Arthritogenic peptide binding to DRB1*01 alleles correlates with susceptibility to rheumatoid arthritis

Genetic susceptibility to rheumatoid arthritis (RA) is often defined by the presence of a shared epitope (QKRAA, QRRAA, or RRRAA) at positions 70-74 in HLA-DRβ1. However, DRβ1*01:01 and 01:02 contain the same QRRAA epitope, but differ considerably in their susceptibility to RA. The purpose of this study was to determine if this difference could be explained by their ability to bind three arthritogenic peptides that we have previously shown to bind to the archetypal RA-susceptible allele, DRβ1*04:01, but not to the resistant DRβ1*08:01 allele. Binding of type II collagen(258-272), citrullinated and native vimentin(66-78), and citrullinated and native α-enolase(11-25) were measured on cell lines expressing either DRβ1*01:01, *01:02 or *01:03 in association with DRα1*01:01. DRβ1*01:01 and *01:02 both exhibited a 6.5-fold preference for citrullinated vimentin(66-78) compared to native vimentin. However, DRβ1*01:01 also exhibited a 1.7-fold preference for citrullinated α-enolase(11-25) and bound collagen(258-272), while DRβ1*01:02 bound neither of these peptides. Consistent with its known resistance to RA, DRβ1*01:03 preferentially bound native vimentin(66-78) and α-enolase(11-25) over the citrullinated forms of these peptides, and also failed to bind collagen(258-272). Site-directed mutagenesis was performed to determine which amino acid residues were responsible for the differences between these alleles. Mutating position 86 in DRβ1*01:01 from glycine to the valine residue found in DRβ1*01:02 eliminated binding of both citrullinated α-enolase(11-25) and collagen(258-272), thereby recapitulating the peptide-binding profile of DRβ1*01:02. The difference in susceptibility to rheumatoid arthritis between DRβ1*01:01 and *01:02 thus correlates with the effect of position 86 on the binding of these arthritogenic peptides. Consistent with their association with RA resistance, positions I67, D70 and E71 all contributed to the inability of DRβ1*01:03 to bind these arthritogenic peptides.