Fig. 1.

Failure of Prf-deficient CD8⁺ CTL to control an ECTV infection. B6.WT and B6.Prf^−/− mice were infected i.v. with 5 × 10⁵ PFU of avirulent ECTV-TK⁻. Five days later mice were killed, and splenic CD8⁺ T cells were enriched by using Dynabeads. Enriched CD8⁺ T cells (>80% purity) were injected i.v. into recipient B6.WT mice 24 h after infection with 5 × 10⁴ PFU of virulent ECTV. Groups of mice received 10⁷ cells of either population or no cells. (A) Viral titers in spleen and liver 4 days after infection and 3 days after cell transfer, as determined by viral plaque assays. *, P < 0.05; NS, not significant. (B) CTL activity of unfractionated splenocytes from the different recipients, 3 days after cell transfer, as measured by ⁵¹chromium release assay using uninfected and ECTV-infected MC57G fibrosarcoma target cells. (C) Clonal expansion of ECTV-specific CD8⁺ T cells in B6.WT and B6.Prf^−/− mice 5 days after ECTV infection. CD8⁺ T cells recognizing the immunodominant ECTV determinant (TSYKFESV) (12), encoded by ORF EVM158, were enumerated by MHC class I-tetramer staining.