TIC Publications
Our thought provoking publications highlight our progress and our commitment to discoveries and innovations that will lead to a better understanding of the mechanism of allograft rejection.
Featured articles:
Antigen quantity is responsible for the discrepancy between phenotype and single antigen beads for the detection of human leukocyte antigen DQ antibody: Potential clinical implications
N. Remi Shih1,† ∙ Thoa Nong1,† ∙ Robert A. Bray2 ∙ Cathi Murphey3 ∙ Ina Skaljic4 ∙ Howard M. Gebel2 ∙ Mayra Lopez-Cepero1 ∙ Peter W. Nickerson5 ∙ Jar-How Lee
Abstract
De novo donor-specific human leukocyte antigen DQ antibodies detected by single antigen beads (SAB) are significantly associated with chronic antibody-mediated rejection and lower overall graft survival. However, some DQ antibodies identified by SAB cannot be confirmed by phenotype antigen-bearing class II bead assays, raising concerns about the validity of SAB data. The inability to detect these antibodies on phenotype antigen beads could be due to a lower quantity of DQ antigens present on the surface of the beads compared to DR antigens. In this study, we demonstrate that DQ-enriched phenotype antigens exhibit the same reactivity with DQ antibodies detected by SAB, confirming the hypothesis that it is antigen quantity and not structural differences that account for discrepancies in human leukocyte antigen DQ antibody detection between phenotype antigen beads and SAB. In addition, we show that the expression of individual DQ antigens in heterozygous cells can vary significantly, further confounding correlation studies. Therefore, the common clinical practice of using the phenotype antigen beads as a screening assay, reflexing to SAB testing only when positive, may inadvertently fail to detect DQ-specific antibodies. Such errors could impact organ acceptance practices, immunosuppression treatment decisions, and/or the need for additional diagnostic testing to rule out antibody-mediated rejection.
HLA class I peptide polymorphisms contribute to class II DQβ0603:DQα0103 antibody specificity
N. Remi Shih, Thoa Nong, Cathi Murphey, Mayra Lopez-Cepero, Peter W. Nickerson, Jean-luc Taupin, Magali Devriese, Jakob Nilsson, Marie-Benedicte Matignon, Robert A. Bray & Jar-How Lee
Abstract
Antibodies reactive to human leukocyte antigens (HLA) represent a barrier for patients awaiting transplantation. Based on reactivity patterns in single-antigen bead (SAB) assays, various epitope matching algorithms have been proposed to improve transplant outcomes. However, some antibody reactivities cannot be explained by amino acid motifs, leading to uncertainty about their clinical relevance. Antibodies against the HLA class II molecule, DQβ0603:DQα0103, present in some candidates, represent one such example. Here, we show that peptides derived from amino acids 119-148 of the HLA class I heavy chain are bound to DQβ0603:DQα0103 proteins and contribute to antibody reactivity through an HLA-DM-dependent process. Moreover, antibody reactivity is impacted by the specific amino acid sequence presented. In summary, we demonstrate that polymorphic HLA class I peptides, bound to HLA class II proteins, can directly or indirectly be part of the antibody binding epitope. Our findings have potential important implications for the field of transplant immunology and for our understanding of adaptive immunity.
Identification of Antibodies to DQβ:DRα Interisotypic Heterodimers in Human Sera
Thoa Nong, BS, Nengjen Remi Shih, PhD, Robert A. Bray, PhD, Mayra Lopez-Cepero, PhD,
Cathi Murphey, PhD, Peter W. Nickerson, MD, and Jar-How Lee, PhD
Abstract
Background
HLA class II antigens, DR, DQ, and DP, comprised an α and β chains, which typically combine, within
the same isotype, to form the major histocompatibility complex:peptide complex. Interisotypic pairing is not commonly
observed. Although reports of DQβ:DRα heterodimers exist, the pairing was reported to be unstable and, therefore, not studied to any extent.
Methods
DQβ:DRα single antigens were produced through transfectant cell lines and used to identify
and characterize positive reactive human sera by a multiplex bead-based assay.
Results
Stable DQβ:DRα transfectants were constructed. Cell surface staining with class II–specific monoclonal antibodies revealed that some DQB1 alleles appear to be more efficient in expressing DQβ:DRα heterodimers. Interestingly, alleles within the same serological group varied in their efficiency of forming dimers on the cell surface. For example, DQβ0601:DRα had the highest transfection and cell membrane expression efficiency among 16 common DQB1 alleles tested. In contrast, DQβ0603:DRα-positive transfectants demonstrated minimal surface expression. Assembly of DQβ0601:DRα was not affected by the presence of a DQα chain. DQβ0601:DRα and DQβ0603:DRα single-antigen beads were used to screen human sera. Positive sera were identified that reacted to the unique epitopes of DQβ0601:DRα protein on the cell surface of the transfectants.
Conclusions
Our studies have demonstrated that unique DQβ:DRα heterodimers can be formed and are stably expressed on the cell surface. Such antigenic combinations, presented on single-antigen beads, demonstrated that patient sera can react with such heterodimers. Investigations on the potential clinical roles of antibodies against such interisotypic heterodimers are now possible.
(Transplantation 2024;00: 00–00).
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