Nainisha Shah, Emile Dufourcq-Lopez, Georgia Afonso and Pascale Louis-Plence*

University of Montpellier; IRMB Inserm U1183, Montpellier.

Regulatory T (Treg) cells play a crucial role in immunological tolerance and homeostasis, the loss or functional deficiency of Tregs is one of the proposed causes of rheumatoid arthritis. TNF has been associated with a wide variety of inflammatory conditions, and its significance in the pathogenesis of rheumatoid arthritis has been the primary reason for the use of anti-TNF antibodies in the treatment of the disease. However, the role of TNF in the suppressive ability of regulatory T cells is still controversial. In this study, we cell sorted naive and effector Treg cells based on their phenotypes, CD4⁺CD25⁺CD127^-CD45RA⁺ and CD4⁺CD25⁺CD127^- CD45RA^-, respectively, and successfully evaluated the impact of TNF on proliferation, phenotype, and in vitro suppression. Both Treg populations display high expression of FoxP3 and HELIOS, which is maintained post-expansion in the presence of TNF. These expanded cell populations were proliferative and exhibited an increase in HLA-DR, CD39, and CTLA-4, suggesting an activated phenotype. In vitro suppression by both Treg cells expanded with or without TNF, when co-cultured with activated CD4⁺CD25⁻ T cells expanded with or without TNF showed variable levels of suppression. TNF-treated CD4⁺CD25^- T cells were more resistant to Treg mediated suppression. Our results suggest that, rather than rendering Tregs ineffective, TNF affects the functionality of the CD4⁺CD25^- cell population that becomes resistant to Tregs. Therefore, the effect of TNF on human CD4⁺CD25^- T cells should also be considered when looking at Treg-mediated suppression.

Keywords - regulatory T cells, Foxp3, in vitro suppression, TNF, CD4⁺CD25^-