Sequential Polarization and Imprinting of Type 1 T Helper Lymphocytes by Interferon-γ and Interleukin-12

SummaryDifferentiation of naive T lymphocytes into type I T helper (Th1) cells requires interferon-γ and interleukin-12. It is puzzling that interferon-γ induces the Th1 transcription factor T-bet, whereas interleukin-12 mediates Th1 cell lineage differentiation. We use mathematical modeling to analyze the expression kinetics of T-bet, interferon-γ, and the IL-12 receptor β2 chain (IL-12Rβ2) during Th1 cell differentiation, in the presence or absence of interleukin-12 or interferon-γ signaling. We show that interferon-γ induced initial T-bet expression, whereas IL-12Rβ2 was repressed by T cell receptor (TCR) signaling. The termination of TCR signaling permitted upregulation of IL-12Rβ2 by T-bet and interleukin-12 signaling that maintained T-bet expression. This late expression of T-bet, accompanied by the upregulation of the transcription factors Runx3 and Hlx, was required to imprint the Th cell for interferon-γ re-expression. Thus initial polarization and subsequent imprinting of Th1 cells are mediated by interlinked, sequentially acting positive feedback loops of TCR-interferon-γ-Stat1-T-bet and interleukin-12-Stat4-T-bet signaling