Altered Expression of Fc and Complement Receptors on B Cells in Systemic Lupus Erythematosus

Aberrant expression of inhibitory receptors on B cells in patients with Graves' disease

The pathophysiological mechanism underlying Graves' disease (GD) remains incompletely understood. Inhibitory receptors on B cells are critical for humoral immunity, which plays a key role in GD pathogenesis. This study aimed to investigate B cell subsets distribution and inhibitory receptor expression on these subsets in GD patients. Peripheral blood was drawn from 41 healthy controls and 46 GD patients (21 patients with moderate GD, 25 patients with severe GD). B cell subset distribution and CD22, CD32b and CD72 expression on B cells were analyzed by flow cytometry. Serum cytokines were examined by enzyme-linked immunosorbent assay (ELISA). Compared with healthy controls, the naïve B cell percentage was increased, while the preswitched memory and conventional memory B cell percentages were decreased. The inhibitory receptors expression, especially CD32b, on B cell subsets was significantly decreased in patients with GD. In addition, the inhibitory receptors expression on B cell subsets from severe GD patients exhibited a decreasing trend compared with those from moderate GD patients. These results suggest that abnormal B cell subset distribution occurs in GD. Impaired inhibitory receptors, in particular CD32b, play a crucial role in GD pathogenesis and might be a therapeutic target to rebuild self-immune tolerance in GD.

Osteonecrosis in systemic lupus erythematosus: Systematic insight from the epidemiology, pathogenesis, diagnosis and management

Osteonecrosis (ON) is one of the serious and well recognized complicationscausing severe pain and disability in patients with systemic lupus erythematosus (SLE), and its manifestation and pathogenesis are only partially understood. This review provide an update of the recent progress in etiology, pathogenesis, diagnosis, and treatment of systemic lupus erythematosus related osteonecrosis (SLE-ON). Despite the concomitant use of corticosteroids, alcohol and obesity, the dysregulated immune micro-environment and the complex pathogenesis of SLE synergistically play important roles in the development of ON. Osteonecrosis of femoral head (ONFH) is the most often involved joint in SLE. The current classification and staging system of ONFH is based on imaging techniques, particularly relating to MRI and CT, for the identification and quantification of necrotic lesions. For SLE-ONFH patients, both SLE specific clinical symptoms and ONFH imaging findings should be comprehensively evaluated. Even though advances concerning bone grafting and arthroplasty procedures have resulted in improved clinical outcomes, early pharmacological treatment at the pre-collapse stage may prevent joint collapse and reduce the joint arthroplasty rate, and this needs to be accounted. Although some progress has been made, considerably more research is needed before we fully understand SLE-ONFH. Future treatments of SLE-ONFH may involve genetic or cell-based therapies that target potential biomarkers, and this will lead to effective measures for saving thefunction of hip joint and preventing osteonecrosis.

Lupus-like Disease in FcγRIIB-/- Mice Induces Osteopenia

Osteoporotic fracture is a major cause of morbidity in patients with systemic lupus erythematosus (SLE). Mice lacking Fc gamma receptor IIb (FcγRIIB) spontaneously develop lupus-like disease or SLE at 6-month-old. The aim of this study was to investigate whether FcγRIIB deletion induces osteopenia. μCT analysis indicated that deleting FcγRIIB did not affect cancellous bone microarchitecture in 3-month-old mice in which SLE had not yet developed. However, 6- and 10-month-old FcγRIIB^−/− males that developed an SLE-like phenotype were osteopenic and FcγRIIB deletion resulted in decreased cancellous bone volume. Histomorphometry confirmed a significant decrease in cancellous bone volume in 6- and 10-month-old FcγRIIB^−/− males. The osteoclast number was increased without any change in osteoblast number. In vitro assays indicated that deleting FcγRIIB increased osteoclast differentiation while alkaline phosphatase activity and mineralization were unaltered. These changes were associated with increases in steady-state mRNA levels for the osteoclast marker genes Trap and Ctsk. Moreover, FcγRIIB^−/− mice had higher level of serum TNFα, a proinflammatory cytokine. A soluble TNFα receptor, etanercept, prevented cancellous bone loss in FcγRIIB^−/− mice. Our results indicate that FcγRIIB indirectly regulates cancellous bone homeostasis following SLE development. FcγRIIB deletion induces inflammatory bone loss due to increased TNFα-mediated bone resorption without any change in bone formation in mice with SLE-like syndrome.

Differential immunoglobulin and complement levels in leprosy prior to development of reversal reaction and erythema nodosum leprosum

Background

Leprosy is a treatable infectious disease caused by Mycobacterium leprae. However, there is additional morbidity from leprosy-associated pathologic immune reactions, reversal reaction (RR) and erythema nodosum leprosum (ENL), which occur in 1 in 3 people with leprosy, even with effective treatment of M. leprae. There is currently no predictive marker in use to indicate which people with leprosy will develop these debilitating immune reactions. Our peripheral blood mononuclear cell (PBMC) transcriptome analysis revealed that activation of the classical complement pathway is common to both RR and ENL. Additionally, differential expression of immunoglobulin receptors and B cell receptors during RR and ENL support a role for the antibody-mediated immune response during both RR and ENL. In this study, we investigated B-cell immunophenotypes, total and M. leprae-specific antibodies, and complement levels in leprosy patients with and without RR or ENL. The objective was to determine the role of these immune mediators in pathogenesis and assess their potential as biomarkers of risk for immune reactions in people with leprosy.

