An allo-specific peptide derived from HLA-A2 is presented by HLA-DQ7

The peptide motifs of two HLA class II molecules, DR11 and DQ7, were determined from natural peptides. The EBV transformed B cells JVM (HLA-A2-DRB1^*1102-DQA1^*0501-DQB1^*0301) were cultured to a final yield of 2 10¹⁰ cells. DR11 and DQ7 molecules were immunopurified and peptides were extracted after acid elution and separated by reverse-phase HPLC. Five peptides from DR11 and five from DQ7 were sequenced using Edman degradation and other peptides were analysed by pool sequencing. Peptides were from 11 to 15 amino acids in length and P often occurred at the second residue for both DR5 and DQ7. The peptide motif for DR11 was I at position i and K or R at position i + 4. For DQ7 the most significant signal was A in the middle of the peptide as also described by Falk et al. The source of one peptide eluted from DQ7 was a polymorphic part of the HLA-A2 heavy chain (from 56th to 69th amino-acid). It was also exactly the same peptide than the synthetic peptide used by Krensky et al in the 10th international workshop to modulate lysis by HLA-A2-specific cytotoxic T lymphocytes. The biochemical characterisation of this peptide from HLA-DQ7 strongly supports functional tests showing an indirect presentation of alloantigens by MHC molecules.