Expression of IgA class switching gene in tonsillar mononuclear cells in patients with IgA nephropathy

The influences of α-hemolytic Streptococcus on class switching and complement activation of human tonsillar cells in IgA nephropathy

While β-hemolytic streptococcus (β-HS) infections are known to predispose patients to acute poststreptococcal glomerulonephritis, there is evidence that implicates α-hemolytic streptococcus (α-HS) in IgA nephropathy (IgAN). The alternative pathway of the complement system has also been implicated in IgAN. We aimed to explore the association between α-HS and complement activation in human tonsillar mononuclear cells (TMCs) in IgAN. In our study, α-HS induced higher IgA levels than IgG levels, while β-HS increased higher IgG levels than IgA levels with more activation-induced cytidine deaminase, in TMCs in the IgAN group. Aberrant IgA1 O-glycosylation levels were higher in IgAN patients with α-HS. C3 and C3b expression was decreased in IgAN patients, but in chronic tonsillitis control patients, the expression decreased only after stimulation with β-HS. Complement factor B and H (CFH) mRNA increased, but the CFH concentration in culture supernatants decreased with α-HS. The percentage of CD19 + CD35 + cells/complement receptor 1 (CR1) decreased with α-HS more than with β-HS, while CD19 + CD21 + cells/complement receptor 2 (CR2) increased more with β-HS than with α-HS. The component nephritis-associated plasmin receptor (NAPlr) of α-HS was not detected on tonsillar or kidney tissues in IgAN patients and was positive on cultured TMCs and mesangial cells. We concluded that α-HS induced the secretion of aberrantly O-glycosylated IgA while decreasing the levels of the inhibitory factor CFH in culture supernatants and CR1 + B cells. These findings provide testable mechanisms that relate α-HS infection to abnormal mucosal responses involving the alternative complement pathway in IgAN.

The Role of Immune Modulation in Pathogenesis of IgA Nephropathy

IgA nephropathy (IgAN) is the most prevalent primary glomerulonephritis worldwide, with diverse clinical manifestations characterized by recurrent gross hematuria or microscopic hematuria, and pathological changes featuring poorly O-galactosylated IgA1 deposition in the glomerular mesangium. Pathogenesis has always been the focus of IgAN studies. After 50 years of research, most scholars agree that IgAN is a group of clinicopathological syndromes with certain common immunopathological characteristics, and multiple mechanisms are involved in its pathogenesis, including immunology, genetics, and environmental or nutritional factors. However, the precise pathogenetic mechanisms have not been fully determined. One hypothesis about the pathogenesis of IgAN suggests that immunological factors are engaged in all aspects of IgAN development and play a critical role. A variety of immune cells (e.g., dendritic cells, NK cells, macrophages, T-lymphocyte subsets, and B-lymphocytes, etc.) and molecules (e.g., IgA receptors, Toll-like receptors, complements, etc.) in innate and adaptive immunity are involved in the pathogenesis of IgAN. Moreover, the abnormality of mucosal immune regulation is the core of IgAN immunopathogenesis. The roles of tonsil immunity or intestinal mucosal immunity, which have received more attention in recent years, are supported by mounting evidence. In this review, we will explore the latest research insights on the role of immune modulation in the pathogenesis of IgAN. With a better understanding of immunopathogenesis of IgAN, emerging therapies will soon become realized.

Expression profile of BAFF in peripheral blood from patients of IgA nephropathy: Correlation with clinical features and Streptococcus pyogenes infection

B cells are critically important for the pathogenesis of IgA nephropathy (IgAN). The present study aimed to investigate the abundance of B cell activating factor (BAFF), which belongs to the tumor necrosis factor superfamily, in the peripheral blood of patients with IgAN. The different forms of BAFF in peripheral blood and its association with clinical features and immunological factors were analyzed. mRNA levels of BAFF and other associated genes in the peripheral blood mononuclear cells (PBMCs) of patients with IgAN and controls were analyzed by quantitative polymerase chain reaction. Cellular BAFF proteins in PBMCs and plasma soluble BAFF proteins were measured by western blot analysis and ELISA, respectively. PBMCs from patients were stimulated with Streptococcus pyogenes (S. pyogenes) ex vivo for the BAFF secretion assay. The data demonstrated that, although mRNA levels of BAFF in PBMC were not significantly increased in patients with IgAN, they were positively associated with those of a proliferation inducing ligand (APRIL), Toll‑like receptor (TLR)2, TLR4 and TLR7. The cellular BAFF protein in PBMCs was not upregulated. Plasma BAFF protein levels in patients with IgAN (n=76) were significantly decreased compared with controls. However, plasma BAFF levels were positively associated with serum creatinine, proteinuria, uric acid and group A Streptococcus infection index in patients with IgAN. In patients with IgAN, plasma BAFF concentrations were markedly higher in those with more severe renal tubular atrophy/interstitial fibrosis and global glomerulosclerosis. Furthermore, BAFF production in PBMCs of patients with IgAN was increased following S. pyogenes stimulation ex vivo. In conclusion, plasma BAFF levels in patients with IgAN were associated with renal function and disease activity. S. pyogenes infection was closely associated with BAFF production in patients with IgAN.

