The quantitative analysis of peripheral blood FOXP3-expressing T cells in systemic lupus erythematosus and rheumatoid arthritis patients

Background Expressed in naturally occurring CD4(+)CD25(+) regulatory T cells, FoxP3 plays an important role in maintaining immune tolerance. We therefore evaluated the possibility that the peripheral blood FOXP3(+) T-cell deficiency is associated with systemic lupus erythematosus (SLE) and rheumatoid arthritis (RA). Materials and methods The FOXP3 expression in peripheral blood T cells were evaluated and correlated to the CD4 and CD25 expression by flow cytometric analysis. Cell frequencies of FOXP3(+) T cells among CD4(+) T cells and absolute FOXP3(+) T cell counts in SLE and RA patients were determined for the statistical comparison with those in normal controls, and their correlation with disease activities in SLE patients was evaluated. The FOXP3 transcript levels in peripheral blood mononuclear cells (PBMCs) were also determined to correlate the FOXP3(+) T-cell quantity and to evaluate the possible dysregulation in the expression of two FOXP3 mRNA variants in patients. Results SLE patients had the higher FOXP3(+) T-cell frequency and absolute CD4(+)CD25(-)FOXP3(+) cell count than normal individuals, and the frequencies of CD4(+)CD25(+)FOXP3(+) and CD4(+)FOXP3(+) cells were positively correlated with the disease activities in SLE patients. In contrast, the differences in frequencies and absolute counts of FOXP3(+) T cells between normal controls and RA patients were found to be insignificant. Moreover, SLE and RA patients appear to express two FOXP3 transcript variants in peripheral blood mononuclear cells at the levels similar to normal individuals. Conclusions The peripheral blood FOXP3(+) T-cell frequency among CD4(+) T cells is altered in SLE patients with the active disease activity. Therefore, the analysis on peripheral blood FOXP3(+) T cells may be useful for the evaluation of lupus disease activity.