Table 1.
HLA–DRB1 amino acid sequence for alleles observed among rheumatoid arthritis patients and their classification according to du Montcel and colleagues
| HLA-DRB1 allele | Amino acid position | Classification of du Montcel and colleagues | |||||||
| 69 | 70 | 71 | 72 | 73 | 74 | 75 | 76 | ||
| HLA-DRB1*0101 | E | Q | R | R | A | A | V | D | S3P |
| HLA-DRB1*0102 | - | Q | R | R | A | A | - | - | S3P |
| HLA-DRB1*0103 | - | D | E | R | A | A | - | - | S1 |
| HLA-DRB1*03 | - | - | K | - | G | R | - | - | X |
| HLA-DRB1*0401 | - | Q | K | R | A | A | - | - | S2 |
| HLA-DRB1*0402 | - | D | E | R | A | A | - | - | S1 |
| HLA-DRB1*0403 | - | - | - | - | - | E | - | - | X |
| HLA-DRB1*0404 | - | Q | R | R | A | A | - | - | S3P |
| HLA-DRB1*0405 | - | Q | R | R | A | A | - | - | S3P |
| HLA-DRB1*0407 | - | - | - | - | - | E | - | - | X |
| HLA-DRB1*0408 | - | Q | R | R | A | A | - | - | S3P |
| HLA-DRB1*0411 | - | - | - | - | - | E | - | - | X |
| HLA-DRB1*07 | - | D | - | - | G | Q | - | - | X |
| HLA-DRB1*08 | - | D | - | - | - | L | - | - | X |
| HLA-DRB1*0901 | - | R | - | - | - | E | - | - | X |
| HLA-DRB1*1001 | - | Q | R | R | A | A | - | - | S3P |
| HLA-DRB1*1101 | - | D | R | R | A | A | - | - | S3D |
| HLA-DRB1*1102 | - | D | E | R | A | A | - | - | S1 |
| HLA-DRB1*1103 | - | D | E | R | A | A | - | - | S1 |
| HLA-DRB1*1104 | - | D | R | R | A | A | - | - | S3D |
| HLA-DRB1*12 | - | D | R | R | A | A | - | - | S3D |
| HLA-DRB1*1301 | - | D | E | R | A | A | - | - | S1 |
| HLA-DRB1*1302 | - | D | E | R | A | A | - | - | S1 |
| HLA-DRB1*1303 | - | D | K | R | A | A | - | - | S2 |
| HLA-DRB1*1323 | - | D | E | R | A | A | - | - | S1 |
| HLA-DRB1*1401 | - | R | - | - | - | E | - | - | X |
| HLA-DRB1*1402 | - | Q | R | R | A | A | - | - | S3P |
| HLA-DRB1*1404 | - | R | - | - | - | E | - | - | X |
| HLA-DRB1*15 | - | Q | A | R | A | A | - | - | S1 |
| HLA-DRB1*16 | - | D | R | R | A | A | - | - | S3D |
In the du Montcel and colleagues classification [35], the HLA–DRB1 alleles were first divided into two groups according to the presence or absence of the RAA sequence at positions 72–74, which denote S and X alleles (respectively shared epitope and nonshared epitope alleles). The S alleles were subsequently divided into four groups according to the two first amino acids at positions 70 and 71 (boldface): S1 for ARAA and ERAA, S2 for KRAA, S3 for RRAA (divided into S3P for QRRAA and S3D for DRRAA according to position 70), and X for all non-RAA motifs. The conventional classification of the amino acids was used, here divided into three biochemical subgroups, as follows: group 1 = G for glycine, A for alanine, V for valine, L for leucine (aliphatic amino acids (nonpolar hydrophobic)); group 2 = K for lysine, R for arginine (basic amino acids (polar and positively charged)); group 3 = E for glutamic acid, Q for glutamine (the amide corresponding to E), D for aspartic acid, and N for asparagine (the amide corresponding to D) (acidic amino acids and corresponding amides are very hydrophilic; acidic amino acids are polar and negatively charged at physiologic pH, amides are polar and uncharged, and not ionizable) [36].