HU-023

In this study, the DR and DQ molecules from three different HLA-D clusters; HLA-Dw4, DKT2, and Dw15, associated with HLA-DR4 were analysed using monoclonal antibodies and two-dimensional gel electrophoresis. The results of serological analyses of specificity, sequential coprecipitation assays, and two-dimensional gel analyses showed that two monoclonal antibodies, HU-18 and HU-23 recognize two distinct antigenic epitopes borne on DQw3 molecules. In two-dimensional gel analysis, the DR4 light chains from ER (DR4, DQw3, Dw4 homozygous), KT2 (DR4, DQw3, DKT2 homozygous), and EBV-Wa (DR4, DQ--, Dw15 homozygous) cells were clearly different from each other in terms of their isoelectric points. Similary, the DQw3 light chains from ER and KT2 cells were also electrophoretically different. Moreover, it was indicated that DQw3 molecules from four different B cell lines being typed in a single cluster of HLA-Dw4 specificity differ in the serological reactivity with HU-23. These results suggested that DR molecules are the major component participating in the determination of the HLA-D specificity.

In a previous study, we showed that the three hitherto serologically indistinguishable HLA-D specificities associated with HLA-DR4, HLA- DYT , HLA- DKT2 , and HLA-Dw4 can be distinguished on the basis of their reactivity with two distinct Ia-like-specific monoclonal antibodies, HU-18 and HU-23. In this study, we attempted to identify and characterize Ia-like molecules recognized by HU-18 and HU-23 on a molecular level because Ia subsets (HLA-DR, MB, MT, or SB) identified by them remained unknown. The results of sequential coprecipitation assays and two-dimensional gel analyses showed that both HU-18 and HU-23 recognize antigenic determinants borne on MB3 but not on HLA-DRw6.2 molecules. Because the two monoclonal antibodies, specific for determinants carried on MB3 molecules, show distinct reactivity against homozygous typing cells defining HLA- DYT , HLA- DKT2 , and HLA-Dw4, all of which share DR4- MB3 , the data indicate that these three HLA-D clusters associated with HLA-DR4 possess distinct MB3 molecules, suggesting the existence of polymorphism in MB3 antigens.