In vivo CTL induction with point-substituted ovalbumin peptides: immunogenicity correlates with peptide-induced MHC class I stability

Abstract

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-Kb anchor motif amino acid point substitutions in the ovalbumin 257-264 octamer, we were able to analyse subtle changes in peptide binding, Kb stabilization and in vivo immunogenicity. The cell line RMA-S was used to determine peptide-dependent Kb 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, Kb stabilization was differentially affected by these substitutions, with several substitutions severely affecting Kb surface expression. When the substituted peptides were used as immunogens to prime cytotoxic T lymphocytes (CTL) in vivo, each peptide's ability to stabilize Kb 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.