Abnormalities of B cell subsets in patients with systemic lupus erythematosus

Proteins derived from neutrophil extracellular traps may serve as self-antigens and mediate organ damage in autoimmune diseases

Neutrophils are the most abundant leukocytes in circulation and represent one of the first lines of defense against invading pathogens. Neutrophils possess a vast arsenal of antimicrobial proteins, which can be released from the cell by a death program termed NETosis. Neutrophil extracellular traps (NETs) are web-like structures consisting of decondensed chromatin decorated with granular and cytosolic proteins. Both exuberant NETosis and impaired clearance of NETs have been implicated in the organ damage of autoimmune diseases, such as systemic lupus erythematosus (SLE), small vessel vasculitis (SVV), and psoriasis. NETs may also represent an important source of modified autoantigens in SLE and SVV. Here, we review the autoimmune diseases linked to NETosis, with a focus on how modified proteins externalized on NETs may trigger loss of immune tolerance and promote organ damage.

Restoration of regulatory and effector T cell balance and B cell homeostasis in systemic lupus erythematosus patients through vitamin D supplementation

Introduction

Systemic lupus erythematosus (SLE) is a T and B cell-dependent autoimmune disease characterized by the appearance of autoantibodies, a global regulatory T cells (Tregs) depletion and an increase in Th17 cells. Recent studies have shown the multifaceted immunomodulatory effects of vitamin D, notably the expansion of Tregs and the decrease of Th1 and Th17 cells. A significant correlation between higher disease activity and lower serum 25-hydroxyvitamin D levels [25(OH)D] was also shown.

Methods

In this prospective study, we evaluated the safety and the immunological effects of vitamin D supplementation (100 000 IU of cholecalciferol per week for 4 weeks, followed by 100 000 IU of cholecalciferol per month for 6 months.) in 20 SLE patients with hypovitaminosis D.

Results

Serum 25(OH)D levels dramatically increased under vitamin D supplementation from 18.7±6.7 at day 0 to 51.4±14.1 (p<0.001) at 2 months and 41.5±10.1 ng/mL (p<0.001) at 6 months. Vitamin D was well tolerated and induced a preferential increase of naïve CD4⁺ T cells, an increase of regulatory T cells and a decrease of effector Th1 and Th17 cells. Vitamin D also induced a decrease of memory B cells and anti-DNA antibodies. No modification of the prednisone dosage or initiation of new immunosuppressant agents was needed in all patients. We did not observe SLE flare during the 6 months follow-up period.

Conclusions

This preliminary study suggests the beneficial role of vitamin D in SLE patients and needs to be confirmed in randomized controlled trials.

Interleukin 21 correlates with T cell and B cell subset alterations in systemic lupus erythematosus

OBJECTIVE

Systemic lupus erythematosus (SLE) is an autoimmune disease characterized by alterations of the B cell subset, global regulatory T cell (Treg) depletion, and an increase in Th17 cells. Interleukin 21 (IL-21) plays a critical role in T cell and B cell homeostasis. Our objective was to determine the implication of IL-21 and IL-21-producing CD4+ T cells in the pathogenesis of SLE.

METHODS

Twenty-five patients with SLE and 25 healthy donor controls were included. Analysis of CD4+ T cells producing IL-21, Th1, Th2, Th17, Treg, follicular helper T (TFH) cells, and B cells was performed in peripheral blood, and levels of cytokines were measured in culture supernatants.

RESULTS

Circulating CD4+ T cells producing IL-21 were markedly expanded in patients with SLE compared to controls and were correlated with increased Th17, decreased Treg, and increased memory B cells. CD4+ T cells producing IL-21 were composed of CXCR5+ and CXCR5-CD4+ T cell subsets. Both IL-21-producing CXCR5+CD4+ T cells and CXCR5-CD4+ T cells were increased in patients with SLE, the CXCR5-CD4+ subset correlating with Th17 cells and Treg, while the CXCR5+CD4+ subset was correlated with alterations of the B cell subset. The CXCR5+CD4+ subset comprised mainly circulating Bcl6+CXCR5+CD4+ TFH cells that were markedly expanded in patients with SLE and were correlated with increased circulating Bcl6+CXCR5+ germinal center B cells.

CONCLUSION

These findings suggest that IL-21, produced by distinct cellular CD4+ T cells, correlates with alterations of T cell and B cell subsets in SLE, and that targeting IL-21 could provide beneficial effects on both T cell and B cell alterations.

