Class ii major histocompatibility complex gene sequences in rheumatoid arthritis. The third diversity regions of both DRβ₁ genes in two DR1, DRw10–positive individuals specify the same inferred amino acid sequence as the DRβ₁ and DRβ₂ Genes of a DR4 (Dw14) haplotype

The DR1 and DRw10β₁, chain genes were isolated from each of 2 individuals with rheumatoid arthritis who were heterozygous for these class II major histocompatibility complex specificities. The sequences of the DR1β₁ chains from both patients were identical, differing from previously reported DRβ₁ chains of individuals without RA by 2 amino acid substitutions, at positions 85 (Val‐Ala) and 86 (Gly‐Val), and by a silent mutation at the last nucleotide of codon 78 (C–T), resulting in the loss of a Pst I restriction endonuclease site. Identical DRw10β₁, chain genes were found in both patients. These were shown to encode the epitope recognized by monoclonal antibody 109d6. This antibody also recognizes an epitope on the DRw53β₂ chain of the DR4 haplotype. The third diversity regions of the DR1β (amino acids 67–74) and the DRw10β₁ chains (amino acids 67–73) were identical, respectively, with those of the DR4 (Dw14) β₁, and β₂ chains, raising the possibility that in these patients, the third diversity regions of the two DRβ₁, chain genes present in trans are conformationally equivalent to the cis‐encoded third diversity regions of the DR4 (Dw14), DRβ₁, and β₂ chains. The nucleotide sequences of the DQβ complementary DNA clones were identical to that of the DQw1β chain, and no DRβ₂ complementary DNA clones were identified.