A time-gated PKA–CREB signaling circuit licenses IL-12 responsiveness and Th1 fate in CD4⁺ T cells

Naïve CD4⁺ T cells differentiate into Th1 cells upon TCR stimulation in the presence of IFN-γ and IL-12. However, the intracellular signaling networks that temporally coordinate these inputs to reinforce Th1 lineage commitment remain incompletely defined. Here, we identify protein kinase A (PKA) as a time-gated regulator of IL-12 responsiveness and Th1 differentiation. Using a conditional knockout mouse model that deletes both catalytic PKA subunits in CD4⁺ T cells, we show that PKA is dispensable for early T cell activation but is essential for the late-phase induction of IL-12 receptor β2 (Il12rb2) and STAT4. PKA-deficient CD4⁺ T cells fail to differentiate into Th1 cells in vitro and cannot induce Th1-mediated colitis in vivo. Instead, they adopt a Th2-skewed phenotype and drive eosinophilic lung inflammation and fibrosis. Mechanistically, prolonged TCR stimulation induces the expression of the peptide hormone Adrenomedullin (Adm) and its receptor component Ramp3, which activate PKA and its downstream effector CREB. Activated CREB drives Il12rb2 and Stat4 transcription, establishing a feedforward circuit that integrates signal duration with cytokine responsiveness. In the absence of PKA, this transcriptional program fails to initiate, leading to impaired IL-12 signaling and a loss of Th1 identity. These findings define a PKA–CREB signaling module that links sustained antigen stimulation to transcriptional and epigenetic commitment in CD4⁺ T cells, offering a mechanistic explanation for the temporal gating of Th1 differentiation and the prevention of Th2-driven tissue pathology.