Length and subpeptidome distribution of HLA-B*51 ligands.
A, the B*51:08 ligands with Pro-2/Ala-2 and Ile/Val at PΩ from the LCL BCH-30 (black) were classified by length and compared with the equivalent set of previously reported B*51:01 ligands from 721.221 transfectant cells (25) with the same motif (white). A total of 624 and 1271 peptides from B*51:08 and B*51:01, respectively, were included. B, comparison of the Pro-2 and Ala-2 subpeptidomes. A total of 285 and 833 peptides with Pro-2 and 339 and 438 peptides with Ala-2 from B*51:08 and B*51:01, respectively, were included. C, percent residue frequency at P2 of B*51:08 ligands (8–12 residues) from BCH-30 cells (black) with Pro-2/Ala-2 + Val/Ile at PΩ (n = 624), compared with the equivalent set of previously identified B*51:01 ligands (n = 1271) from 721.221-B*51:01 transfectant cells (white). Statistically significant differences, assessed by the χ2 test, and their p values are shown.