Methodology/findings

We followed newly diagnosed leprosy cases (n = 96) for two years for development of RR or ENL. They were compared with active RR (n = 35), active ENL (n = 29), and healthy household contacts (n = 14). People with leprosy who subsequently developed ENL had increased IgM, IgG1, and C3d-associated immune complexes with decreased complement 4 (C4) at leprosy diagnosis. People who developed RR also had decreased C4 at leprosy diagnosis. Additionally, elevated anti-M. leprae antibody levels were associated with subsequent RR or ENL.

Conclusions

Differential co-receptor expression and immunoglobulin levels before and during immune reactions intimate a central role for humoral immunity in RR and ENL. Decreased C4 and elevated anti-M. leprae antibodies in people with new diagnosis of leprosy may be risk factors for subsequent development of leprosy immune reactions.

One in three people with leprosy develop an immune reaction, which worsen quality of life. Reactions occur despite effective treatment of the causative bacteria of leprosy, Mycobacterium leprae, with antibiotics. These reactions cause worsening skin lesions and additional nerve damage. Reactions can be chronic and recurrent, and may necessitate years of treatment with high dose corticosteroids. Our research focuses on why certain people develop these reactions while others do not. We found that people who have higher antibodies to M. leprae when they are diagnosed with leprosy are more likely to develop immune reactions in the two years after diagnosis. Also, we identify that C4 levels in the blood may be useful for monitoring the development and progression of leprosy reactions. These may be ways to identify who is at highest risk for leprosy immune reactions before they occur.

Mechanisms of tissue injury in lupus nephritis

Systemic lupus erythematosus is a prototypic autoimmune disease characterized by autoantibody production and immune complex formation/deposition in target organs such as the kidney. Resultant local inflammation then leads to organ damage. Nephritis, a major cause of morbidity and mortality in patients with lupus, occurs in approximately 50% of lupus patients. In the present review, we provide an overview of the current research and knowledge concerning mechanisms of renal injury in both lupus-prone mouse models and human lupus patients.

Pathophysiology and clinical spectrum of infections in systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is an inflammatory and multisystemic autoimmune disorder characterized by an uncontrolled autoreactivity of B and T lymphocytes leading to the production of autoantibodies against self-directed antigens and tissue destruction. Environmental factors, such as infections, which are an important cause of morbidity and mortality, are potential triggers of the disease. This article discusses bacterial, viral, and opportunistic microorganism infections in SLE, and the role of immunosuppressive therapy and immunodeficiencies in the disease.

Altered B cell receptor signaling in human systemic lupus erythematosus

Regulation of B cell receptor signaling is essential for the development of specific immunity while retaining tolerance to self. Systemic lupus erythematosus (SLE) is characterized by a loss of B cell tolerance and the production of anti-self antibodies. Accompanying this break down in tolerance are alterations in B cell receptor signal transduction including elevated induced calcium responses and increased protein phosphorylation. Specific pathways that negatively regulate B cell signaling have been shown to be impaired in some SLE patients. These patients have reduced levels of the kinase Lyn in lipid raft microdomains and this reduction is inversely correlated with increased CD45 in lipid rafts. Function and expression of the inhibitory immunoglobulin receptor FcgammaRIIB is also reduced in Lupus IgM- CD27+ memory cells. Because the relative contribution of different memory and transitional B cell subsets can be abnormal in SLE patients, we believe studies targeted to well defined B cell subsets will be necessary to further our understanding of signaling abnormalities in SLE. Intracellular flow cytometric analysis of signaling is a useful approach to accomplish this goal.

Physiological up-regulation of inhibitory receptors Fc gamma RII and CR1 on memory B cells is lacking in SLE patients

Under physiological conditions immune complexes (IC) are efficiently cleared from the circulation and meanwhile provide important feedback signals for the immune system via Fc gamma Rs and complement receptors. Dysregulation of these mechanisms have been implicated in conditions where IC concentrations reach pathological levels and inflict diseases, like systemic lupus erythematosus (SLE). Our aim was to compare distinct sub-populations of CD19(+) B cells of healthy individuals and SLE patients with regard to their expression of Fc gamma R type II (Fc gamma RII, CD32), complement receptor type 1 (CR1, CD35) and complement receptor type 2 (CR2, CD21) and sIgG/IgM. The following four groups of peripheral CD19(+) B cells were investigated: IgM(+)/CD27(-) naive, IgM(+)/CD27(+) and IgM(-)/CD27(+) memory cells and CD27(high) plasmablasts. We demonstrate that the expression of the inhibitory receptors Fc gamma RII and CR1 is up-regulated on peripheral memory B cells of healthy controls, whereas this up-regulation is considerably impaired on the memory B cells of SLE patients. This reduction affects both the IgM(+) and switched memory B cells. We found a striking difference between the expression of complement receptors CD21 and CD35; namely, no up-regulation of CD21 occurred on the memory B cells of healthy donors, and its decreased expression in SLE patients was characteristic for both the CD27(-) naive and the CD27(+) memory B-cell populations. Our results clearly demonstrate that the previously reported reduced expression of IC-binding receptors is mainly due to the disturbed memory compartment; however, the higher frequency of CD19(+)/CD27(high)/sIg(low) plasmablasts expressing minimal levels of these receptors also contributes to this diminution.