IN-VIVO CTL INDUCTION WITH POINT-SUBSTITUTED OVALBUMIN PEPTIDES - IMMUNOGENICITY CORRELATES WITH PEPTIDE-INDUCED MHC CLASS-I STABILITY

Class I molecules are conformationally sensitive to peptide binding, prolonging the complex's half-life on the surface of the cell. By making a series of H2-K-b anchor motif amino acid point substitutions in the ovalbumin 257-264 octamer, we were able to analyse subtle changes in peptide binding, K-b stabilization and in vivo immunogenicity. The cell line RMA-S was used to determine peptide-dependent K-b stabilization under equilibrium and non-equilibrium binding conditions. Sixteen conservative and non-conservative amino acid substitutions were made at positions 3, 5 or 8 of the peptide. At 37 degrees C, K-b stabilization was differentially affected by these substitutions, with several substitutions severely affecting K-b surface expression. When the substituted peptides were used as immunogens to prime cytotoxic T lymphocytes (CTL) in vivo, each peptide's ability to stabilize K-b directly correlated with the intensity of specific CTL activation. We conclude that peptide class I stabilization is an important influencing factor in determining cell surface steady-state expression of these peptides and thus the breadth of CTL recruitment. These concepts may relate the phenomenon of immunodominance to cell surface-presented peptide steady-state levels and may also aid in peptide vaccine design.