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).