Establishment of a transgenic mouse model with liver-specific expression of secretory immunoglobulin D

High serum immunoglobulin D levels in systemic lupus erythematosus: more to be found?

INTRODUCTION

Many studies have shown that serum immunoglobulin D (IgD) is usually increased in autoimmune diseases. The potential role of IgD in systemic lupus erythematosus (SLE) is still unclear. Our study aimed to compare the serum IgD levels of SLE with different population and to evaluate the relationship between serum IgD and SLE.

METHODS

Fifty SLE patients, 40 non-SLE chronic kidney disease (CKD) patients, and 50 healthy volunteers were enrolled in this study. Serum IgD levels were analyzed by ELISA assay and compared between groups. The correlation of serum IgD and SLE disease were evaluated. The ability of serum IgD to predict SLE was analyzed by graphing receiver operating characteristic curves.

RESULTS

Serum IgD levels were significantly higher in SLE patients compared to non-SLE CKD and healthy controls (7436.1 ± 5862.1 vs. 4517.8 ± 5255.2 vs. 4180.4 ± 4881 ng/mL, p = 0.01, p = 0.002, respectively), and in patients with high SLE Disease Activity Index (SLEDAI) scores compared with those with low scores (8572.9 ± 5968.7 vs. 5020.4 ± 4972.5 ng/mL, p = 0.044). High level of inflammatory cytokines and decreased circulating basophil counts were found in SLE patients (p < 0.05). No correlations was identified between serum IgD levels and SLEDAI scores (p > 0.05). Serum IgD was noninferior to IgG or IgE in discriminating SLE with an area under the curve of 0.672 (95% CI, 0.59-0.75).

CONCLUSIONS

Serum IgD levels are significantly elevated in SLE patients with high SLEDAI scores. Simultaneous occurrence of increased inflammatory cytokines and decreased basophil counts highlights the potential role of IgD-targets interaction in SLE pathogenesis. Key points • Total serum IgD levels were elevated in SLE patients. • High IgD levels were significantly higher in SLE patients with high SLEDAI scores. • The ability of serum IgD was equivalent to IgG or IgE in discriminating SLE from CKD and healthy adult.

IgD promotes pannus formation by activating Wnt5A-Fzd5-CTHRC1-NF-κB signaling pathway in FLS of CIA rats and the regulation of IgD-Fc-Ig fusion protein

Rheumatoid arthritis (RA) is a systemic autoimmune disease characterized by joint inflammation, synovial hyperplasia, cartilage degeneration, bone erosion, and pannus. Immunoglobulin D (IgD) plays an important role in autoimmune diseases although the content of it in vivo is low. Increased concentrations of anti-IgD autoantibodies have been detected in many RA patients. IgD-Fc-Ig fusion protein is constructed by connecting human IgD Fc domain and IgG1 Fc domain, which specifically block the IgD/ IgDR pathway and regulate the function of cells expressing IgDR to treat RA. The expression levels of Wnt5A and Frizzled 5 are higher in RA synovial tissue specimens. The complex of Wnt5A-Fzd5-LRP5/6-CTHRC1 promotes the expression of hypoxia inducible factor-1α by activating nuclear factor kappa-B (NF-κB), leading to high expression of VEGF and participating in angiogenesis. VEGF is the strongest angiogenic factor found so far. Here, we aimed to explore whether IgD participates in synovitis by binding to IgDR and regulating the activation of Wnt5A-Fzd5-CTHRC1-NF-κB signaling pathway in fibroblast synovial cells (FLSs), whether IgD-Fc-Ig fusion protein inhibits VEGF production in FLS of CIA and explore mechanism. We found that IgDR is expressed on MH7A and FLS. IgD promotes VEGF expression by activating Wnt5A-Fzd5-CTHRC1-NF-κB signaling pathway in MH7A and FLS. After activation of Fzd5 with Wnt5A, IgD-Fc-Ig reduced VEGF-A level in the culture supernatant of MH7A stimulation by IgD. The expressions of CTHRC1, Fzd5, p-P65 and VEGF in MH7A and FLSs were down-regulated after IgD-Fc-Ig treatment. IgD-Fc-Ig suppressed the combination of CTHRC1 and Fzd5 as well. By using the animal model, we demonstrated that IgD-Fc-Ig suppress ankle CTHRC1 and Fzd5 production resulted in inhibition of index of joint inflammation of CIA rats, which were consistent with vitro results. Conclusively, IgD-Fc-Ig inhibits IgD and Wnt5A-induced angiogenesis and joint inflammation by suppressing the combination of CTHRC1 and Fzd5. Our results show that IgD-Fc-Ig exerts its suppressive effect on IgD and Wnt5A by Wnt5A-Fzd5-CTHRC1-NF-κB signaling pathway.

