Analysis of FOXP3+ regulatory T cell subpopulations in peripheral blood and tissue of patients with systemic lupus erythematosus.

Regulatory T cells (Tregs) are critical mediators of immune tolerance, yet their involvement in the autoimmune disease systemic lupus erythematosus (SLE) is incompletely understood. We analyzed CD4+ T cell subpopulations with Treg-related phenotypes and their association with disease activity in peripheral blood (PB) and tissues of patients with SLE. In detail, we quantified subpopulations regarding CD25, FOXP3, CD62L, CCR6, CD27, CD45RA, and CD45RO expression in PB from 31 patients with SLE divided into two disease activity groups and 32 healthy controls using flow cytometry. CD4+ and FOXP3+ T cells in skin and kidney biopsies of patients with SLE were quantified by immunohistochemistry. CD4+CD25+/++FOXP3+ and CD4+CD25+CD45RA-/CD45RO+ T cell frequencies were significantly higher in PB from patients with active compared to inactive SLE. The fraction of CD4+CD25++FOXP3+ Tregs and CD4+CD25+CD45RA+/CD45RO- naïve Tregs was not significantly different between these groups. CD4+CD25++ Tregs from active SLE patients comprised significantly less CD27+ cells and more CCR6+ cells compared to patients with inactive SLE. The percentage of CD4+FOXP3+ T cells among inflammatory infiltrates in skin and kidney biopsies of SLE patients was not different from other inflammatory skin/kidney diseases. In conclusion, although CD4+FOXP3+ T cell frequencies in the inflamed tissues of SLE patients were comparable to other inflammatory diseases, distinct T cell subpopulations appeared misbalanced in PB of patients with active SLE. Here, cells phenotypically resembling activated T cells, but not Tregs, were increased compared to patients with inactive SLE. Within Tregs of patients with active SLE, markers related to Treg function and homing were altered.

CD8+ dendritic cell-mediated tolerance of autoreactive CD4+ T cells is deficient in NOD mice and can be corrected by blocking CD40L.

DCs are important mediators of peripheral tolerance for the prevention of autoimmunity. Chimeric αDEC-205 antibodies with attached antigens allow in vivo antigen-specific stimulation of T cells by CD8(+) DCs, resulting in tolerance in nonautoimmune mice. However, it is not clear whether DC-mediated tolerance induction occurs in the context of ongoing autoimmunity. We assessed the role of CD8(+) DCs in stimulation of autoreactive CD4(+) T cells in the NOD mouse model of type 1 diabetes. Targeting of antigen to CD8(+) DCs via αDEC-205 led to proliferation and expansion of ß-cell specific BDC2.5 T cells. These T cells also produced IL-2 and IFN-γ and did not up-regulate FoxP3, consistent with an activated rather than tolerant phenotype. Similarly, endogenous BDC peptide-reactive T cells, identified with I-A(g7) tetramers, did not become tolerant after antigen delivery via αDEC-205: no deletion or Treg induction was observed. We observed that CD8(+) DCs from NOD mice expressed higher surface levels of CD40 than CD8(+) DCs from C57BL/6 mice. Blockade of CD40-CD40L interactions reduced the number of BDC2.5 T cells remaining in mice, 10 days after antigen targeting to CD8 DCs, and blocked IFN-γ production by BDC2.5 T cells. These data indicate that the ability of autoreactive CD4(+) T cells to undergo tolerance mediated by CD8(+) DCs is defective in NOD mice and that blocking CD40-CD40L interactions can restore tolerance induction.

Interferon-α abrogates the suppressive effect of apoptotic cells on dendritic cells in an in vitro model of systemic lupus erythematosus pathogenesis.

OBJECTIVE: An increased incidence of apoptotic cells and an increased activation of dendritic cells (DC) may be involved in the pathogenesis of systemic lupus erythematosus (SLE). We investigated the characteristics of apoptotic neutrophils and monocyte-derived DC of patients with SLE, their interaction, and the influence of autoantibodies and inflammatory cytokines on this interaction. METHODS: Kinetics of neutrophil apoptosis and DC activation were studied by flow cytometry. To analyze the interaction of apoptotic cells with phagocytes, crossover coculture experiments were performed with DC from patients with SLE and apoptotic Jurkat T cells as well as with apoptotic neutrophils from patients with SLE and the monocytic cell line U937. SLE serum and cytokines were added to this coculture, and activation and suppression of DC were quantified by levels of inflammatory cytokine secretion. RESULTS: Apoptotic neutrophils and DC from patients with SLE showed no inherent defects compared to healthy controls, and the suppressive nature of their interaction was not affected. Autoantibodies as well as the inflammatory cytokines interleukin 17 (IL-17) and IL-1ß had no influence on the interaction in this setup. Interferon (IFN)-α, however, substantially reduced the suppressive effect of apoptotic cells on DC. CONCLUSION: The data suggest that aberrant immune reactivity in SLE is not generally due to an intrinsic defect in apoptotic cells, their processing, or their interaction with DC, but likely arises from the milieu in which this interaction takes place. Our study highlights the importance of IFN-α during early stages of SLE and its potential as a therapeutic target.