Gina J. Walter

Interleukin-17+CD8+ T Cells Are Enriched in the Joints of Patients With Psoriatic Arthritis and Correlate With Disease Activity and Joint Damage Progression

Psoriatic arthritis (PsA) is associated with HLA class I genes, in contrast to the association with HLA class II in rheumatoid arthritis (RA). Since IL‐17+ cells are considered important mediators of synovial inflammation, we sought to determine whether IL‐17–producing CD8+ T cells may be found in the joints of patients with PsA and whether these cells might contribute to the disease process.

CD161 expression characterizes a subpopulation of human regulatory T cells that produces IL‐17 in a STAT3‐dependent manner

Treg cells are critical for the prevention of autoimmune diseases and are thus prime candidates for cell‐based clinical therapy. However, human Treg cells are “plastic”, and are able to produce IL‐17 under inflammatory conditions. Here, we identify and characterize the human Treg subpopulation that can be induced to produce IL‐17 and identify its mechanisms. We confirm that a subpopulation of human Treg cells produces IL‐17 in vitro when activated in the presence of IL‐1β, but not IL‐6. “IL‐17 potential” is restricted to population III (CD4+CD25hiCD127loCD45RA−) Treg cells expressing the natural killer cell marker CD161. We show that these cells are functionally as suppressive and have similar phenotypic/molecular characteristics to other subpopulations of Treg cells and retain their suppressive function following IL‐17 induction. Importantly, we find that IL‐17 production is STAT3 dependent, with Treg cells from patients with STAT3 mutations unable to make IL‐17. Finally, we show that CD161+ population III Treg cells accumulate in inflamed joints of patients with inflammatory arthritis and are the predominant IL‐17‐producing Treg‐cell population at these sites. As IL‐17 production from this Treg‐cell subpopulation is not accompanied by a loss of regulatory function, in the context of cell therapy, exclusion of these cells from the cell product may not be necessary.

TNF-α blockade induces IL-10 expression in human CD4+ T cells

IL-17+ CD4+ T (Th17) cells contribute to the pathogenesis of several human inflammatory diseases. Here we demonstrate that TNF-inhibitor (TNFi) drugs induce the anti-inflammatory cytokine IL-10 in CD4+ T cells including IL-17+ CD4+ T cells. TNFi-mediated induction of IL-10 in IL-17+ CD4+ T cells is Treg/Foxp3 independent, requires IL-10 and is overcome by IL-1β. TNFi-exposed IL-17+ CD4+ T cells are molecularly and functionally distinct, with a unique gene signature characterised by expression of IL10 and IKZF3 (encoding Aiolos). We show that Aiolos binds conserved regions in the IL10 locus in IL-17+ CD4+ T cells. Furthermore, IKZF3 and IL10 expression levels correlate in primary CD4+ T cells and Aiolos overexpression is sufficient to drive IL10 in these cells. Our data demonstrate that TNF-α blockade induces IL-10 in CD4+ T cells including Th17 cells and suggest a role for the transcription factor Aiolos in the regulation of IL-10 in CD4+ T cells.

CD4+CD25+ regulatory T cells in systemic sclerosis and other rheumatic diseases.

Systemic sclerosis (SSc) is a generalized connective tissue disorder, characterized by a wide spectrum of microvascular and immunological abnormalities, leading to a progressive thickening and fibrosis of the skin and other organs, such as the lungs, GI tract, heart and kidneys. SSc is thought to be an autoimmune disease owing to the presence of high affinity antibodies and possible clinical overlap with other autoimmune diseases such as systemic lupus erythematosus and rheumatoid arthritis. Autoimmune diseases arise because of a breakdown in immunological self tolerance. Self tolerance is maintained via multiple regulatory mechanisms within the immune system, including the thymic deletion of self-reactive T cells and mechanisms of peripheral tolerance. In recent years, the presence of CD4+CD25+FOXP3+ Tregs has been identified as a major mechanism of peripheral tolerance, and accumulating evidence indicates that alterations in Treg frequencies and/or function may contribute to autoimmune diseases. Here, we will review recent data on the percentage, function and phenotype of CD4+CD25+ Tregs in rheumatic disease, and discuss how recent developments may guide research in this area in SSc.

