Figure 3. CD4 ⁺ T cells do not require CD27 expression to provide help.

Groups of 4 CD4 ^−/− mice received 5×10⁴ wild-type or CD27 ^−/− OT-II cells. One day later, the mice were challenged with 5×10⁶ Act-mOVA/K^{b −/−} splenocytes. After 7 days, the primary endogenous OVA_{257 – 264}/K^b-specific response was measured by MHC/peptide tetramer analysis and intracellular cytokine staining for IFN-γ. Some groups were re-challenged 30 days later with 5×10⁶ pfu Vacc-OVA and the secondary response measured 5 days later. (a) The percentage of IFNγ ⁺ OVA_{257 – 264}/K^b-specific CD8 ⁺ among total splenocytes spleen during primary (day 7), memory (day 30) and secondary response (day 30 + 5 days post challenge). (b) The absolute number of IFNγ ⁺ OVA_{257 – 264}/K^b-specific CTL in the spleen, and (c) the OVA OVA_{257 – 264}/K^b-specific/K^b tetramer response by the CTL at these same time points. Error bars represent the s.d. of three mice. Significant difference was calculated by an unpaired two-tailed t-test. *P-value < 0.05; **P < 0.005; ***P < 0.0005. The figures show representative experiments that were repeated at least twice with similar results.