Genetics of IgA nephrology: risks, mechanisms, and therapeutic targets.

IgA nephropathy (IgAN) is a genetically complex multifactorial trait. Over the past decade, population-based genome-wide association studies (GWAS) have identified more than 30 IgAN risk loci, providing novel perspectives on both the epidemiology of the disease and its underlying molecular mechanisms. In addition, the association between IgAN and galactose-deficient IgA1 (Gd-IgA1) presented another avenue for genetic exploration due to the heritability of the elevated serum Gd-IgA1 levels. These endeavors also yielded and enabled refinement of polygenic risk scores, which may help identify specific groups of individuals at significantly increased risks, leading to stratifications of medical treatments. In this review, we aim to explore the existing evidence for genetic causation in IgAN. We summarize the state of genetic research in IgAN and how it has led to the reformulation of the new pathogenesis model and novel therapeutic targets.

Porphyromonas gingivalis infection in the oral cavity is associated with elevated galactose-deficient IgA1 and increased nephritis severity in IgA nephropathy.

BACKGROUND: The relationship between the major periodontal bacteria, Porphyromonas gingivalis, and the pathogenesis of IgA nephropathy (IgAN)-particularly with respect to galactose-deficient IgA1 (Gd-IgA1)-has not been fully elucidated. METHODS: Saliva samples from 30 IgAN patients and 44 patients with chronic kidney disease (CKD) were subjected to analysis of P. gingivalis status via polymerase chain reaction using a set of P. gingivalis-specific primers. The associations between P. gingivalis presence and clinical parameters, including plasma Gd-IgA1, were analyzed in each group. RESULTS: Compared with the CKD group, the IgAN group demonstrated significantly higher plasma Gd-IgA1 levels (p < 0.05). Compared with the P. gingivalis-negative subgroup, the P. gingivalis-positive subgroup exhibited significantly higher plasma Gd-IgA1 levels in both IgAN and CKD patients (p < 0.05). Additionally, among IgAN patients, the P. gingivalis-positive subgroup displayed significantly higher plasma Gd-IgA1 and urine protein levels, compared with the P. gingivalis-negative subgroup (p < 0.05). With respect to renal biopsy findings, the frequencies of segmental glomerulosclerosis and tubular atrophy/interstitial fibrosis were significantly greater in the P. gingivalis-positive subgroup than in the P. gingivalis-negative subgroup, according to the Oxford classification of IgAN (p < 0.05). CONCLUSION: Our findings suggest an association between the presence of P. gingivalis in the oral cavity and the pathogenesis of IgAN, mediated by increased levels of Gd-IgA1.

Pediatric IgA-Dominant Infection-Related Glomerulonephritis.

The concept of infection-related glomerulonephritis (IRGN) has been introduced as adults diagnosed with glomerulonephritis often have coexisting active infections. Furthermore, IgA-dominant IRGN is associated with staphylococcal infections in adults with comorbidities, which often progress to end-stage renal disease. Little is known about IgA-dominant IRGN in children, and no consensus for a management strategy of this condition has been reached. We describe the case of a 9-year-old boy with IgA-dominant IRGN that was diagnosed using specific staining for nephritis-associated plasmin receptor (NAPlr)/plasmin activity and galactose-deficient IgA1 (Gd-IgA1), a marker of IgA nephropathy. The patient was successfully treated using a combination of prednisolone, mizoribine (an immunosuppressive drug), and lisinopril (an angiotensin-converting enzyme inhibitor) and three courses of methylprednisolone pulse therapy. The patient was admitted to our hospital with generalized edema, gross hematuria, proteinuria, hypertension, and renal dysfunction. Hypocomplementemia contributed to a diagnosis of IRGN, although the causative organism was unknown. A renal biopsy performed when the patient presented with nephrotic syndrome showed IgA deposition, positive staining for NAPlr, and negative staining for Gd-IgA1, in addition to findings consistent with IRGN, leading to a pathologic diagnosis of IgA-dominant IRGN. The histological staining for NAPlr/plasmin activity and Gd-IgA1, together with clinical symptoms, could be helpful for diagnosing IgA-dominant IRGN. Our findings indicate that otherwise healthy children can also develop IgA-dominant IRGN. Therefore, early diagnosis and aggressive treatment should be considered when IgA-dominant IRGN is suspected to avoid the possibility of incomplete recovery of renal function.

Galactose-Deficient IgA1 B cells in the Circulation of IgA Nephropathy Patients Carry Preferentially Lambda Light Chains and Mucosal Homing Receptors.

