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Maintenance of regulatory T cells CD4 + CD25 high FOXP3 + (Treg) stability is vital for proper Treg function and controlling the immune equilibrium. Treg cells are heterogeneous and can reveal plasticity, exemplified by their potential to express IL-17A. TNFα-TNFR2 signaling controls IL-17A expression in conventional T cells via the anti-inflammatory ubiquitin-editing and kinase activity regulating enzyme TNFAIP3/ A20 (tumor necrosis factor-alpha-induced protein 3). To obtain a molecular understanding of TNFα signaling on IL-17 expression in the human effector ( eff Treg, CD25 high CD45RA - ) Treg subset, we here studied the kinome activity regulation by TNFα signaling. Using FACS-sorted naïve ( naïve Treg, CD25 high CD45RA + ) and eff Treg subsets, we demonstrated a reciprocal relationship between TNFα and IL-17A expression; eff Treg (TNFα low /IL-17A high ) and naïve Treg (TNFα high /IL-17A low ). In eff Treg, TNFα-TNFR2 signaling prevented IL-17A expression, whereas inhibition of TNFα signaling by clinically applied anti-TNF antibodies led to increased IL-17A expression. Inhibition of TNFα signaling led to reduced TNFAIP3 expression, which, by using siRNA inhibition of TNFAIP3 , appeared causally linked to increased IL-17A expression in eff Treg. Kinome activity screening of CD3/CD28-activated eff Treg revealed that anti-TNF-mediated neutralization led to increased kinase activity. STRING association analysis revealed that the TNF suppression eff Treg kinase activity network was strongly associated with kinases involved in TCR, JAK, MAPK, and PKC pathway signaling. Small-molecule-based inhibition of TCR and JAK pathways prevented the IL-17 expression in eff Treg. Together, these findings stress the importance of TNF-TNFR2 in regulating the kinase architecture of antigen-activated eff Treg and controlling IL-17 expression of the human Treg. These findings might be relevant for optimizing anti-TNF-based therapy and may aid in preventing Treg plasticity in case of Treg-based cell therapy., (Copyright © 2020 Urbano, He, Heeswijk, Filho, Tijssen, Smeets, Joosten and Koenen.)

Background: Anti-TNF inhibitors successfully improve the quality of life of patients with inflammatory disease. Unfortunately, not all patients respond to anti-TNF therapy, and some patients show paradoxical immune side effects, which are poorly understood. Surprisingly, anti-TNF agents were shown to promote IL-17A production with as yet unknown clinical implications., Objective: We sought to investigate the molecular mechanism underlying anti-TNF-driven IL-17A expression and the clinical implications of this phenomenon., Methods: Fluorescence-activated cell sorting, RNA sequencing, quantitative real-time PCR, Western blotting, small interfering RNA interference, and kinase inhibitors were used to study the molecular mechanisms in isolated human CD4 + T cells from healthy donors. The clinical implication was studied in blood samples of patients with inflammatory bowel disease (IBD) receiving anti-TNF therapy., Results: Here we show that anti-TNF treatment results in inhibition of the anti-inflammatory molecule TNF-α-induced protein 3 (TNFAIP3)/A20 in memory CD4 + T cells. We found an inverse relationship between TNFAIP3/A20 expression levels and IL-17A production. Inhibition of TNFAIP3/A20 promotes kinase activity of p38 mitogen-activated protein kinase and protein kinase C, which drives IL-17A expression. Regulation of TNFAIP3/A20 expression and cognate IL-17A production in T cells are specifically mediated through TNF receptor 2 signaling. Ex vivo, in patients with IBD treated with anti-TNF, we found further evidence for an inverse relationship between TNFAIP3/A20 expression levels and IL-17A-producing T cells., Conclusion: Anti-TNF treatment interferes in the TNFAIP3/A20-mediated anti-inflammatory feedback loop in CD4 + T cells and promotes kinase activity. This puts TNFAIP3/A20, combined with IL-17A expression, on the map as a potential tool for predicting therapy responsiveness or side effects of anti-TNF therapy. Moreover, it provides novel targets related to TNFAIP3/A20 activity for superior therapeutic regimens in patients with IBD., (Copyright © 2017 American Academy of Allergy, Asthma & Immunology. Published by Elsevier Inc. All rights reserved.)

Clinical trials successfully using antibodies targeting IL-17 in psoriasis support the importance of IL-17 in the pathophysiology of this disease. However, there is a debate concerning the source and dynamics of IL-17 production in inflamed skin. Here we characterized IL-17-producing immune cells over time, using two established in vivo models of human skin inflammation that share many histological features with psoriasis, i.e., leukotriene B4 application and tape-stripping. Both treatments revealed a clear influx of neutrophils and T cells. Staining for IL-17 revealed that the majority of IL-17 was expressed by neutrophils and mast cells, in both models. Neutrophils, but not mast cells, coexpressed the IL-17-associated transcription factor RORγt and were able to form extracellular traps. While the presence of mast cells remained steady during the skin inflammatory process, the presence of neutrophils was clearly dynamic in time. Therefore, it is attractive to hypothesize that IL-17+/RORγt+ neutrophils contribute to human skin inflammation in vivo and possibly to the pathogenesis of skin diseases such as psoriasis. Surprisingly, T cells represented a minority of the IL-17-expressing cell population. These observations challenge the classical opinion that IL-17 is predominantly associated with T cells in skin inflammation.

Regulatory T-cells (Treg) are crucial for immune homeostasis and prevention of immune pathology. Yet, Treg may lose Foxp3 and start secreting IL-17, dependent on environmental cues. Our previous data revealed that Treg from severe psoriasis patients are particularly prone to such conversion. The question of how to maintain Treg stability in the context of inflammation awaits immediate resolution. The pan-protein kinase C (PKC) inhibitor sotrastaurin has shown efficacy in clinical trials of psoriasis. Here, we show that sotrastaurin inhibited effector T-cell responses, whereas the regulatory response was enhanced. Sotrastaurin prevented TCR/CD28-induced T-cell activation and pro-inflammatory cytokine production, but preserved a stable Treg phenotype as evidenced by maintenance of suppressive capacity, high Foxp3 and CD25 expression, and lack of IL-17A and IFNγ production. Moreover, in both circulating and dermal psoriatic Treg, prone to rapid induction of IL-17, sotrastaurin enhanced Foxp3 expression and prevented IL-17A and IFNγ production even when stimulated in the presence of the helper T 17-enhancing cytokines IL-1β or IL-23. Thus, pharmacological inhibition of PKC may serve as a powerful tool to concurrently inhibit effector T cells and to facilitate Treg, thereby showing therapeutic potential for the treatment of psoriasis.