Immunogenicity of two peptide determinants in the cytolytic T-cell response to flavivirus infection: Inverse correlation between peptide affinity for MHC class I and T-cell precursor frequency

We used the CD8⁺ cytotoxic T (Tc) cell immune response against the flavivirus, Murray Valley encephalitis virus (MVE), restricted by the H-2K^k major histocompatibility complex (MHC) class I molecule, to investigate immunodominance. Split-clone limiting dilution analysis revealed almost exclusive recognition of two peptides, MVE₁₇₈₅ and MVE₁₉₇₁, derived from the viral NS3 protein. The precursor frequency of MVE-reactive Tc cells was determined by limiting dilution analysis for cytotoxic function and intracellular staining for interferon-γ; the latter gave a 100-fold higher estimate of MVE-reactive Tc cell precursors. MHC class I cell surface stabilization assays revealed that affinity for H-2K^k as well as half-lives of the peptide-H-2K^k-complexes were markedly different for the two peptides. However, a kinetic study of antigen presentation showed that both peptides are presented for recognition by Tc cells with a comparable kinetics during the latent period of virus infection. Nevertheless, the lower affinity peptide MVE₁₇₈₅ elicited roughly twofold more Tc cell clones than the high-affinity peptide MVE₁₉₇₁. While the cytolytic activity against both determinants was similar after in vitro restimulation at the peak of the primary response, the smaller pool of memory anti-MVE₁₉₇₁ Tc cells correlated with an impaired memory response against that determinant, suggesting that the available T-cell repertoire is a major factor influencing the establishment of T-cell memory.