Anti-inflammatory effects of triptolide on IgA nephropathy in rats

IgA nephropathy (IgAN) is the finding of immune deposits predominantly containing polymeric IgA in the glomerular mesangium on renal biopsy. Recently studies show that inflammation may involve in the progression of renal glomerulosclerosis and tubulointerstitial scarring in IgAN. This study was designed to evaluate the renoprotective effect of triptolide on IgAN rat model. IgAN was induced in Sprague-Dawley rats by oral and intravenous immunization with BSA for 12 weeks. Rats were treated with triptolide (200 μg/kg/d intragastrically) from 12 to 28 weeks. At Week 28, the rats was sacrificed, kidneys and blood samples were collected for further analysis. Our data shown that IgAN rat model showed marked deterioration of proteinuria together with higher levels of the urine protein:creatinine ratio compared to the normal control. Animals that underwent intermittent exposure to triptolide treatment exhibited significant improvements in the functional parameters without severe side effects. Rats developing IgAN had profound mesangial proliferation and mesangial expansion, intense and diffuse glomerular IgA deposition, while triptolide treatment significantly attenuated it. We also observed that treatment with triptolide significantly decreases serum levels of IL-1β and IL-18, and may exerted anti-inflammatory effects by down-regulating NLRP3 and TLR4 expression. Our study clearly demonstrated that triptolide prevents IgAN progression via an amelioration of inflammasome-mediated proinflammatory cytokine production, thus brought a light of hope for treatment of IgAN.

The Influence and Role of Microbial Factors in Autoimmune Kidney Diseases: A Systematic Review

A better understanding of the pathophysiology of autoimmune disorders is desired to allow tailored interventions. Despite increased scientific interest a direct pathogenic factor in autoimmune renal disease has been described only in a minority like membranous nephropathy or ANCA-associated vasculitis. Nonetheless the initial step leading to the formation of these antibodies is still obscure. In this review we will focus on the possible role of microbial factors in this context. Staphylococcus aureus may be a direct pathogenetic factor in granulomatosis with polyangiitis (GPA). Chronic bacterial colonization or chronic infections of the upper respiratory tract have been proposed as trigger of IgA vasculitis and IgA nephropathy. Interventions to remove major lymphoid organs, such as tonsillectomy, have shown conflicting results but may be an option in IgA vasculitis. Interestingly no clear clinical benefit despite similar local colonization with bacterial strains has been detected in patients with IgA nephropathy. In systemic lupus erythematosus injection of bacterial lipopolysaccharide induced progressive lupus nephritis in mouse models. The aim of this review is to discuss and summarize the knowledge of microbial antigens in autoimmune renal disease. Novel methods may provide insight into the involvement of microbial antigens in the onset, progression, and prognosis of autoimmune kidney disorders.

Glycans in the immune system and The Altered Glycan Theory of Autoimmunity: a critical review

Herein we will review the role of glycans in the immune system. Specific topics covered include: the glycosylation sites of IgE, IgM, IgD, IgE, IgA, and IgG; how glycans can encode "self" identity by functioning as either danger associated molecular patterns (DAMPs) or self-associated molecular patterns (SAMPs); the role of glycans as markers of protein integrity and age; how the glycocalyx can dictate the migration pattern of immune cells; and how the combination of Fc N-glycans and Ig isotype dictate the effector function of immunoglobulins. We speculate that the latter may be responsible for the well-documented association between alterations of the serum glycome and autoimmunity. Due to technological limitations, the extent of these autoimmune-associated glycan alterations and their role in disease pathophysiology has not been fully elucidated. Thus, we also review the current technologies available for glycan analysis, placing an emphasis on Multiple Reaction Monitoring (MRM), a rapid high-throughput technology that has great potential for glycan biomarker research. Finally, we put forth The Altered Glycan Theory of Autoimmunity, which states that each autoimmune disease will have a unique glycan signature characterized by the site-specific relative abundances of individual glycan structures on immune cells and extracellular proteins, especially the site-specific glycosylation patterns of the different immunoglobulin(Ig) classes and subclasses.

TLR9 and BAFF: their expression in patients with IgA nephropathy

Since it was first described in 1968, immunoglobulin (Ig)A nephropathy (IgAN) has become the most commonly diagnosed form of primary glomerular disease worldwide. A number of reports have shown that toll‑like receptor 9 (TLR9) and B‑cell activating factor (BAFF) may be associated with IgAN; however, sufficient evidence has not yet to be delivered. In the present study, serum levels of BAFF as well as TLR9 mRNA and protein levels in peripheral blood mononuclear cells (PBMCs) were assessed. Expression of TLR9 mRNA in PBMCs was examined by quantitative polymerase chain reaction and the TLR9 protein was determined by western blot analysis. The levels of serum BAFF and IgA1 were determined by specific ELISA. Serum levels of BAFF and IgA1 as well as levels of TLR9 mRNA and protein in PMBCs were significantly higher in patients with IgAN compared with patients with minimal glomerular abnormalities (P<0.05, P<0.01, P<0.01 and P<0.01, respectively) and normal controls (P<0.01, P<0.01, P<0.05 and P<0.01, respectively). A correlation and regression analysis was performed to determine the pathogenesis of IgAN. In patients with IgAN, serum levels of BAFF were positively correlated with IgA1 levels (rp, 0.515; P<0.01) and mesangial IgA deposition density (rp, 0.746; P<0.01). Expression levels of TLR9 protein in PBMCs of IgAN patients were positively correlated with levels of serum BAFF (rp, 0.444; P<0.05) and IgA1 (rp, 0.633; P<0.01). These results suggested that overexpression of TLR9 mRNA and protein in PBMCs and elevated levels of serum BAFF may be associated with overexpression of serum IgA1, and, furthermore, may have a role in the development of IgAN.

