Senescence or biological aging impacts a vast variety of molecular and cellular processes. To date, it is unknown whether CD4+ Th cells display an age-dependent bias for development into specific subpopulations. In this study, we show the appearance of a distinct CD4+ T cell subset expressing IL-4 at an early stage of development in infant adenoids and cord blood that is lost during aging. We identified by flow cytometric, fluorescent microscopic, immunoblot, and mass spectrometric analysis a population of CD4+ T cells that expressed an unglycosylated isoform of IL-4. This T cell subpopulation was found in neonatal but not in adult CD4+ T cells. Furthermore, we show that the mRNA of the Th2 master transcription factor GATA3 is preferentially expressed in neonatal CD4+ T cells. The Th2 phenotype of the IL-4+CD4+ T cells could be reinforced in the presence of TGF-β. Although the IL-4+CD4+ T cells most likely originate from CD31+CD4+ T recent thymic emigrants, CD31 was downregulated prior to secretion of IL-4. Notably, the secretion of IL-4 requires a so far unidentified trigger in neonatal T cells. This emphasizes that cytokine expression and secretion are differentially regulated processes. Our data support the hypothesis of an endogenously poised cytokine profile in neonates and suggest a link between cytokine production and the developmental stage of an organism. The determination of the IL-4 isoform–expressing cells in humans might allow the identification of Th2 precursor cells, which could provide novel intervention strategies directed against Th2-driven immunopathologies such as allergies.

Cytokines are critical messengers that control the differentiation of Th cells. To evaluate their impact on the fate of human naive CD4+ T cells from cord and adult blood, early T cell differentiation was monitored after T cell activation in the presence of pro- and anti-inflammatory cytokines. Interestingly, the analysis of Th cell lineage-specific molecules revealed that IL-1β on its own mediates differentiation of Th cells that secrete a wide range of proinflammatory cytokines and stably express CD69, STAT1, IFN-γ, and IL-17. Notably, our data suggest that IL-1β induces Th17 cells independent of RORC upregulation. In contrast, TGF-β that triggers RORC prevents Th17 cell development. This suppressive function of TGF-β is characterized by inhibition of STAT1, STAT3, and CD69. However, after repeated anti-CD3 and anti-CD28 stimulation, we observe that TGF-β provokes an increase in Th17 cells that presumably relies on reactivation of a default pathway by preferential inhibition of IFN-γ. Hence, our data extend the view that the principal cytokines for determining Th cell fate are IL-12 for the Th1 lineage, IL-4 for the Th2 lineage, and TGF-β in conjunction with IL-6 for the Th17 lineage. We propose that IL-1β induces a general proinflammatory Th cell precursor that, in the presence of the lineage-specifying cytokines, further differentiates into one of the specific Th cell subpopulations.