BACKGROUND: IgA nephropathy (IgAN) primary glomerulonephritis is characterized by the deposition of circulating immune complexes composed of polymeric IgA1 molecules with altered O-glycans (Gd-IgA1) and anti-glycan antibodies in the kidney mesangium. The mesangial IgA deposits and serum IgA1 contain predominantly λ light (L) chains, but the nature and origin of such IgA remains enigmatic. METHODS: We analyzed λ L chain expression in peripheral blood B cells of 30 IgAN patients, 30 healthy controls (HCs), and 18 membranous nephropathy patients selected as disease controls (non-IgAN). RESULTS: In comparison to HCs and non-IgAN patients, peripheral blood surface/membrane bound (mb)-Gd-IgA1+ cells from IgAN patients express predominantly λ L chains. In contrast, total mb-IgA+, mb-IgG+, and mb-IgM+ cells were preferentially positive for kappa (κ) L chains, in all analyzed groups. Although minor in comparison to κ L chains, λ L chain subsets of mb-IgG+, mb-IgM+, and mb-IgA+ cells were significantly enriched in IgAN patients in comparison to non-IgAN patients and/or HCs. In contrast to HCs, the peripheral blood of IgAN patients was enriched with λ+ mb-Gd-IgA1+, CCR10+, and CCR9+ cells, which preferentially home to the upper respiratory and digestive tracts. Furthermore, we observed that mb-Gd-IgA1+ cell populations comprise more CD138+ cells and plasmablasts (CD38+) in comparison to total mb-IgA+ cells. CONCLUSIONS: Peripheral blood of IgAN patients is enriched with migratory λ+ mb-Gd-IgA1+ B cells, with the potential to home to mucosal sites where Gd-IgA1 could be produced during local respiratory or digestive tract infections.

Particulate matter of air pollution may increase risk of kidney failure in IgA nephropathy.

IgA nephropathy (IgAN) is characterized by deposition of galactose-deficient IgA1 (Gd-IgA1) in glomerular mesangium associated with mucosal immune disorders. Since environmental pollution has been associated with the progression of chronic kidney disease in the general population, we specifically investigated the influence of exposure to fine particulate matter less than 2.5 µm in diameter (PM2.5) on IgAN progression. Patients with biopsy-proven primary IgAN were recruited from seven Chinese kidney centers. PM2.5 exposure from 1998 to 2016 was derived from satellite aerosol optical depth data and a total of 1,979 patients with IgAN, including 994 males were enrolled. The PM2.5 exposure levels for patients from different provinces varied but, in general, the PM2.5 exposure levels among patients from the north were higher than those among patients from the south. The severity of PM2.5 exposure in different regions was correlated with regional kidney failure burden. In addition, each 10 µg/m3 increase in annual average concentration of PM2.5 exposure before study entry (Hazard Ratio, 1.14; 95% confidence interval, 1.06-1.22) or time-varying PM2.5 exposure after study entry (1.10; 1.01-1.18) were associated with increased kidney failure risk after adjustment for age, gender, estimated glomerular filtration rate, urine protein, uric acid, hemoglobin, mean arterial pressure, Oxford classification, glucocorticoid and renin-angiotensin system blocker therapy. The associations were robust when the time period, risk factors of cardiovascular diseases or city size were further adjusted on the basis of the above model. Thus, our results suggest that PM2.5 is an independent risk factor for kidney failure in patients with IgAN, but these findings will require validation in more diverse populations and other geographic regions.

Experimental evidence of pathogenic role of IgG autoantibodies in IgA nephropathy.

BACKGROUND: IgA nephropathy is thought to be an autoimmune disease wherein galactose-deficient IgA1 (Gd-IgA1) is recognized by IgG autoantibodies, resulting in formation and renal accumulation of nephritogenic immune complexes. Although this hypothesis is supported by recent findings that, in renal immunodeposits of IgA nephropathy patients, IgG is enriched for Gd-IgA1-specific autoantibodies, experimental proof is still lacking. METHODS: IgG isolated from sera of IgA nephropathy patients or produced as a recombinant IgG (rIgG) was mixed with human Gd-IgA1 to form immune complexes. IgG from healthy individuals served as a control. Nude and SCID mice were injected with human IgG and Gd-IgA1, in immune complexes or individually, and their presence in kidneys was ascertained by immunofluorescence. Pathologic changes in the glomeruli were evaluated by quantitative morphometry and exploratory transcriptomic profiling was performed by RNA-Seq. RESULTS: Immunodeficient mice injected with Gd-IgA1 mixed with IgG autoantibodies from patients with IgA nephropathy, but not Gd-IgA1 mixed with IgG from healthy individuals, displayed IgA, IgG, and mouse complement C3 glomerular deposits and mesangioproliferative glomerular injury with hematuria and proteinuria. Un-complexed Gd-IgA1 or IgG did not induce pathological changes. Moreover, Gd-IgA1-rIgG immune complexes injected into immunodeficient mice induced histopathological changes characteristic of human disease. Exploratory transcriptome profiling of mouse kidney tissues indicated that these immune complexes altered gene expression of multiple pathways, in concordance with the changes observed in kidney biopsies of patients with IgA nephropathy. CONCLUSIONS: This study provides the first in vivo evidence for a pathogenic role of IgG autoantibodies specific for Gd-IgA1 in the pathogenesis of IgA nephropathy.

