Cytokine Diversity in the Th1-Dominated Human Anti- Influenza Response Caused by Variable Cytokine Expression by Th1 Cells, and a Minor Population of

Within overall Th1-like human memory T cell responses, individual T cells may express only some of the characteristic Th1 cytokines when reactivated. In the Th1-oriented memory response to influenza, we have tested the contributions of two potential mechanisms for this diversity: variable expression of cytokines by a uniform population during activation, or different stable subsets that consistently expressed subsets of the Th1 cytokine pattern. To test for short-term variability, in vitro-stimulated influenza-specific human memory CD4+ T cells were sorted according to IL-2 and IFNc expression, cultured briefly in vitro, and cytokine patterns measured after restimulation. Cells that were initially IFNc+ and either IL-2+ or IL-2-converged rapidly, containing similar proportions of IL-2-IFNc+ and IL-2+IFNc+ cells after culture and restimulation. Both phenotypes expressed Tbet, and similar patterns of mRNA. Thus variability of IL-2 expression in IFNc+ cells appeared to be regulated more by short-term variability than by stable differentiated subsets. In contrast, heterogeneous expression of IFNc in IL-2+ influenza-specific T cells appeared to be due partly to stable T cell subsets. After sorting, culture and restimulation, influenza-specific IL-2+IFNc- and IL-2+IFNc+ cells maintained significantly biased ratios of IFNc+ and IFNc- cells. IL-2+IFNc-cells included both Tbetlo and Tbethi cells, and showed more mRNA expression differences with either of the IFNc+ populations. To test whether IL-2+IFNc-Tbetlo cells were Thpp cells (primed but uncommitted memory cells, predominant in responses to protein vaccines), influenza-specific IL-2+IFNc- and IL-2+IFNc+ T cells were sorted and cultured in Th1- or Th2