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

We used the CD8(+) cytotoxic T (Tc) cell immune response against the flaviv irus, Murray Valley encephalitis virus (MVE), restricted by the H-2K(k) maj or histocompatibility complex (MHC) class I molecule, to investigate immuno dominance. Split-clone limiting dilution analysis revealed almost exclusive recognition of two peptides, MVE1785 and MVE1971, derived from the viral N S3 protein. The precursor frequency of MVE-reactive Tc cells was determined by limiting dilution analysis for cytotoxic function and intracellular sta ining for interferon-gamma; the latter gave a 100-fold higher estimate of M VE-reactive Tc cell precursors. MHC class I cell surface stabilization assa ys 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 present ed for recognition by Tc cells with a comparable kinetics during the latent period of virus infection. Nevertheless, the lower affinity peptide MVE178 5 elicited roughly twofold more Tc cell clones than the high-affinity pepti de MVE1971 While the cytolytic activity against both determinants was simil ar after in vitro restimulation at the peak of the primary response, the sm aller pool of memory anti-MVE1971 Tc cells correlated with an impaired memo ry response against that determinant, suggesting that the available T-cell repertoire is a major factor influencing the establishment of T-cell memory .