To distinguish the relative contributions of short-term versus pre-determined variability of Th1 cytokine expression in influenza responses, we used a combination of sorting, restimulation, evaluation of Tbet expression, RNAseq and in vitro differentiation to show that both mechanisms appeared to operate in influenza-specific or polyclonally-activated human memory CD4 T cells. This evidence concerns the gene TBX21 and influenza.