Mitigated suppressive function of regulatory T cells (Treg) upon Th17-inducing cytokines in oligo- and polyarticular Juvenile Idiopathic Arthritis (JIA) patients

Abstract

Background The plasticity of T helper-17 (Th17) and regulatory T (Treg) cells may be a clue to pathogenesis of Juvenile Idiopathic Arthritis (JIA). It is still unclear, whether targeted suppression of Interleukin (IL)-17 is able to influence regulatory function of Treg to control pro-inflammatory effectors in JIA. This study aimed to assess the effect of a Th17-stimulating cytokine environment and of IL-17A-inhibition on phenotype plasticity and suppressive function of Treg derived from JIA patients. Methods Th17 and Treg characteristics of CD4+ helper T cells were investigated in blood samples of JIA patients with oligo- and polyarticular pattern and healthy controls (HC). Isolated CD4+CD25+CD127− cells defined as Treg were cultivated with Th17-inducing cytokine environment as well as with IL-17A-inhibitors and analyzed for plasticity of phenotype by flow cytometry. Furthermore, inhibitory function of Treg on autologous effectors after cultivation with these stimuli was determined by suppression assays. Results Our findings demonstrated significantly elevated proportions of Th17 and Th17-like Treg in JIA compared to HC. After incubation with Th17-inducing stimuli, increased FoxP3 expression in separated Treg in JIA and an impaired suppressive capacity in JIA and HC were found. Blockade of IL-17A resulted in adjustment of FoxP3-expression in JIA to proportions found in controls and in regular suppressive function. Conclusions Our results demonstrate an induction of FoxP3 expressing Treg by Th17-inducing cytokines with concomitant mitigated suppressive function. In contrast, specific IL-17A blockade maintains suppressive Treg function and adjusted FoxP3-expression in JIA to levels found in controls. These findings may help to provide experimental evidence for the successful clinical use of IL-17A inhibition in JIA patients.

The immune landscape of the inflamed joint defined by spectral flow cytometry

“…We found high levels of TNFR2 on over 60% of SF Treg clusters and the ligand TNF-a is increased in the inflamed joint (4), thus it remains to be seen which metabolic pathway Tregs utilise in SF and how this alters their functionality. In conventional T cells, TNFR2 expression and subsequent glutamine catabolism and glycolysis have been linked to pro-inflammatory actions and impact on the Th17-Treg balance (51,90,91), a key imbalance implicated in the pathogenesis of JIA (19,84). Moreover, TNFR2 expression on CD4+ conventional T cells might contribute to resistance to Treg suppression (49,50).…”

“…Alternatively, high levels of iron have been reported within synovial fluid of inflamed joints in RA (82), where iron overload may impair differentiation and function of Th1 and Th17, and death of Tregs through increased reactive oxygen species (79, 83). Th1, Th17 and Treg balance has been previously implicated in JIA pathogenesis (19, 84, 85). Similarly, elevated CD71 was found to alter T cell function, promoting a pro-inflammatory phenotype in lupus and idiopathic inflammatory myopathies (56, 86).…”

“…In conventional T cells, TNFR2 expression and subsequent glutamine catabolism and glycolysis have been linked to pro-inflammatory actions and impact on the Th17-Treg balance (51, 90, 91), a key imbalance implicated in the pathogenesis of JIA (19, 84). Moreover, TNFR2 expression on CD4+ conventional T cells might contribute to resistance to Treg suppression (49, 50).…”

“…SF Tregs retain hypomethylation of the TSDR (Treg specific demethylated region), showing commitment to the Treg fate (13), and decreased numbers might associate with disease severity (12). However, several genetic risk alleles in JIA are in loci associated with Treg function (7), SF Tregs can exhibit a proinflammatory effector phenotype, loss of IL-2 sensitivity and their in vitro suppressive capacity has been questioned in some studies (5,(12)(13)(14)(15)(16)(17)(18)(19)(20). Thus, the effects of the pro-inflammatory microenvironment on SF immune cells, including Tregs, need to be further assessed to understand their role in ongoing disease.…”

Treg fitness as a biomarker for disease activity in Juvenile Idiopathic Arthritis

“…Interestingly, SF Tregs retain hypomethylation of the TSDR (Treg specific demethylated region), showing commitment to the Treg fate (21) and increased numbers may associate with less extensive disease (22). However, several genetic risk alleles in JIA are in loci associated with Treg function (16), with synovial Tregs suggested to exhibit a pro-inflammatory effector phenotype, loss of IL-2 sensitivity and questioned in vitro suppressive capacity (17,18,21,(23)(24)(25)(26)(27). Investigations into altered Treg phenotype in the blood between inactive and active JIA are more limited in non-systemic JIA.…”