Introduction In RA, Tregs fail to control chronic inflammation. TNF-α is involved in inhibition of Tregs differentiation and activation but the respective roles of its two receptors is unclear.
We aimed to establish the role of TNFR2 on Tregs in control of inflammation by studying: 1) the action of TNF on Treg function in the presence and absence of TNFR2 in vitro and 2) in a model of skin inflammation in TNFR2KO mice, 3) the evolution of TNFR2-expressing Tregs from RA patients during anti-TNF-treatment.
Methods: Mice deficient in the TNFR2 gene (TNFR2KO) and CRE-FoxP3-TNFR2 lox/lox mice were used. Cell phenotype was evaluated by FACS. Tregs stability was evaluated by analyzing methylation status of 9 CpG motifs of the Foxp3-locus (bisulfite sequencing of CD4+CD25+ purified cells). Skin inflammation was induced by an imiquimod-containing ointment. Peripheral blood Tregs were characterized before and after 3 months of anti–TNF treatment in 12 RA-patients and in 19 patients with axial spondylaorthritis (AxSpA).
Results: In vitro, TNF-α enhanced Foxp3 maintenance through TNFR2 signaling in cultured Tregs. In vivo, TNFR2-negative-Treg cells from both TNFR2KO and CRE-FoxP3-TNFR2 lox/lox mice, had lower spontaneous suppressive capacities (lower inhibition of effector T cell proliferation and IFN-g production). FoxP3 methylation was higher in Tregs from TNFR2KO mice than wt mice. This suggested that TNFR2 expression confers higher stability to Tregs.
TNFR2KO mice had enhanced skin-inflammation and decreased Tregs and CD39+ Tregs frequencies in lymph nodes. In RA patients responding to anti-TNF treatment, an increase in TNFR2-expressing-Tregs frequencies was evident at 3 months of treatment vs. the baseline. Conversely, no variation was observed in AxSpA patients
Conclusion: TNFR2 signaling on Tregs may play a major role in controlling inflammation and can be activated both by TNF-α and anti-TNF treatment. Further studies to dissect TNFR2 dependent pathways on Tregs are warranted.