Effector CD4+ and CD8+ T cell responses in BALB/c mice immunized with PEI/pci-S complexes. Multi-intracellular cytokine staining for IL-17, IFN-γ, TNF-α and IL-2 was performed on (A) CD4+ and (B) CD8+ T cells after in vitro re-stimulation with SARS peptide. SARS S-specific CD4+ T cells from lung were recovered on day 6 after the last immunization. ND indicates not detectable. Data were expressed as the mean value of mean fluorescence intensity ± SEM. Significant differences compared with pci-S group were expressed as *P < 0.01. (C) The results showed representative example of flow cytometry analysis.