Associations of ABO blood type and galactose-deficient immunoglobulin A1 with adverse outcomes in patients with IgA nephropathy.

BACKGROUND: Both ABO blood group antigens and pathogenic immunoglobulin A1 (IgA1) in patients with IgA nephropathy (IgAN) are influenced by modifications of N-acetylgalactosamine and galactose. The purpose of this study was to assess whether ABO blood type is associated with galactose-deficient IgA1 (Gd-IgA1) in the progression of kidney disease in patients with IgAN. METHODS: We enrolled 1313 IgAN patients with a median of 44 months follow-up and measured the plasma Gd-IgA1 levels. Multivariate Cox regression models were used to estimate the association between all variables and adverse outcomes. Using the propensity score matching method, 718 IgAN patients with blood type either A or B were selected, and their data were used to assess the association of blood type and Gd-IgA1/serum complement 3 (sC3) with outcomes. RESULTS: We found that the risk of adverse outcomes was significantly higher in patients with blood type A than in those with type B (hazard ratio = 1.82, 95% confidence interval 1.23-2.71; P = 0.003) after multivariate adjustment. The Gd-IgA1 levels showed trends similar to the multivariate-adjusted event-free curves for the blood types. However, this higher risk of adverse outcomes in type A than in type B patients was no longer significant after the addition of Gd-IgA1/sC3 to the model. CONCLUSIONS: IgAN patients with blood type A had a higher risk of adverse outcomes than those with type B, and this risk was associated with Gd-IgA1/sC3. Thus, the ABO blood type may provide a reference for the prognostic factors for individuals with IgAN.

Utility of glomerular Gd-IgA1 staining for indistinguishable cases of IgA nephropathy or Alport syndrome.

BACKGROUND: Pathological findings in Alport syndrome frequently show mesangial proliferation and sometimes incidental IgA deposition, in addition to unique glomerular basement membrane (GBM) changes including thin basement membrane and/or lamellation. However, similar GBM abnormalities are also often observed in IgA nephropathy. Both diseases are also known to show hematuria, proteinuria, and sometimes macrohematuria when associated with viral infection. Therefore, it can be difficult to make a differential diagnosis, even based on clinical and pathological findings. Some recent articles demonstrated that galactose-deficient IgA1 (Gd-IgA1)-specific monoclonal antibody (KM55) could potentially enable incidental IgA deposition to be distinguished from IgA nephropathy. METHODS: We performed comprehensive gene screening and glomerular Gd-IgA1 and type IV collagen α5 chain immunostaining for five cases with both IgA deposition and GBM changes to confirm that Gd-IgA1 can help to distinguish these two diseases. RESULTS: Four of the cases were genetically diagnosed with Alport syndrome (Cases 1-4) and one was IgA nephropathy with massive GBM changes, which had a negative gene test result (Case 5). In Cases 1-4, glomerular Gd-IgA1 deposition was not detected, although there was positivity for IgA in the mesangial area. In Case 5, glomerular Gd-IgA1 deposition was observed. CONCLUSION: Gd-IgA1 expression analysis could clearly differentiate these two disorders. This approach can be applied to identify these two diseases showing identical clinical and pathological findings.

Serum levels of galactose-deficient IgA1 in Chinese children with IgA nephropathy, IgA vasculitis with nephritis, and IgA vasculitis.

