Transfer of polymorphic monoclonal antibody epitopes to the first and second domains of HLA-DR β-chains by site-directed mutagenesis

We used site-directed mutagenesis of HLA-DR β-chains to localize the binding sites for two polymorphic DR-binding mAb to residues in the first and second external domains, respectively. Transfer of three first domain α-helical residues, G73, R74 and N77, normally present in DR3a and DRw52a, to a DR4 β-chain was sufficient for recognition of this mutant DR molecule by a DR3-specific mAb, NDS 9. A polymorphism controlling the binding of a DR4-specific mAb, GS 359-13F10, was mapped to a tyrosine at position 96 of the DR4 β-chain second domain by the construction of a chimeric DR molecule containing a DR2-first domain and DR4-second domain. The mapping of these two polymorphic epitopes to specific positions on the DR β-chain will allow further structural and functional analysis of the DR molecule.