Abstract
Impaired suppressive capacity of CD4+CD25+FOXP3+ regulatory T cells (Treg) from peripheral blood of patients with multiple sclerosis (MS) has been reported by multiple laboratories. It is, however, currently unresolved whether Treg dysfunction in MS patients is limited to reduced control of peripheral T cell activation since most studies analyzed peripheral blood samples only. Here, we assessed early active MS lesions in brain biopsies obtained from 16 patients with MS by FOXP3 immunohistochemistry. In addition, we used six-color flow cytometry to determine numbers of Treg by analysis of FOXP3/CD127 expression in peripheral blood and cerebrospinal fluid (CSF) of 17 treatment-naïve MS patients as well as quantities of apoptosis sensitive CD45ROhiCD95hi cells in circulating and CSF Treg subsets. Absolute numbers of FOXP3+ and CD4+ cells were rather low in MS brain lesions and Treg were not detectable in 30% of MS biopsies despite the presence of CD4+ cell infiltrates. In contrast, Treg were detectable in all CSF samples and Treg with a CD45ROhiCD95hi phenotype previously shown to be highly apoptosis sensitive were found to be enriched in the CSF compared to peripheral blood of MS patients. We suggest a hypothetical model of intracerebral elimination of Treg by CD95L-mediated apoptosis within the MS lesion.
Highlights
Multiple Sclerosis (MS) is considered a prototype autoimmune disease
Whereas putative autoreactive T cells are thought to exhibit resistance towards apoptosis [10,11,12,13] Treg from MS patients are highly sensitive to induction of CD95L-mediated apoptotic cell death as we have shown previously [14,15]
When we analyzed the percentage of CD95hiCD45ROhi Treg in a cohort of 17 MS patients we found a significantly (p = 0.019) higher percentage of such apoptosis-prone Treg in cerebrospinal fluid (CSF) compared to peripheral blood (Fig. 2C)
Summary
Multiple Sclerosis (MS) is considered a prototype autoimmune disease. Analysis of the autoimmune response is predominantly studied in peripheral blood of MS patients or carried out in animal models which share some similarities with MS such as EAE. Whereas putative autoreactive T cells are thought to exhibit resistance towards apoptosis [10,11,12,13] Treg from MS patients are highly sensitive to induction of CD95L-mediated apoptotic cell death as we have shown previously [14,15]. This phenotype is not MS-specific since Treg from healthy donors exhibit similar apoptosis sensitivity and Treg turned out to be the most short-lived cells among T cells populations [15,16]. Our current knowledge on Treg in the human CNS is sparse and nearly no data is available on natural FOXP3+ Treg distribution in the MS lesion [19]
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