Recruitment of alloreactive cytotoxic T lymphocytes by an antigenic peptide.

To investigate the requirements for induction of cytotoxic T lymphocytes (CTL) by peptides we chose the 16-residue nucleoprotein peptide (NPP; 365-380) from the influenza virus A/NT/60/68 as model substrate that is recognized in conjunction with major histocompatibility complex H-2d. Here we present that CTL can be raised from naive animals by repeated in vitro stimulation with high concentrations of peptide. The frequency of this response can be boosted by immunization of the animals with NPP-conjugated to ovalbumin as a carrier. However, in contrast to NPP-specific CTL lines raised from virus-primed animals none of the peptide-induced CTL lines were able to lyse virus-infected targets. Although they did not show an apparent difference in fine specificity of the peptide recognized, their affinity to the target cells was 100-fold lower than that of CTL from virus-primed animals as estimated from the peptide concentration needed to achieve significant lysis. In addition, the activity of peptide-induced CTL was very sensitive to blocking by anti-CD8 antibodies as compared to virus-specific CTL. Furthermore, all peptide-induced CTL showed a high second reactivity for allogeneic H-2k targets. Therefore, it is argued that high epitope density achieved by high peptide concentrations can in vitro recruit lymphocytes of another specificity. For the tested peptide the reactive T lymphocytes showed high alloreactivity.