The prospects for targeting FcR as a novel therapeutic strategy in rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic systemic autoimmune disease characterized by synovial membrane hyperplasia, infiltration of inflammatory cells and bone tissue destruction. Although there have been many measures taken for RA therapy in recent years, they are not sufficiently safe or effective. Thus, it is very important to develop new drugs and slow down damage to other healthy organs in the case of RA. Lately, immunoglobulin Fc receptors (FcRs), such as the IgG Fc receptor (FcγR), IgA Fc receptor (FcαR), and IgD Fc receptor (FcδR), have been found to be involved in inducing or suppressing arthritis. FcRs interacting with immune complexes (ICs) are a key factor in the etiopathogenesis of RA. Therefore, an increasing number of methodsfor the targeted treatment of RA with FcRs are emerging, such as recombinant soluble FcγRs, recombinant multimeric Fc fragments and monoclonal antibodies, and have been demonstrated to significantly improve RA symptoms. Simultaneously, certain kinases involved in the downstream signaling of FcRs can also be a target for the treatment of RA, such as Syk and Btk inhibitors. An overview of these FcRs is provided in this review, including a description of FcR-related functions, signaling pathways, and potential FcR-targeting molecules for RA therapy. To date, the initial results of those developed FcR-targeting molecules have been promising. With this, FcRs might offer a better alternative to RA medication. Additionally, further pharmacological characterization and a better understanding of the unique mechanisms of FcR-targeting molecules are necessary.

IgD-Fc-Ig fusion protein, a new biological agent, inhibits T cell function in CIA rats by inhibiting IgD-IgDR-Lck-NF-κB signaling pathways

IgD-Fc-Ig fusion protein, a new biological agent, is constructed by linking a segment of human IgD-Fc with a segment of human IgG1-Fc, which specifically blocks the IgD-IgDR pathway and selectively inhibits the abnormal proliferation, activation, and differentiation of T cells. In this study we investigated whether IgD-Fc-Ig exerted therapeutic effects in collagen-induced arthritis (CIA) rats. CIA rats were treated with IgD-Fc-Ig (1, 3, and 9 mg/kg) or injected with biological agents etanercept (3 mg/kg) once every 3 days for 40 days. In the PBMCs and spleen lymphocytes of CIA rats, both T and B cells exhibited abnormal proliferation; the percentages of CD3⁺ total T cells, CD3⁺CD4⁺ Th cells, CD3⁺CD4⁺CD25⁺-activated Th cells, Th1(CD4⁺IFN-γ⁺), and Th17(CD4⁺IL-17⁺) were significantly increased, whereas the Treg (CD4⁺CD25⁺Foxp3⁺) cell percentage was decreased. IgD-Fc-Ig administration dose-dependently decreased the indicators of arthritis; alleviated the histopathology of spleen and joint; reduced serum inflammatory cytokines levels; decreased the percentages of CD3⁺ total T cells, CD3⁺CD4⁺ Th cells, CD3⁺CD4⁺CD25⁺-activated Th cells, Th1 (CD4⁺IFN-γ⁺), and Th17(CD4⁺IL-17⁺); increased Treg (CD4⁺CD25⁺Foxp3⁺) cell percentage; and down-regulated the expression of key molecules in IgD-IgDR-Lck-NF-κB signaling (p-Lck, p-ZAP70, p-P38, p-NF-κB65). Treatment of normal T cells with IgD (9 μg/mL) in vitro promoted their proliferation. Co-treatment with IgD-Fc-Ig (0.1–10 μg/mL) dose-dependently decreased IgD-stimulated T cell subsets percentages and down-regulated the IgD-IgDR-Lck-NF-κB signaling. In summary, this study demonstrates that IgD-Fc-Ig alleviates CIA and regulates the functions of T cells through inhibiting IgD-IgDR-Lck-NF-κB signaling.

CP-25 Attenuates the Activation of CD4+ T Cells Stimulated with Immunoglobulin D in Human

Researchers have shown that the level of immunoglobulin D (IgD) is often elevated in patients with autoimmune diseases. The possible roles of IgD on the function of human T cell activation are still unclear. Paeoniflorin-6′-O-benzene sulfonate (code: CP-25), the chemistry structural modifications of paeoniflorin, was a novel drug of anti-inflammation and immunomodulation. The aims of this study were to determine if human CD4⁺ T cells could be activated by IgD via the IgD receptor (IgDR)-Lck pathway and whether the novel compound CP-25 could affect the activation of T cells by regulating Lck. Human CD4⁺ T cells were purified from peripheral blood mononuclear cells using microbeads. T cell viability and proliferation were detected by Cell Counting Kit-8 and CFSE Cell Proliferation Kit. Cytokines secreted by T cells were assessed with the Quantibody Human Inflammation Array. The binding affinity and expression of IgDR on T cells were detected by flow cytometry, and protein expression of IgDR, Lck, and P-Lck were analyzed by western blot. IgD was shown to bind to IgDR on CD4⁺ T cells in a concentration-dependent manner and stimulate the activation and proliferation of these cells by enhancing phosphorylation of the activating tyrosine residue of Lck (Tyr³⁹⁴). CP-25 inhibited the IgD-stimulated activation and proliferation of CD4⁺ T cells, as well as the production of inflammatory cytokines; it was thus suggested that this process might be related to the downregulation of Lck (Tyr³⁹⁴) phosphorylation. These results demonstrate that IgD amplifies the activation of CD4⁺ T cells, which could be mediated by Lck phosphorylation. Further, CP-25, via its ability to modulate Lck, is a novel potential therapeutic agent for the treatment of human autoimmune diseases.