FAS/FAS-L dependent killing of activated human monocytes and macrophages by CD4+CD25-responder T cells, but not CD4+CD25+regulatory T cells

Conclusive resolution of an immune response is critical for the prevention of autoimmunity and chronic inflammation. We report that following co-culture with autologous CD4+CD25- responder T cells, human CD14+ monocytes and monocyte-derived macrophages become activated but also significantly more prone to apoptosis than monocytes/macrophages cultured alone. In contrast, in the presence of CD4+CD25+ regulatory T cells (Tregs), monocytes and macrophages survive whilst adopting an anti-inflammatory phenotype. The induction of monocyte death requires responder T cell activation and cell-contact between responder T cells and monocytes. We demonstrate a critical role for FAS/FAS-L ligation in responder T cell-induced monocyte killing since responder T cells, but not Tregs, upregulate FAS-ligand (FAS-L) mRNA, and induce FAS expression on monocytes. Furthermore, responder T cell-induced monocyte apoptosis is blocked by neutralising FAS/FAS-L interaction, and is not observed when monocytes from an autoimmune lymphoproliferative syndrome (ALPS) patient with complete FAS-deficiency are used as target cells. Finally, we show that responder T cell-induced killing of monocytes is impaired in patients with active rheumatoid arthritis (RA). Our data suggest that resolution of inflammation in the course of a healthy immune response is aided by the unperturbed killing of monocytes with inflammatory potential by responder T cells and the induction of longer-lived, Treg-induced, anti-inflammatory monocytes.

Periodontitis-associated pathogens P. gingivalis and A. actinomycetemcomitans activate human CD14(+) monocytes leading to enhanced Th17/IL-17 responses.

The Th17/IL‐17 pathway is implicated in the pathogenesis of periodontitis (PD), however the mechanisms are not fully understood. We investigated the mechanism by which the periodontal pathogens Porphyromonas gingivalis (Pg) and Aggregatibacter actinomycetemcomitans (Aa) promote a Th17/IL‐17 response in vitro, and studied IL‐17+ CD4+ T‐cell frequencies in gingival tissue and peripheral blood from patients with PD versus periodontally healthy controls. Addition of Pg or Aa to monocyte/CD4+ T‐cell co‐cultures promoted a Th17/IL‐17 response in vitro in a dose‐ and time‐dependent manner. Pg or Aa stimulation of monocytes resulted in increased CD40, CD54 and HLA‐DR expression, and enhanced TNF‐α, IL‐1β, IL‐6 and IL‐23 production. Mechanistically, IL‐17 production in Pg‐stimulated co‐cultures was partially dependent on IL‐1β, IL‐23 and TLR2/TLR4 signalling. Increased frequencies of IL‐17+ cells were observed in gingival tissue from patients with PD compared to healthy subjects. No differences were observed in IL‐17+ CD4+ T‐cell frequencies in peripheral blood. In vitro, Pg induced significantly higher IL‐17 production in anti‐CD3 mAb‐stimulated monocyte/CD4+ T‐cell co‐cultures from patients with PD compared to healthy controls. Our data suggest that periodontal pathogens can activate monocytes, resulting in increased IL‐17 production by human CD4+ T cells, a process that appears enhanced in patients with PD.

Phenotypic, Functional, and Gene Expression Profiling of Peripheral CD45RA+ and CD45RO+ CD4+CD25+CD127(low) Treg Cells in Patients With Chronic Rheumatoid Arthritis.

Conflicting evidence exists regarding the suppressive capacity of Treg cells in the peripheral blood (PB) of patients with rheumatoid arthritis (RA). The aim of this study was to determine whether Treg cells are intrinsically defective in RA.

Phenotypic, functional and gene expression profiling of peripheral CD45RA+ and CD45RO+ CD4+CD25+CD127low regulatory T cells in rheumatoid arthritis

Conflicting evidence exists regarding the suppressive capacity of Treg cells in the peripheral blood (PB) of patients with rheumatoid arthritis (RA). The aim of this study was to determine whether Treg cells are intrinsically defective in RA.

Interaction with activated monocytes enhances cytokine expression and suppressive activity of human CD4+CD45RO+CD25+CD127low regulatory T cells

Despite the high frequency of CD4+ T cells with a regulatory phenotype (CD25+CD127lowFoxP3+) in the joints of patients with rheumatoid arthritis (RA), inflammation persists. Regulatory T cells (Tregs) can be converted into pro-inflammatory IL-17-producing cells by inflammatory mediators, particularly IL-1β.

TNF-inhibitor drugs regulate human pathogenic Th17 cells through induction of IL-10

Results Ex vivo analysis of patients with RA on TNFi therapy revealed an enrichment of Th17 cells in peripheral blood compared to those on disease-modifying anti-rheumatic drugs or healthy controls. However, we also found an increase in IL-10-producing CD4+ T-cells. The enrichment in IL-17+ and IL-10+ CD4+ T-cells, including IL17+IL-10+ co-expressing CD4+ T-cells, was recapitulated in vitro by the addition of TNFi drugs (adalimumab, infliximab, etanercept, and certolizumab) to human monocyte/CD4+ T-cell co-cultures. IL-10 induction was independent of FcgR binding, IL-10 and CD4+CD25+ Tregs. TNFi-induced Th17 cells were functionally distinct as shown by an ability to modulate CD14+ monocytes in an IL-10-dependent manner. We report the identification of a transcription factor that is strongly associated with IL-10 expression in TNFi-induced IL-17+ CD4+ T-cells, and show that overexpression of this transcription factor drives IL-10 expression in primary CD4+ T-cells.