Interaction of in vitro- and in vivo-generated cytotoxic T cells with SV40 T antigen: analysis with synthetic peptides.

Abstract

Virus-specific cytotoxic T cells recognize antigens in the form of peptides (8 or 9 amino acids long) bound to MHC class-I molecules. Exposure of unprimed murine splenocytes to synthetic peptides of viral antigens elicits primary CTL in vitro. The fine specificity of such CTL as well as the correlation between binding affinity of peptides to class-I molecules and CTL induction was analysed using synthetic peptides corresponding to overlapping and distinct amino-acid residues in SV40 T antigen (Tag) Db-restricted T-cell epitopes I, II-III, and V. The peptides induced cross-reactive CD8+ primary CTL in splenocytes of naive C57 BL/6 mice. This reactivity was seen regardless of the peptides allelic anchor motifs or their abilities to stabilize empty class-I molecules. However, none of the primary CTL and CTL lines lysed Tag-expressing cells. In contrast, CTL generated in vivo by immunizing mice with Tag-expressing cells recognized endogenously processed Tag as well as synthetic peptides. The peptides recognized by these CTL depended on the intracellular concentration of Tag antigen in the immunizing cells. The reactivity of these CTL was peptide specific as shown by a functional peptide competition assay. Moreover, three peptides bound to and were recognized in the context of both Kb and Db molecules. These results have revealed a flexible disposition of MHC class-I molecules with regard to peptide binding and also reflected lack of correlation between binding affinity to class-I molecules and the capacity of peptides to induce primary CTL or to serve as potential targets. The significance of these findings in relation to identifying major T-cell epitopes using allele specific peptide motif and in vitro maintained CTL clones is discussed.