The immunoglobulin D Fc receptor expressed on fibroblast-like synoviocytes from patients with rheumatoid arthritis contributes to the cell activation

Immunoglobulin IgD might play an important role in autoimmune diseases, but the function of IgD has remained elusive, despite multiple attempts to define its biological function. Fibroblast-like synoviocytes (FLSs) are specialized cells of the synovium that play a key role in the pathogenesis of rheumatoid arthritis (RA). In this study we explored the possible roles of excessive IgD expression on the function of FLSs from RA patients (RA-FLSs). We showed that IgD Fc receptor (IgDR) was constitutively expressed on FLSs, and was significantly elevated in RA-FLSs compared with FLSs prepared from synovial tissues of healthy controls (HC-FLSs). Furthermore, IgDR was mainly detected on the cell surface and in the cytoplasm. We further detected the intrinsic binding affinity of IgD to IgDR on HC-FLSs with an equilibrium dissociation constant (K_D) of 0.067 nmol/L. Incubation of RA-FLSs with IgD (1-10 μg/mL) for 48 h dose-dependently promoted the expression of IgDR, and stimulated the production of inflammatory cytokines and chemokines, such as IL-1β, IL-6, monocyte chemotactic protein (MCP)-1, TNF-α and receptor activator of nuclear factor-κB ligand (RANKL), thus potentially contributing to IgD-IgDR crosslinking. Moreover, incubation with IgD (0.1-10 μg/mL) for 48 h dose-dependently enhanced viability for both HC-FLSs and RA-FLSs. Our results demonstrate that IgDR is expressed on RA-FLSs and contributes to the activation of FLSs, and suggest that IgD-IgDR is a potential novel immunotherapeutic target for the management of RA.

The Elevated Secreted Immunoglobulin D Enhanced the Activation of Peripheral Blood Mononuclear Cells in Rheumatoid Arthritis

Immunoglobulin D (IgD) is a surface immunoglobulin that is expressed as either membrane IgD (mIgD) or secreted IgD (sIgD). Researchers have shown that sIgD is often elevated in patients with autoimmune diseases. The possible roles of sIgD on the function of peripheral blood mononuclear cells (PBMCs) in rheumatoid arthritis (RA) are still unclear. In this study, we compared the expression of sIgD, mIgD and IgD receptor (IgDR) in RA patients and healthy controls, and investigated the effect of sIgD on the function of PBMCs. We found that the levels of sIgD, mIgD and IgDR were significantly higher in RA patients compared with healthy controls. The concentrations of sIgD were positively correlated with soluble receptor activator of nuclear factor-κB ligand (sRANKL), rheumatoid factor (RF) and C-reactive protein (CRP) in RA patients. Strikingly, IgD could enhance the proliferation of PBMCs and induce IL-1α, IL-1β, TNF-α, IL-6 and IL-10 production from PBMCs. Moreover, the percentage of activated T cell subsets (CD4⁺CD69⁺, CD4⁺CD154⁺) and activated B cell subsets (CD19⁺CD23⁺, CD19⁺CD21⁺, CD19⁺IgD⁺ and CD19^-CD138⁺) were increased by IgD. The percentage of unactivated T cell subset (CD4⁺CD62L⁺) and immature B cell subset (CD19⁺IgM⁺IgD^-) were decreased by IgD in PBMCs. Furthermore, the expressions of IgDR on T and B cells were significantly increased by treatment with IgD. Our results demonstrate that IgD enhanced the activation of PBMCs, which may contribute to RA pathogenesis. Therefore, IgD could be a potential novel immunotherapeutic target for the management of RA.

Splicing mutation in MVK is a cause of porokeratosis of Mibelli

Porokeratosis is a chronic skin disorder characterized by the presence of patches with elevated, thick, keratotic borders, with histological cornoid lamella. Classic porokeratosis of Mibelli (PM) frequently appears in childhood with a risk of malignant transformation. Disseminated superficial actinic porokeratosis (DSAP) is the most common subtype of porokeratosis with genetic heterogeneities, and mevalonate kinase gene (MVK) mutations have been identified in minor portion of DSAP families of Chinese origin. To confirm the previous findings about MVK mutations in DSAP patients and test MVK's role(s) in PM development, we performed genomic sequence analysis for 3 DSAP families and 1 PM family of Chinese origin. We identified a splicing mutation of MVK gene, designated as c.1039+1G>A, in the PM family. No MVK mutations were found in three DSAP families. Sequence analysis for complementary DNA templates from PM lesions of all patients revealed a mutation at splice donor site of intron 10, designated as c.1039+1G>A, leading to the splicing defect and termination codon 52 amino acids after exon 10. Although no MVK mutations in DSAP patients were found as reported previously, we identified MVK simultaneously responsible for PM development.