T-CELL UNRESPONSIVENESS IN-VITRO CAN BE DUE TO ACTIVATION IN-VIVO

During investigations into the behaviour and fate of ovalbumin (OVA)-s pecific CD8(+) T cells in a TCR transgenic system, cytotoxic T lymphoc yte (CTL) activity (as measured by classical in vitro stimulation foll owed by Cr-51-release assay) was found to be reduced after OVA peptide administration, This paradoxically occurred even during the peak of a ctivation and expansion of these T cells, The reduced responsiveness o ccurred for both classical CTL assays and in vitro proliferation assay s, and would apparently be consistent with induction of anergic or sup pressor T cells. Instead, we provide evidence that in vivo peptide tre atment generated activated killers which consequently killed the stimu lator cells during in vitro culture, thus resulting in the unresponsiv e phenotype, In co-culture experiments, the proliferation and classica l CTL activity were severely reduced when naive OVA-specific CD8(+) T cells (OT-I) cells were co-cultured with cells from OVA peptide-treate d mice, Moreover, cells obtained after peptide injection did not requi re in vitro stimulation to be able to kill target cells. Therefore, ac tivation of killers in vivo should be considered as one pathway whereb y unresponsiveness is found in assays requiring in vitro stimulation.