B-cell numbers and phenotype at clinical relapse following rituximab therapy differ in SLE patients according to anti-dsDNA antibody levels

Objectives. To correlate the kinetics of B-cell repopulation with relapse after B-cell depletion therapy in SLE patients and address whether variation in relapse rate, B-cell numbers and phenotype are related to anti-dsDNA antibody levels.

Methods. Sixty-one patients with refractory SLE were treated with a standard rituximab regimen. Clinical and serological measures of disease activity and B-cell numbers were assessed. B-cell phenotype was examined in a subgroup of patients by flow cytometry.

Results. Disease relapse was substantially delayed beyond B-cell repopulation, and early relapse was associated with a faster rate of repopulation. At relapse, B-cell numbers were significantly lower than at baseline in patients with high anti-dsDNA antibody levels (>100 IU/ml) but not in patients with low anti-dsDNA antibody levels. Of the patients with high anti-dsDNA antibodies at baseline, levels fell significantly only in those patients who remained in remission after repopulation. Relapse with high anti-dsDNA antibody levels was associated with an increased percentage of IgD⁻CD27^hi plasmablasts, whereas relapse with low anti-dsDNA antibody levels was accompanied by an increased percentage of IgD⁻CD27⁻ B cells.

Conclusion. Anti-dsDNA antibody levels distinguished two patient groups, which differ in their B-cell number and phenotype at relapse following rituximab, and suggest that different B-cell pathologies exist in SLE. The data imply that B-cell numbers should be kept very low for a sustained period in patients with high dsDNA binding, therefore justifying a more aggressive regimen.

Altered B cell homeostasis is associated with type I diabetes and carriers of the PTPN22 allelic variant

The PTPN22 genetic variant 1858T, encoding Lyp620W, is associated with multiple autoimmune disorders for which the production of autoantibodies is a common feature, suggesting a loss of B cell tolerance. Lyp620W results in blunted BCR signaling in memory B cells. Because BCR signal strength is tightly coupled to central and peripheral tolerance, we examined whether Lyp620W impacts peripheral B cell homeostasis in healthy individuals heterozygous for the PTPN221858T variant. We found that these subjects display alterations in the composition of the B cell pool that include specific expansion of the transitional and anergic IgD(+)IgM(-)CD27(-) B cell subsets. The PTPN22 1858T variant was further associated with significantly diminished BCR signaling and a resistance to apoptosis in both transitional and naive B cells. Strikingly, parallel changes in both BCR signaling and composition of B cell compartment were observed in type 1 diabetic subjects, irrespective of PTPN22 genotype, revealing a novel immune phenotype and likely shared mechanisms leading to a loss of B cell tolerance. Our combined findings suggest that Lyp620W-mediated effects, due in part to the altered BCR signaling threshold, contribute to breakdown of peripheral tolerance and the entry of autoreactive B cells into the naive B cell compartment.

Neutrophils in the pathogenesis and manifestations of SLE

Systemic lupus erythematosus (SLE) is an autoimmune disease of unclear etiology that affects mostly women of childbearing age. Profound abnormalities in both innate and adaptive immunity triggered by genetic and environmental factors are well documented to play an important part in the pathogenesis of SLE. Nonetheless, the role of neutrophils--the most abundant immune cell type--in the pathology of this disease has been unclear. Over the past decade, compelling evidence has emerged that implicates neutrophils in the initiation and perpetuation of SLE and also in the resultant organ damage frequently observed in patients with this disease. SLE-derived low-density granulocytes (LDGs) induce vascular damage and synthesize increased amounts of type I interferons and, as such, could play a prominent part in the pathogenesis of SLE. Furthermore, increased cell death and enhanced extracellular trap formation observed in SLE-derived neutrophils might have key roles in the induction of autoimmunity and the development of organ damage in patients with SLE. Together, these events could have significant deleterious effects and promote aberrant immune responses in this disease. This Review highlights the role of neutrophils in the pathogenesis of SLE, with a particular focus on the putative deleterious effects of LDGs and neutrophil extracellular trap formation.

An update on belimumab for the treatment of lupus

B-lymphocyte stimulator (BLyS), a homeostatic factor for B-cell differentiation and survival, has a major role in B-cell expansion and autoreactivity that characterize systemic lupus erythematosus (SLE). Belimumab, a BLyS-specific inhibitor, has shown promising evidence of efficacy in several preclinical and clinical studies in SLE. Two recent large randomized controlled trials yielded a significant positive effect of the drug compared to placebo in patients with active disease. In this review, we discuss basic aspects of B-cell and BLyS biology in SLE and summarize the evidence supporting a role of belimumab in SLE, from animal studies to phase III clinical trials.