IKK2 controls the inflammatory potential of tissue-resident regulatory T cells in a murine gain of function model

Loss-of-function mutations have provided crucial insights into the immunoregulatory actions of Foxp3+ regulatory T cells (Tregs). By contrast, we know very little about the consequences of defects that amplify aspects of Treg function or differentiation. Here we show that mice heterozygous for an Ikbkb gain-of-function mutation develop psoriasis. Doubling the gene dose ( Ikbkb GoF/GoF ) results in dactylitis, spondylitis, and characteristic nail changes, which are features of psoriatic arthritis. Ikbkb GoF mice exhibit a selective expansion of Foxp3 + CD25+ Tregs of which a subset express IL-17. These modified Tregs are enriched in both inflamed tissues, blood and spleen, and their transfer is sufficient to induce disease without conventional T cells. Single-cell transcriptional and phenotyping analyses of isolated Tregs reveal expansion of non-lymphoid tissue (tissue-resident) Tregs expressing Th17-related genes, Helios, tissue-resident markers including CD103 and CD69, and a prominent NF-κB transcriptome. Thus, IKK2 regulates tissue-resident Treg differentiation, and overactivity drives dose-dependent skin and systemic inflammation. Loss of function mutation studies has provided insights into regulatory T-cell biology. Here Cardinez et al explore the effects of a murine Ikbkb (IKK2) gain of function model and show IKK2 activity results in the expansion of regulatory T cells with partial effector function and suggest an IKK2 dose-dependent relation between psoriatic immunopathology and psoriatic arthritis.