Alterations of a dominant epitope of lymphocytic choriomeningitis virus which affect class I binding and cytotoxic T cell recognition

We have investigated mutation of a dominant cytotoxic T cell (CTL) epitope from the nucleoprotein (NP) of lymphocytic choriomeningitis virus (LCMV). Five NP peptide analogs with single substitutions at the predicted anchor residues (designated by the wild type amino acid, the position number and the new amino acid: P2A, P2R, M9L and M9K) and at a non-anchor position (S5N) were examined for binding to class I, H-2 L^d molecules. Each of the substitutions decreased or abolished the capacity of the NP peptide to increase cell surface L^d expression and to induce L^d stabilization in the cell lysates, indicating that these substitutions significantly affected peptide binding to L^d. We tested the peptide analogs for recognition by bulk primary CTL specific for LCMV, and for their ability to stimulate in vitro the CTL originally induced by wild type LCMV. Except for the M9L change, all mutations reduced CTL recognition by at least 100-fold, and the analogs failed to stimulate the CTL in vitro. The M9L peptide was recognized by the CTL and stimulated the CTL in vitro almost as well as wild type; however, this peptide induced L^d stabilization in the cell lysates to a much lesser extent than wild type. Overall, this study demonstrates that mutations in the NP epitope affected peptide binding to the L^d molecule and CTL recognition.