Compromised CD4+ CD25high regulatory T‐cell function in patients with relapsing‐remitting multiple sclerosis is correlated with a reduced frequency of FOXP3‐positive cells and reduced FOXP3 expression at the single‐cell level

Abstract

CD4⁺ CD25^high regulatory T cells (Tregs) of patients with relapsing-remitting (RR) multiple sclerosis (MS), in contrast to those of patients with secondary progressive (SP) MS, show a reduced suppressive function. In this study, we analysed forkhead box P3 (FOXP3) at the single-cell level in MS patients and controls (healthy individuals and patients with other neurological diseases) by means of intracellular flow cytometry. Our data revealed a reduced number of peripheral blood CD4⁺ CD25^high FOXP3⁺ T cells and lower FOXP3 protein expression per cell in RR-MS patients than in SP-MS patients and control individuals, which was correlated with the suppressive capacity of Tregs in these patients. Interestingly, interferon (IFN)-β-treated RR-MS patients showed restored numbers of FOXP3⁺ Tregs. Furthermore, a higher percentage of CD4⁺ CD25^high FOXP3⁺ Tregs in RR-MS patients, as compared with controls and SP-MS patients, expressed CD103 and CD49d, adhesion molecules involved in T-cell recruitment towards inflamed tissues. This was consistent with a significantly increased number of CD27⁺ CD25^high CD4⁺ T cells in the cerebrospinal fluid (CSF), as compared with peripheral blood, in RR-MS patients. Taken together, these data show aberrant FOXP3 expression at the single-cell level correlated with Treg dysfunction in RR-MS patients. Our results also suggest that Tregs accumulate in the CSF of RR-MS patients, in an attempt to down-regulate local inflammation in the central nervous system.