Regulatory T cells in SLE patients and their unasected relatives : phenotypic characterization and genetic effects

Abstract

Systemic Lupus Erytematosus (SLE) is an autoimmune disease characterized by the production of antibodies against self, indicating a loss of self recognition and consequently self tolerance. Deficient regulatory T cells (Tregs) have been implicated in this loss of self tolerance with several mechanisms that are thought to play a role in their impairment. The aim of this study was to characterize Treg phenotypes comparing results from unaffected first degree relatives and SLE patients. Therefore, cytometric analysis was performed in Tregs using peripheral blood from SLE patients and unaffected first degree relatives and also from healthy donors. In parallel SNPs in specific genes were typed, namely IL2RA, IL2RB, IL2, IL6, CTLA4, PTPN22 and PTTG1. The cytometric Treg phenotypes were analyzed and correlated with the genotypes. Furthermore, cell cultures were performed to induce Foxp3 expressing cells from naïve effector Th cells using anti- CD3 stimulation and TGF-β1. In agreement with other recent studies, surface CD25, recently proposed as a marker for activation in Tregs, was clearly reduced in relatives and patients. The cytometric results also revealed a higher frequency of Foxp3+ cells in patients due to an expansion of the Foxp3low population. In contrast, the frequency of Foxp3+ in relatives was lower due to a decrease of the Foxp3high population. This reduction of CD25+Foxp3high cells in relatives was interpreted as a relative exhaustion of these cells due to accelerated activation. Genetic effects in loci encoding IL-2, components of the IL2 receptor (IL2R) as well as in PTTG1 supported this interpretation. Particularly, IL2RA genetic variation that in controls was favoring an increase of CD25 was associated with a lower frequency of Foxp3high in relatives. In the patients, genetic effects of an IL6 SNP appeared to contribute to the inflammatory condition and possibly influenced the increased frequency of Foxp3low. Moreover, in the patients group there was an indication that naïve Th cells had less predisposition to become activated when compared to the relatives and control groups in vitro. In conclusion, this study allowed to characterize some phenotypes in the unaffected relatives, a poorly studied group. The IL2 receptor system seemed to be involved in a compensatory effect of Tregs in this group. Other genetic factors associated with risk for SLE seemed to have a negative effect. The relation of the defective in vitro T-cell activation in patients with Treg properties remains to be studied. However, other studies should be performed, especially with the relatives to understand the mechanisms that allow this group to remain unaffected.