Identified HLA class I epitopes can undergo conformational induced variation due to changes within HLA bound peptides

Specificity of HLA monoclonal antibodies and their use to determine HLA expression on lymphocytes and peripheral blood stem cells

HLA Class I and II expression are known to differ locus-to-locus, however, HLA expression on the cell-surface is frequently reported as the total amount of HLA Class I or II antigens. This is despite evidence that indicates the differential expression of HLA can influence patient outcomes post-transplantation. Although numerous commercially available HLA monoclonal antibodies (mAbs) exist to characterize HLA expression, there is currently a lack of detailed information regarding their reactivities to HLA specificities. The specificities of locus-specific HLA mAbs (nine Class I and four Class II mAbs) were evaluated by two solid-phase Luminex single antigen bead assays. The reactivity patterns of these mAbs were then confirmed by flow cytometry using lymphocytes and PBSCs (peripheral blood stem cells). Out of the 13 HLA mAbs tested, only four (one Class I and three Class II mAbs) displayed intra-locus reactivity without also reacting to inter-locus specificities. Epitope analysis revealed the presence of shared epitopes across numerous HLA loci, explaining much of the observed inter-locus reactivity. The specificity of the HLA mAbs seen in solid-phase assays was confirmed against PBSCs and lymphocytes by flow cytometry. Using this method, we observed differences in the cell surface expression of HLA-C, HLA-DR, HLA-DQ, and HLA-DP between PBSCs and lymphocytes. Our results emphasize the need to characterize the reactivity patterns of HLA mAbs using solid-phase assays before their use on cells. Through understanding the reactivity of these HLA mAbs, the cellular expression of HLA can be more accurately assessed in downstream assays.

Reflections on HLA Epitope-Based Matching for Transplantation

HLA antibodies are primary causes of transplant rejection; they recognize epitopes that can be structurally defined by eplets. There are many reviews about HLA epitope-based matching in transplantation. This article describes some personal reflections about epitopes including a historical perspective of HLA typing at the antigen and allele levels, the repertoires of antibody-verified HLA epitopes, the use of HLAMatchmaker in determining the specificities of antibodies tested in different assays, and, finally, possible strategies to control HLA antibody responses.

Antibody-reactive class I epitopes defined by pairs of mismatched eplets and self-eplets

The identification of human leukocyte antigen (HLA) antibodies in the sera of candidates awaiting organ transplantation has evolved over time. This has been possible because of the introduction of more sensitive techniques and to the increasing focus on the structural aspects of the HLA epitopes. The use of the HLAMatchmaker algorithm in the analysis of positive sera and the verification of HLA ABC epitopes in the HLA Epitope Registry website provide new stimuli on the interpretation of antibody reactivity. The epitopes defined by eplet pairs often involve a nonself-eplet and a self-eplet (nonself-self paradigm), suggesting that the antibody response to an HLA mismatch must have an auto-reactive component. Here, we report an application of the nonself-self paradigm that provides a basis for better knowledge and interpretation of HLA-antibody reactivity in Luminex assays with single alleles.