OPTIMAL LYMPHOCYTIC CHORIOMENINGITIS VIRUS SEQUENCES RESTRICTED BY H-2D(B) MAJOR HISTOCOMPATIBILITY COMPLEX CLASS-I MOLECULES AND PRESENTED TO CYTOTOXIC T-LYMPHOCYTES

Infection with lymphocytic choriomeningitis virus induces the generation of CD8(+) cytotoxic T lymphocytes (CTL). In the H-2(b) mouse, this cellular immune response is directed against three viral structural epitopes (GP1, GP2, and NP) presented by the major histocompatibility complex (MHC) class I H-2D(b) molecules. This study was undertaken to delineate which sequence of each of these three epitopes is optimal for MHC binding and CTL recognition. The first step was to synthesize the relevant peptides truncated at the N or C terminus and flanking the crucial H-2D(b)-anchoring Asn residue in position 5. These peptides were then tested (i) for their binding properties in two H-2D(b)-specific assays with viable cells (upregulation of H-2D(b) expression on the surface of RMA-S cells and competition against the D-b-restricted peptide I-125-gp276-286 on T2-D-b cells) and (ii) for their abilities to sensitize H-2(b) target cells for CTL lysis in vitro. For optimal antigenic presentation, all three epitopes required the MHC-anchoring Asn residue at position 5 of their sequences. The results clearly and unambiguously delineated optimal lengths for two of the epitopes and two options for the third. NP appeared as a conventional 9-amino-acid (aa)-long peptide, np396-404 (FQPQNGQFI). GP2 was defined as a longer peptide (11 aa), gp276-286 (SGVENPGGYCL). Characterization of the GPI epitope was more complex: the 9-aa-long peptide gp33-41 (KAVYNFATC) and the carboxyl-extended 11-aa-long peptide gp33-43 (KAVYNFATCGI) were both established as possible optimal sequences depending on the cell line used to test binding and lysis.