Systemic lupus erythematosus exhibits a dynamic and continuum spectrum of effector/regulatory T cells

Abstract

Objective: The identification of regulatory T cells (Treg cells) as CD4⁺CD25^high cells may be upset by the increased frequency of activated effector T cells (Teff cells) in inflammatory diseases such as systemic lupus erythematosus (SLE). This study aimed to evaluate the frequency of T-cell subsets according to the expression of CD25 and CD127 in active (A-SLE) and inactive SLE (I-SLE).

Methods: Peripheral blood mononuclear cells (PBMCs) from 26 A-SLE patients (SLE Disease Activity Index (SLEDAI) = 10.17 ± 3.7), 31 I-SLE patients (SLEDAI = 0), and 26 healthy controls (HC) were analysed by multicolour flow cytometry.

Results: CD25^high cell frequency was increased in A-SLE (5.2 ± 5.7%) compared to I-SLE (3.4 ± 3.4%) and HC (1.73 ± 0.8%) (p < 0.01). However, the percentage of FoxP3⁺ cells in the CD25^high subset was decreased in A-SLE (24.6 ± 16.4%) compared to I-SLE (33.7 ± 16) and HC (45 ± 25.1%) (p < 0.01). This was partly due to the increased frequency of Teff cells (CD25^highCD127⁺FoxP3^Ø) in A-SLE (10.7 ± 7.3%) compared to I-SLE (8.5 ± 6.5) and HC (6.1 ± 1.8%) (p = 0.02). Hence the frequency of Treg cells (CD25^+/highCD127^low/ØFoxP3⁺) was equivalent in A-SLE (1.4 ± 0.8%), I-SLE (1.37 ± 1.0%), and HC (1.13 ± 0.59%) (p = 0.42). A-SLE presented an increased frequency of CD25⁺CD127⁺FoxP3⁺ and CD25^ØFoxP3⁺CD127^low/Ø T cells, which may represent intermediate phenotypes between Treg and Teff cells.

Conclusions: The present study has provided data supporting normal Treg cell frequency in A-SLE and I-SLE as well as increased frequency of Teff cells in A-SLE. This scenario reflects a Treg/Teff ratio imbalance that may favour the inflammatory phenotype of the disease. In addition, the increased frequency of T cells with putative intermediate phenotypes may be compatible with a highly dynamic immune system in SLE.

Acknowledgements

This work was funded by grants from FAPESP (06/51934-0; 07/51349-2) and CNP-q (2008-476356/2008-3).