Both wild-type and FasL KO mice have comparable luciferase-specific CD4⁺ T-cell responses after plasmid DNA-Luc inoculation, but only adoptively transferred primed wild-type CD4⁺ T cells damp luciferase expression. (A) CD4⁺ T-cell activation in wild-type and FasL KO mice that were inoculated with plasmid DNA-Luc. Splenocytes from these mice were stimulated with a pool of luciferase peptides for 6 hours, and CD4⁺ T-cell responses were measured by intracellular anti-IL-2 antibody staining and flow cytometric analysis. (B) Luciferase expression in Rag KO mice without adoptive transfer (Rag KO) and Rag KO mice adoptively transferred with CD4⁺ T cells obtained from FasL KO (Rag CD4-FasL KO) mice. (C) Luciferase expression in Rag KO mice without adoptive transfer (Rag KO) and Rag mice adoptively transferred with CD4⁺ T cells obtained from wild-type (Rag CD4-wild-type) mice. For adoptive transfer studies, CD4⁺ T cells from wild-type and FasL KO mice were obtained each 14 days after plasmid DNA inoculation, and 10⁷ CD4⁺ T cells were adoptively transferred into Rag KO mice. The mice were then inoculated with the plasmid DNA-Luc vaccine construct, and luciferase expression in vivo was monitored by IVIS imaging. The line graphs represent mean values; error bars represent SEM. Statistically significant differences at specific times were determined by the Mann-Whitney test. *Significant difference (P < .05).