stanford University School of Medicine, Palo Alto, CA 94304, USA.
authors.forename: G
authors.initials: G
authors.lastname: Chen
authors.forename: F
authors.initials: F
authors.lastname: Sequeira
authors.forename: D B
authors.initials: DB
authors.lastname: Tyan
mesh_terms: D000918:Antibody Specificity / Q000276:immunology*; D015415:Biomarkers / Q000097:blood; D015922:Complement C1q / Q000032:analysis* / Q000276:immunology; D006084:Graft Rejection / Q000175:diagnosis / Q000276:immunology; D006680:HLA Antigens / Q000097:blood* / Q000276:immunology; D016027:Heart Transplantation / Q000276:immunology* / Q000473:pathology; D006801:Humans; D007074:Immunoglobulin G / Q000097:blood / Q000276:immunology; D007075:Immunoglobulin M / Q000097:blood / Q000276:immunology; D007163:Immunosorbent Techniques; D007518:Isoantibodies / Q000097:blood* / Q000276:immunology; D016030:Kidney Transplantation / Q000276:immunology* / Q000473:pathology; D008163:Luminescent Measurements / Q000295:instrumentation; D011379:Prognosis; D011485:Protein Binding; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity
chemical_list: D015415:Biomarkers; D006680:HLA Antigens; D007074:Immunoglobulin G; D007075:Immunoglobulin M; D007518:Isoantibodies; D015922:Complement C1q