CTL priming in B-cell–deficient mice. Four CTL peptides of different MHC class I binding affinity were used as immunogens in B-cell–deficient mice and compared with wild-type C57BL/6 mice. Open symbols represent the cytolytic response in B-cell–deficient mice, and solid symbols represent responses in wild-type mice in all panels. Two experiments have been averaged (SD ≤ 6% lysis for all E/T ratios). (A) Specific lysis measured by ⁵¹Cr release using as immunogens 2 immunodominant and Th cell–independent viral sequences emulsified in IFA. (B) Immunization with the same CTL epitopes where T-cell help is provided by co-injection with a helper peptide, the sequence derived from the hepatitis B virus (HBV) HBc 128-140. (C) CTL induction following priming with 2 subdominant Th-dependent peptides co-injected with Th (HBc 128-140 for the CTL determinant LCMV NP 205-212 and OVA 323-336 for the CTL determinant OVA 55-62). (D) Representative ex vivo IFNγ measurement by the ELISPOT assay in response to the T helper–independent VSV NP 52-59 and T helper–dependent OVA 55-62 peptides, co-injected with the helper OVA 323-336 determinant (SD ≤ 2%). (E) Ex vivo IFNγ measurement by ELISPOT assay in CD4⁺ T-cell–depleted spleen cells in response to the whole OVA protein used as immunogen in CFA: representative CTL responses in 2 wild-type C57BL/6 mice and 2 B-cell–deficient mice from the same experiment.