Summary CD4+ CD25high 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+ CD25high 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+ CD25high 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+ CD25high 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.

Activated autoreactive T cells are potentially pathogenic and regulated by clonotypic networks. Experimental autoimmune diseases can be treated by inoculation with autoreactive T cells (T cell vaccination). In the present study, patients with multiple sclerosis were inoculated with irradiated myelin basic protein (MBP)-reactive T cells. T cell responses to the inoculates were induced to deplete circulating MBP-reactive T cells in the recipients. Regulatory T cell lines isolated from the recipients inhibited T cells used for vaccination. The cytotoxicity of the CD8+ T cell lines was restricted by major histocompatibility antigens. Thus, clonotypic interactions regulating autoreactive T cells in humans can be induced by T cell vaccination.

Accumulating evidence indicates an immunosuppressive role for CD4(+)CD25(+) regulatory T cells (Tregs) in autoimmune diseases. Although an impaired Treg function in patients with relapsing-remitting multiple sclerosis (RR-MS) has been reported recently, no information is available so far about Treg function in the progressive stage of the disease. In the present study, the phenotypic and functional characteristics of CD4(+)CD25(+) T cells isolated from the peripheral blood of patients with RR-MS and secondary progressive multiple sclerosis (SP-MS) were investigated. No significant quantitative or phenotypic abnormalities in CD4(+)CD25(+) T cells from RR- and SP-MS patients were detected. However, whereas a reduced suppressor function of CD4(+)CD25(+) T cells toward proliferation and interferon-gamma production of CD4(+)CD25(-) responder T cells was found in RR-MS patients, SP-MS patients showed a normal Treg function. The suppressive capacity of MS-derived CD4(+)CD25(+) T cells was correlated with disease duration but not with age, indicating that Treg function is more affected in the early phase of the disease process. Consistently with the suppressive capacity, CD4(+)CD25(+) T cells from SP-MS patients showed normal levels of FOXP3 mRNA in contrast to RR-MS patients that had a reduced FOXP3 expression. These data are the first to demonstrate differences in function and FOXP3 expression of CD4(+)CD25(+) T cells from patients with RR- and SP-MS.

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