Fc-specific reticulo-endothelial clearance in systemic lupus erythematosus and glomerulonephritis

The shared circulating diagnostic biomarkers and molecular mechanisms of systemic lupus erythematosus and inflammatory bowel disease

Background

Systemic lupus erythematosus (SLE) is a multi-organ chronic autoimmune disease. Inflammatory bowel disease (IBD) is a common chronic inflammatory disease of the gastrointestinal tract. Previous studies have shown that SLE and IBD share common pathogenic pathways and genetic susceptibility, but the specific pathogenic mechanisms remain unclear.

Methods

The datasets of SLE and IBD were downloaded from the Gene Expression Omnibus (GEO). Differentially expressed genes (DEGs) were identified using the Limma package. Weighted gene coexpression network analysis (WGCNA) was used to determine co-expression modules related to SLE and IBD. Pathway enrichment was performed using Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis for co-driver genes. Using the Least AbsoluteShrinkage and Selection Operator (Lasso) regressionand Support Vector Machine-Recursive Feature Elimination (SVM-RFE), common diagnostic markers for both diseases were further evaluated. Then, we utilizedthe CIBERSORT method to assess the abundance of immune cell infiltration. Finally,we used the single-cell analysis to obtain the location of common diagnostic markers.

Results

71 common driver genes were identified in the SLE and IBD cohorts based on the DEGs and module genes. KEGG and GO enrichment results showed that these genes were closely associated with positive regulation of programmed cell death and inflammatory responses. By using LASSO regression and SVM, five hub genes (KLRF1, GZMK, KLRB1, CD40LG, and IL-7R) were ultimately determined as common diagnostic markers for SLE and IBD. ROC curve analysis also showed good diagnostic performance. The outcomes of immune cell infiltration demonstrated that SLE and IBD shared almost identical immune infiltration patterns. Furthermore, the majority of the hub genes were commonly expressed in NK cells by single-cell analysis.

Conclusion

This study demonstrates that SLE and IBD share common diagnostic markers and pathogenic pathways. In addition, SLE and IBD show similar immune cellinfiltration microenvironments which provides newperspectives for future treatment.

Estrogen receptor alpha promotes lupus in (NZB×NZW)F1 mice in a B cell intrinsic manner

Lupus is a systemic autoimmune disease characterized by the production of autoreactive antibodies against nuclear antigens. Women are disproportionately affected by lupus, and this sex bias is thought to be due, in large part, to the ability of estrogens to promote lupus pathogenesis. Previously, we have shown that global deletion of estrogen receptor alpha (ERα) significantly attenuated loss of tolerance, immune cell activation, autoantibody production, and the development of lupus nephritis. Here we show that targeted deletion of ERα specifically in B cells retards production of pathogenic autoantibodies and the development of nephritis in lupus-prone (NZB×NZW)F1 mice. Furthermore, we observed that ERα deletion in B cells was associated with decreased B cell activation in young, pre-autoimmune (NZB×NZW)F1 females. Altogether, these data suggest that ERα acts in a B cell-intrinsic manner to control B cell activation, autoantibody production, and lupus nephritis.

The genetics of lupus: a functional perspective

Systemic lupus erythematosus (SLE) is an autoimmune disease with a strong genetic component and is characterized by chronic inflammation and the production of anti-nuclear auto-antibodies. In the era of genome-wide association studies (GWASs), elucidating the genetic factors present in SLE has been a very successful endeavor; 28 confirmed disease susceptibility loci have been mapped. In this review, we summarize the current understanding of the genetics of lupus and focus on the strongest associated risk loci found to date (P <1.0 × 10−8). Although these loci account for less than 10% of the genetic heritability and therefore do not account for the bulk of the disease heritability, they do implicate important pathways, which contribute to SLE pathogenesis. Consequently, the main focus of the review is to outline the genetic variants in the known associated loci and then to explore the potential functional consequences of the associated variants. We also highlight the genetic overlap of these loci with other autoimmune diseases, which indicates common pathogenic mechanisms. The importance of developing functional assays will be discussed and each of them will be instrumental in furthering our understanding of these associated variants and loci. Finally, we indicate that performing a larger SLE GWAS and applying a more targeted set of methods, such as the ImmunoChip and next generation sequencing methodology, are important for identifying additional loci and enhancing our understanding of the pathogenesis of SLE.