Th1/Th2 polarization in tonsillar lymphocyte form patients with IgA nephropathy

Imbalance of Th1/Th2 pro-inflammatory cytokines plays an important role in the development and progression of IgA nephropathy (IgAN). Clinical development and exacerbation of IgAN are frequently preceded by episodes of upper respiratory tract infection, and palatine tonsils represent the predominant immunocompetent tissue of the upper respiratory tract. This study examined tonsillar lymphocytes of IgAN who suffered from tonsillitis (n = 22), and using tonsils derived from patients with chronic tonsillitis (n = 24) but without renal disease as a control. We identified a polarization toward Th2 response in tonsils of IgAN patients. TH0 cells are differentially mobilized during contact sensitization and by adjuvants such as lipopolysaccharide (LPS) that induce T-helper type 1 (Th1) responses, or α-hemolytic streptococcus (HS) that induces T-helper type 2 (Th2) responses. Th1:Th2 ratio is correlated with proteinuria and renal pathologic changes in IgAN group. Our study suggests that IgAN is associated with the change in Th1/Th2 balance in favor of Th2 lymphocytes.

Activation of the interleukin-4/signal transducer and activator of transcription 6 signaling pathway and homeodomain-interacting protein kinase 2 production by tonsillar mononuclear cells in IgA nephropathy

BACKGROUND/AIM

Clinical development and exacerbation of IgA nephropathy (IgAN) are frequently preceded by episodes of upper respiratory tract infection such as tonsillitis. This study aimed to determine the role of the interleukin-4 (IL-4)/signal transducer and activator of transcription 6 (STAT6) signaling pathway and homeodomain-interacting protein kinase 2 (HIPK2) in aberrant IgA1 O-glycosylation production, and identify potential therapeutic targets in IgAN.

METHODS

Expression levels of IL-4, STAT6, core1β1,3-galactosyltransferase (C1GALT1C1), core1β3GalT-specific molecular chaperone (Cosmc) and HIPK2 in tonsil components were examined by immunohistochemical and immunofluorescence staining. Lymphocytes isolated from 22 patients with IgAN and 24 patients with chronic tonsillitis (CT) as controls were cultured for 72 h with or without IL-4, lipopolysaccharide (LPS) and α-hemolytic streptococcus (HS) stimulation. Expression levels of STAT6, C1GALT1C1, Cosmc, HIPK2-mRNA and protein were measured by real-time PCR and Western blot analysis, respectively. The concentration of IgA1 and level of O-glycosylation were determined by ELISA and Vicia villosa (VV) lectin-binding assay. To determine the contribution of HIPK2 in IgA secretion and O-glycosylation, cells were subjected to experiments for evaluation of HIPK2 silencing by Hipk2-siRNA transfection.

RESULTS

The IL-4/STAT6 signaling pathway was highly activated in all tonsil tissues (including the germinal center and tonsillar crypt epithelium) of IgAN patients, but the gene or protein expression of β1,3-Gal transferase (C1GALT1) and COSMC decreased significantly in patients with IgAN in comparison with those with CT. Hipk2 production in the tonsils derived from IgAN patients was significantly higher than that of CT patients. HIPK2-mRNA expression significantly negatively correlated with renal function as expressed by the estimated glomerular filtration rate, and also significantly positively correlated with daily proteinuria. The level of IL-4, STAT6 and HIPK2 were closely related with Lee's pathological grading system. The levels of mRNA and protein encoding STAT6 and Hipk2 in cells coincubated with IL-4, LPS and HS were significantly higher than those in the controls without stimulation; however, in the IgAN group the levels of mRNA and protein encoding C1GALT1 and Cosmc were significantly lower compared to the controls. IgA1 concentrations of supernatants in IgAN patients were remarkably higher under conditions of external stimulation. As expected, the optical density value of VV lectin binding to IgA1 increased after external stimulation in the IgAN group. By siRNA transfection, our results clearly indicate that Hipk2 negatively regulates C1GALT1 and Cosmc expression. Importantly, HIPK2-siRNA attenuates the aberrant glycosylation of IgA1 secretion.

CONCLUSION

We identified and confirmed that activation of the IL-4/STAT6 signaling pathway has a crucial role in aberrant glycosylation of IgA1 secretion. HIPK2, a protein kinase previously unrecognized in kidney disease, may mediate the glycosylation of IgA1. We believe that HIPK2 could be a new therapeutic target for IgAN, especially as protein kinases are 'drugable' targets.