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 bona fide Tr1 cell protein and mRNA signatures. Kinetic transcriptional analysis revealed that the Tr1 cell module was transient and preceded by a burst of Ifng transcription in CD4+ T-cells. Neutralisation of IFNγ reduced Tr1 cell frequency and strong TCR signalling markers, which was correlated with reduced macrophage activation. Antibody depletion experiments inferred that T-cells – but not NK cells – provided the relevant source of IFNγ. Additionally, we show that blocking IL-27 in combination with IFNγ neutralisation additively reduced Tr1 cell frequency in vivo. These findings reveal that during strong tolerogenic TCR signalling IFN-γ has a non-redundant regulatory role in augmenting the differentiation of Tr1 cells in vivo.