Size-dependent binding of IgA to HepG2, U937, and human mesangial cells

IgA nephropathy (IgAN) is characterized by increased circulating IgA and mesangial IgA deposition. The mechanism of mesangial IgA deposition remains poorly understood in IgAN. In this report, we studied the binding characteristics of serum IgA from patients with IgAN and healthy controls to different cell types, including a liver-cell line (HepG2), a monocytic cell line (U937), and human mesangial cells (HMCs). Jacalin-bound proteins (JBPs) were purified from serum IgA by means of jacalin affinity chromatography. Total IgA concentrations were significantly higher in patients with IgAN than in controls (P <.001). JBPs were further separated by means of size exclusion chromatography, and six pooled fractions with molecular weight ranging from 50 to 1,000 kD were obtained. The concentration of low-molecular-weight (LMW) IgA complexes (150-300 kD) and high-molecular-weight (HMW) IgA complexes (300-1,000 kD) were significantly higher in patients than in healthy controls (P <.001 and.05, respectively). Cultured human mesangial cells bound more IgA of 300 to 610 kD in IgA isolated from patients with IgAN (P <.01). The binding of IgA (LMW and HMW) from patients with IgAN to HepG2 was significantly higher than that of IgA preparations from controls. U937 significantly bound more IgA of 150 to 825 kD in IgA isolated from patients with IgAN (P <.01). Different and distinct binding patterns were observed in the three cell types for IgA with different molecular weights. HMCs bound more HMW than LMW IgA. We noted preferential binding of LMW (150 to 300 kDa) and intermediate (350-710 kDa) IgA to HepG2 than of IgA complexes of more than 710 kDa. U937 mainly bound LMW and intermediate size IgA (150 to 710 kDa) with no binding of IgA with size greater than 710 kD. Our findings suggest that monocytes, hepatocytes, and mesangial cells have unique properties with regard to their binding to different forms of IgA. These characteristic properties may alter the catabolism of circulating IgA and, hence, predispose their deposition in the kidney mesangium in IgAN.

Elimination of soluble 123I-labeled aggregates of IgG in patients with systemic lupus erythematosus. Effect of serum IgG and numbers of erythrocyte complement receptor type 1

Using soluble 123I-labeled aggregates of human IgG (123I-AHIgG) as a probe, we examined the function of the mononuclear phagocyte system in 22 patients with systemic lupus erythematosus (SLE) and 12 healthy controls. In SLE patients, a decreased number of erythrocyte complement receptor type 1 was associated with less binding of 123I-AHIgG to erythrocytes and a faster initial rate of elimination of 123I-AHIgG (mean +/- SEM half-maximal clearance time 5.23 +/- 0.2 minutes, versus 6.58 +/- 0.2 minutes in the controls), with possible spillover of the material outside the mononuclear phagocyte system of the liver and spleen. However, multiple regression analysis showed that serum concentrations of IgG were the most important factor predicting the rate of 123I-AHIgG elimination. IgG concentration may thus reflect immune complex clearance, which in turn, would influence the inflammatory reaction, in SLE.

The rheumatic poison: a survey of some published investigations of the immunopathogenesis of Henoch-Schönlein purpura

Laboratory studies of the pathophysiology of Henoch-Schönlein purpura (HSP) have become more numerous in recent years with the recognition of the disease's links with the mucosal immune system in general and IgA nephropathy in particular. There are weak genetic associations with C4 null phenotypes and with HLA B35 and DR4. Studies of plasma proteins in HSP patients show an increased IgA concentration, activation of the alternative pathway of complement and consumption of factor XIII. High molecular weight (polymeric) IgA has been detected in affected individuals, which some investigators have called "immune complexes". Many patients synthesise an IgA rheumatoid factor in the acute phase, but other autoantibodies are largely absent. In vitro studies of lymphocytes from HSP patients have demonstrated an increased number of IgA-bearing and secreting B-cells, with altered T-cell regulation of antibody synthesis. While these observations point to immune dysregulation--primarily of IgA production--as a consistent feature of acute HSP, there is as yet insufficient information available to allow a consistent theory of pathogenesis to be formulated.

Is Henoch-Schönlein purpura the systemic form of IgA nephropathy?

