CD4 and infection: By comparing the median fluorescence intensity (MFI) obtained by FCM for the investigated cytokines (IFN-γ, TNF-α, IL-2) among single-, double- and triple-cytokine-producing CD4+ T cells isolated from week 2 after primary infection onwards, we found higher quantities of IFN-γ and TNF-α in triple- and double-producers (Figures 5A and B and Additional file 6).