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

Strong T-cell receptor (TCR) and IL-27 signalling influence type-1 regulatory (Tr1) T-cell development, but whether other signals determine their differentiation is unclear. Utilising 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 Il10⁺ 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 Ifng transcription in other CD4⁺ T cells. Changes in Tr1 cell frequency correlated with altered macrophage activation, while neutralisation of IFN_γ reduced Tr1 cell frequency and the TCR signal strength markers Nur77, ICOS and OX40. Antibody depletion experiments inferred that the relevant source of IFN_γ was not NK cell derived. Additionally, blocking IL-27 in combination with IFN_γ neutralisation additively reduced Tr1 cell frequency in vivo. These findings reveal that IFN_-γ has a non-redundant role in augmenting Tr1 cell differentiation in vivo.