Cytokine Diversity in the Th1-Dominated Human Anti-Influenza Response Caused by Variable Cytokine Expression by Th1 Cells, and a Minor Population of Uncommitted IL-2+IFN gamma - Thpp Cells: e95986

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 IFN gamma expression, cultured briefly in vitro, and cytokine patterns measured after restimulation. Cells that were initially IFN gamma + and either IL-2+ or IL-2- converged rapidly, containing similar proportions of IL-2-IFN gamma + and IL-2+IFN gamma + cells after culture and restimulation. Both phenotypes expressed Tbet, and similar patterns of mRNA. Thus variability of IL-2 expression in IFN gamma + cells appeared to be regulated more by short-term variability than by stable differentiated subsets. In contrast, heterogeneous expression of IFN gamma 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+IFN gamma - and IL-2+IFN gamma + cells maintained significantly biased ratios of IFN gamma + and IFN gamma - cells. IL-2+IFN gamma - cells included both Tbetlo and Tbethi cells, and showed more mRNA expression differences with either of the IFN gamma + populations. To test whether IL-2+IFN gamma -Tbetlo cells were Thpp cells (primed but uncommitted memory cells, predominant in responses to protein vaccines), influenza-specific IL-2+IFN gamma - and IL-2+IFN gamma + T cells were sorted and cultured in Th1- or Th2-generating conditions. Both cell types yielded IFN gamma -secreting cells in Th1 conditions, but only IL-2+IFN gamma - cells were able to differentiate into IL-4-producing cells. Thus expression of IL-2 in the anti-influenza response may be regulated mainly by short term variability, whereas different T cell subsets, Th1 and Thpp, may contribute to variability in IFN gamma expression.