Figure 7. 2° CD4 T cell effector number and function are reduced in the absence of IL-6.

HNT memory cells, 1×10⁶, were transferred to naïve WT BALB/c subsequently infected with 2,500 EID₅₀ A/PR8 and treated with 0.5mg of isotype or IL-6 neutralizing Ab on days 0, 2, 4, and 6 dpi. Donor cells were enumerated at 7 dpi (a). Dual IFN-γ⁺/IL-2⁺ cytokine producing cells (b) and mean fluorescence intensity of IFN-γ signal (c) was assessed at 7 dpi by ICCS (n=4 mice/group; representative of 3 similar experiments). Viral titers (d) were determined on 7 dpi in mice receiving donor HNT memory cells followed by 2,500 EID₅₀ A/PR8 challenge (n=4 mice/group; one of two experiments). WT C57Bl/6 mice were primed with A/Alaska, challenged with A/PR8 as described in Figure 3, and mice treated with isotype or IL-6 neutralizing Ab as described above. On 5dpi, NP_311–325 tetramer⁺ CD4 T cells detected in the lung (e) were assessed for dual IFN-γ⁺/IL-2⁺ cytokine producing cells. The frequency (f and g) and number (h) is shown (n=4 mice/group; one of 2 similar experiments).