OBJECTIVE: IgA nephropathy (IgAN) and IgA vasculitis with nephritis (IgAV-N) are related diseases. Galactose-deficient IgA1 (Gd-IgA1) plays an important role in the pathology of IgAV-N and IgAN, so we aim to compare the serum levels of Gd-IgA1 in Chinese pediatric patients with IgAN, IgAV-N, and IgAV. METHODS: We retrospectively enrolled 52 patients with IgAN, 57 patients with IgAV-N, 26 patients with IgAV, and 40 healthy children. The serum levels of Gd-IgA1 were measured at the time of biopsy using a lectin-based ELISA method. RESULTS: Gd-IgA1 levels in IgAV-N patients and IgAN patients were higher than in healthy controls (303.94 ± 39.37 U/ml, 314.91 ± 47.79 U/ml vs. 273.57 ± 48.29 U/ml, P < 0.001), and Gd-IgA1 levels in IgAV-N patients were higher than in IgAV patients (303.94 ± 39/ml vs. 286. 21 ± 38.81 U/ml, P = 0.059), but the latter result is not statistically significant. The Gd-IgA1 levels in IgAV patients were comparable with those in healthy controls (286.21 ± 38.81 U/ml vs. 273.57 ± 48.29 U/ml, P = 0.267). Among the four groups, we did not observe significant correlations of Gd-IgA1 levels with eGFR, proteinuria, or the MEST-C score. CONCLUSION: Serum Gd-IgA1 maybe involved in the pathogenesis of the IgAV-N and IgAN. However, we found no statistically significant correlation between Gd-IgA1 levels and clinical and pathological features.

Glomerulonephritis with severe nephrotic syndrome induced by immune complexes composed of galactose-deficient IgA1 in primary Sjögren's syndrome: a case report.

BACKGROUND: Primary Sjögren's syndrome (pSS) is an auto-immune disease characterized by sialadenitis and dacryoadenitis with lymphoplasmacytic cell infiltration. In pSS, not only sicca symptoms, but also extra-glandular involvement induced by immune abnormalities based on pSS occurs. Renal involvement is one such important life-threatening extra-glandular involvement. Although the aberrant glycosylated IgA in pSS as a product of over-activated B cells is a risk factor of renal involvement, its association has not been clarified. Here we report a case of glomerulonephritis (GN) induced by immune complexes (IC) composed of galactose-deficient IgA1 (Gd-IgA1) in a patient with pSS. CASE PRESENTATION: A 48-year-old Japanese woman with pSS was admitted to our hospital because of a two-month history of nephrotic syndrome. Seven years before she had been diagnosed with pSS from keratoconjunctivitis sicca, elevation of serum anti-Ro/SSA antibody titer and lymphoplasmacytic cell infiltration around salivary ducts of the small salivary glands. Renal biopsy revealed diffuse bubbling appearance in glomerular basement membrane (GBM) with scarce mesangial proliferation. Immunofluorescence showed granular IgA, C3 and Gd-IgA1 staining of GBM. Light chain staining showed no monoclonality. Electron microscopy showed electron dense deposits mainly in the intra-membranous and paramesangial areas and slightly in the subepithelial area. Additional serum analysis confirmed elevation of Gd-IgA1 (13.5 µg/mL), which was comparable with that seen in IgA nephropathy, and qualitative enzyme-linked immunosorbent assay of IgA-containing circulating immune complex (IgA-CIC) was positive. Thus, we diagnosed GN induced by IC composed of Gd-IgA1. Furthermore, retrospectively performed immunofluorescence of the small salivary gland evaluated at the diagnosis of pSS showed positive Gd-IgA1 staining of infiltrating lymphoplasmacytic cells. Therefore, we concluded that Gd-IgA1 produced by over-activated B cells in pSS formed circulating IC and thereby induced GN. After induction therapy with high dose prednisolone and mycophenolate mofetil, the nephrotic syndrome remitted within 3 weeks, the serum Gd-IgA1 level decreased to the normal range (3.8 µg/mL), and serum IgA-CIC disappeared in the 6th month after induction therapy. CONCLUSIONS: Our findings clearly demonstrate an association between aberrant glycosylated IgA and the renal involvement seen in pSS, thereby helping to clarify the renal significance of aberrant glycosylated IgA in pSS.

ST6Gal1 is up-regulated and associated with aberrant IgA1 glycosylation in IgA nephropathy: An integrated analysis of the transcriptome.

Galactose-deficient IgA1 (Gd-IgA1) plays a crucial role in the development of Immunoglobulin A nephropathy (IgAN), however, the underlying pathogenic mechanisms driving Gd-IgA1 production in B cells are not well understood. In this study, RNA-seq analysis identified 337 down-regulated and 405 up-regulated genes in B cells from 17 patients with IgAN and 6 healthy controls. Among them, ST6Gal1, which was associated with IgAN in a previous genome-wide association study (GWAS), was up-regulated in IgAN and significantly positive correlated with elevated Gd-IgA1. In addition, we identified increased plasma ST6Gal1 levels in 100 patients with IgAN, which were associated with higher levels of proteinuria, plasma IgA, Gd-IgA1 levels, greater degrees of systemic complement activation including C3a, Bb, C4d, MAC and a lower proportion classified as C2 grade (crescent proportion ≥25%). Interesting, in vitro, recombinant ST6Gal1 (rST6Gal1) exposure reduced the production of Gd-IgA1 in cultured peripheral blood mononuclear cells from IgAN patients. rST6Gal1 stimuli also increased expression of C1GALT1, which were well-known proportional to the decrease in galactose deficiency of IgA1. In conclusions, we identified increased plasma ST6Gal1 levels and the association of ST6Gal1 with disease severity of IgAN. Additionally, rST6Gal1 administration in vitro increased expression of C1GALT1 and reduced the production of Gd-IgA1.