Despite different clinical features, IgA nephropathy (IgAN) and Henoch-Schönlein purpura (HSP) are indistinguishable by histopathology, leading to the suggestion that HSP is a systemic form of IgAN. This review compares and contrasts the clinical, pathologic, and experimental similarities and differences of these two disorders. Many patients with HSP have minimal extrarenal disease, while up to 30% of patients with IgAN will subsequently have systemic symptoms. Although patients with HSP are usually much younger than those with IgAN, the age distributions often overlap. Both may have recurrent macroscopic hematuria associated with pharyngitis, a similar risk of developing renal insufficiency, and recurrent disease after kidney transplantation. Although the pattern of IgA subclass and complement deposition are similar, monocytic and T lymphocytic infiltrates have been observed only in HSP. Dermal blood vessels of many patients with IgAN have IgA immunofluorescence similar to that in HSP, supporting a systemic process in IgAN. Although the pathogenesis is not clearly understood for either disease, investigations of potential disease mechanisms have revealed striking similarities. These include an up-regulated in vitro IgA immune response, circulating IgA-containing immune complexes and autoantibodies, and decreased Fc receptor-mediated immune clearance. Finally, immunogenetic studies suggest that patients with both conditions inherit a predisposition for disease.

Lymphocyte subpopulations in mesangial IgA glomerulonephritis

Lymphocyte subpopulations in thirty patients with IgA glomerulonephritis and in twenty-four healthy persons were identified using specific monoclonal antibodies. Decreased OKT11+ cells (37.83 +/- 13.34, p less than 0.01) without any changes of OKT4+ cells, but increased OKT8+ cells (25.89 +/- 6.70, p less than 0.01) in patients with IgA glomerulonephritis, as compared to a control group, were found. The OKT4+:OKT8+ ratio was decreased in the patients (2.18 vs. 2.47 for the control group). The monocytes were increased (19.26 +/- 6.63 vs. 2.47 +/- 3.28). No statistically significant correlations between abnormal T cells or monocytes and blood pressure, serum creatinine, erythrocyte sedimentation rate and serum levels of IgA were found. It is concluded that no clear-cut correlation could be demonstrated between in vitro and clinical findings.

Bovine serum albumin (BSA) nephritis in rats. IV. A sequential evaluation of mononuclear phagocyte system (MPS) function

A clearance kinetic study of intravenously administered 125I-labeled aggregated human IgG (125I-AHIgG) from the circulation and its distribution in various organs was performed weekly during the course in a model of experimental immune complex glomerulonephritis which was induced in rats immunized 8 weeks previously with 6 times a week administration of 2 mg of bovine serum albumin (BSA) for 4 weeks from week 8 to 12. The removal rates of the injected 125I-AHIgG from the circulation were retarded in nonproteinuric rats of week 9 and 10, at almost every checked point (p-value was less than 0.01). The clearance in those rats with severe proteinuria returned to the level of the control and of rats in week 8. The distribution of 125I-AHIgG in the liver 4 hours after the administration revealed a considerable decrease in non-overt proteinuric rats of weeks 9, 10, and 11. A similar tendency of decreasing depositions of the radioactivity was shown in the spleen at each 4 hours. In contrast, the uptakes in the kidney and lung at the final week of 12 were larger. Delayed clearance from the circulation and a decreasing handle of the injected macromolecule in the liver and possibly in the spleen may suggest the presence of some impairment of the MPS function in the course of this experimental glomerulonephritis.

Defective in vivo Fc- and C3b-receptor function in IgA nephropathy

Reticuloendothelial function was assessed in 17 patients with IgA nephropathy, using 99Tc-labeled autologous erythrocytes coated with either C3B or IgG. Results were compared with clearances in 14 normal control subjects and with a group of 14 patients with idiopathic mesangial proliferative glomerulonephritis without IgA deposition. The half-life of IgG-coated red cells in the IgA group was 69.8 +/- 32.5 minutes (control 42.2 +/- 9.0 minutes, P = 0.001). The half-life in the non-IgA mesangial proliferative group, 77.9 +/- 31.3 minutes, was not significantly different from that of the IgA patients. Clearance of C3b-coated cells, expressed as the percentage of cells cleared at 30 minutes, was 7.1% +/- 2.6% in the IgA patients, compared with 16.0% +/- 3.2% in control subjects (P less than 0.001) and 13.8% +/- 7.5% in the non-IgA mesangial proliferative group (NS). No statistical correlation was found between clearance results in individual patients and age, sex, weight, serum creatinine, or the severity of disease on clinical and pathological criteria. The severity of the defect in Fc- and C3b-receptor dependent clearances were not statistically correlated in individual patients.