The objective of the study was that the regulatory T cells (Treg) that specialize in the suppression of immune responses might be critically involved in the pathogenesis of autoimmune disease. As for systemic lupus erythematosus (SLE), however, published data concerning Treg phenotype and function are partly conflicting. We therefore performed quantitative and qualitative analyses of naturally occurring CD4(+)CD25(+) Treg from SLE patients as compared with healthy controls (HC) in order to further elucidate the role of Treg in this systemic autoimmune disease. The phenotype of peripheral blood CD4(+)CD25(+) Treg was determined by flow cytometry (FACS) in SLE patients and HC. Treg were isolated from SLE patients and HC and their functional capacity was analyzed in suppression assays. Phenotypic and functional data were correlated with clinical data. Decreased proportions of CD4(+) Treg with high-level expression of CD25 (CD4(+)CD25(hi)) were observed in active and inactive SLE patients (0.96 +/- 0.08 and 1.17 +/- 0.08%, respectively) as compared with HC (2 +/- 0.1%). In contrast to HC, Treg from SLE patients displayed an activated phenotype as determined by the expression of CD69, CD71 and HLA-DR. The suppressive capacity of isolated Treg from SLE patients, however, was significantly reduced as compared with HC. Proportions of CD4(+)CD25(hi) T cells and the suppressive capacity of Treg were inversely correlated with the clinical disease activity in SLE patients. Our data describe quantitative and qualitative defects of Treg in SLE patients. These deficiencies might contribute to the breakdown of self-tolerance and the development of the autoimmune response in SLE patients.

Conclusion. In addition to supporting the role of IFNs in SLE immunopathogenesis in general, the findings of the present study support a role of IFN␥ in this disease.Type I interferons (e.g., IFN␣) and type II IFN (IFN␥) have both been implicated in the immunopathogenesis of systemic lupus erythematosus (SLE). IFN␣ and IFN␥ serum levels are increased (1-5), and IFN messenger RNA (mRNA) signatures are expressed in the peripheral blood cells of SLE patients (6-8). IFN␣ and IFN␥ are known to induce SLE flares and druginduced lupus (9-11). In murine models of the disease, both IFN␣ and IFN␥ may be pathogenetically important (12-15), and, especially, a deficiency in either IFN␥ or the IFN␥ receptor (IFN␥R) totally abates the disease process (16)(17)(18)(19).IFNs act on a variety of cells, including lymphocytes and monocytes (20,21). The biologic effects of IFN␣ and IFN␥ are mediated via the phosphorylation, and thus the activation, of members of the STAT family

Our data suggest that the expression of Foxp3 on CD4(+) T cells in patients with SLE, at least to some extent, reflects the activation of CD4(+) T cells due to underlying disease activity and does not necessarily indicate a functional regulatory T cell capacity.