Figure 2.

Immunization outline and HA- and NP-specific CD4 T cell responses. (A) Six-week old BALB/c mice were electroporated intramuscularly with expression plasmids encoding for HA and NP. Additionally, the animals were either co-electroporated with an empty vector (mock) or plasmids encoding for the soluble ectodomains of PD-1 (sPD-1) or PD-L1 (sPD-L1). After two weeks, mice were sacrificed, and T cell responses analyzed. Percentage of CD4 + T cells producing IFNγ, IL-2 or TNFα after in vitro stimulation with influenza HA (B) and NP (C) T helper peptides (measured by intracellular cytokine staining). Shown are mean values with SEM (n = 5–9) and significant differences between the groups (one-way ANOVA analyses followed by Tukey’s multiple comparison test, * p < 0.05, ** p < 0.01, **** p < 0.0001).