Identification of mimotopes for the H4 minor histocompatibility antigen

The H4 minor histocompatibility antigen (HA) of mice includes a singleimmunogenic peptide presented by H-2Kb molecules that stimulates skinallograft rejection and is immunodominant in the stimulation of cytolytic Tlymphocytes (CTL) specific for multiple minor HA. We have identified H4mimotopes that are recognized by the H4-specific M9 CTL clone through theuse of a random peptide library comprised of bacterial clones expressing aninducible fusion protein tailed with the octamer sequence SXIXFXXL. Eightdiscrete mimotopes were identified that sensitized RMA-S cells for lysis byM9 CTL down to concentrations of 10(-11) M. Comparable reactivity wasobserved with a short-term, H4- specific CTL line indicating that themimotopes were not solely specific for the selecting M9 clone. Allmimotopes included Gly at p2 and either Val or Ile at p4, suggesting arequirement for a hydrophobic residue with specific conformation. Allmimotopes included either Arg or His at p7, implicating a requirement for aspecific positively charged amino acid at that position. The sixth positionwas more variable with four of eight mimotopes having a Val residue withsingle mimotopes including alternative amino acids, the majority of whichwere hydrophobic. Analysis of mimotopes for hydrophobicity and charge byreverse-phase HPLC and capillary electrophoresis respectively indicatedthat (i) mimotopes with Val at both p4 and p6 were hydrophobically similar(but not identical) to the natural H4 peptide, and (ii) a S --> Esubstitution at p1 resulted in a peptide (EGIVFVRL) with chargecharacteristics equivalent to those of the natural H4 peptide.