Interferon-γ and IL-27 positively regulate type 1 regulatory T cell development during adaptive tolerance

Strong T cell receptor (TCR) and interleukin (IL)-27 signaling influence type 1 regulatory (Tr1) T cell development, but whether other signals determine their differentiation is unclear. Utilizing Tg4 TCR transgenic mice, we established a model for rapid Tr1 cell induction. A single high dose of [4Y]-MBP peptide drove the differentiation of <i>Il10</i> ⁺ T cells with Tr1 cell mRNA and protein signatures. Kinetic transcriptional and phenotypic analyses revealed that the Tr1 cell module was transient and preceded by <i>Ifng</i> transcription in other CD4⁺ T cells. Changes in Tr1 cell frequency correlated with altered macrophage activation, while neutralization of interferon (IFN)γ reduced Tr1 cell frequency and the TCR signal strength markers Nur77, inducible T cell costimulator (ICOS), and OX40. Antibody depletion experiments inferred that the relevant source of IFNγ was not natural killer (NK) cell derived. Additionally, blocking IL-27 in combination with IFNγ neutralization additively reduced Tr1 cell frequency <i>in vivo</i>. These findings reveal that IFNγ has a non-redundant role in augmenting Tr1 cell differentiation <i>in vivo</i>.