TLR9 activation induces aberrant IgA glycosylation via APRIL- and IL-6-mediated pathways in IgA nephropathy.

Galactose-deficient IgA1 (Gd-IgA1) plays a crucial role in the development of IgA nephropathy (IgAN). However, the pathogenic mechanisms driving Gd-IgA1 production have not been fully elucidated. Innate-immune activation via Toll-like receptor 9 (TLR9) is known to be involved in Gd-IgA1 production. A proliferation inducing ligand (APRIL) and IL-6 are also known to enhance Gd-IgA1 synthesis in IgAN. With this as background, we investigated how TLR9 activation in IgA secreting cells results in overproduction of nephritogenic IgA in the IgAN-prone ddY mouse and in human IgA1-secreting cells. Injection of the TLR9 ligand CpG-oligonucleotides increased production of aberrantly glycosylated IgA and IgG-IgA immune complexes in ddY mice that, in turn, exacerbated kidney injury. CpG-oligonucleotide-stimulated mice had elevated serum levels of APRIL that correlated with those of aberrantly glycosylated IgA and IgG-IgA immune complexes. In vitro, TLR9 activation enhanced production of the nephritogenic IgA as well as APRIL and IL-6 in splenocytes of ddY mice and in human IgA1-secreting cells. However, siRNA knock-down of APRIL completely suppressed overproduction of Gd-IgA1 induced by IL-6. Neutralization of IL-6 decreased CpG-oligonucleotide-induced overproduction of Gd-IgA1. Furthermore, APRIL and IL-6 pathways each independently mediated TLR9-induced overproduction of Gd-IgA1. Thus, TLR9 activation enhanced synthesis of aberrantly glycosylated IgA that, in a mouse model of IgAN, further enhanced kidney injury. Hence, APRIL and IL-6 synergistically, as well as independently, enhance synthesis of Gd-IgA1.

Immunostaining of galactose-deficient IgA1 by KM55 is not specific for immunoglobulin A nephropathy.

BACKGROUND: Immunoglobulin A nephropathy (IgAN nephropathy, IgAN) is named for the renal pathological features of IgA-dominant immunoglobulin deposition. IgA deposits, however, may also occur in other diseases, from liver disease and inflammation to chronic infections and tumors. Now increasing studies have suggested that galactose-deficient IgA1 (Gd-IgA1) plays a critical role in the pathogenesis of IgAN. This study aims to investigate whether the Gd-IgA1-specific antibody KM55 contributes to differentiating primary IgAN from other diseases with IgA deposits. METHODS: In this retrospective study, we enrolled 100 Chinese patients with IgA deposits in renal biopsies, including IgAN(n = 40), IgAN with hepatitis B virus antigen deposits(n = 14), IgA vasculitis(n = 16), lupus nephritis(n = 11), incidental IgA deposits(n = 13) and negative controls(n = 6). Double immunostaining of Gd-IgA1 and IgA was performed in all biopsies. RESULTS: There were similar patterns of Gd-IgA1 deposition in primary IgAN, IgA vasculitis, and IgAN with hepatitis B virus antigen deposits. Gd-IgA1 staining could also be seen in patients with lupus nephritis and incidental IgA deposits, but the intensity was significantly lower than IgAN, and the optimal cutoff was 2+ staining for differential diagnosis. Every increase in KM55 staining intensity of 1+ was associated with an increase in the odds of primary IgAN (OR: 4.399; 95% CI: 1.725-11.216). CONCLUSIONS: Immunostaining for Gd-IgA1 by KM55 is not specific for IgA nephropathy, but weak or negative staining may favor incidental IgA deposits.

Case report on mesangial proliferative glomerulonephritis with multicentric Castleman's disease: Approach to the onset mechanism of immunoglobulin A nephropathy.

Galactose-deficient immunoglobulin A1 (Gd-IgA1) was recently identified as a critical effector molecule in the pathogenesis of IgA nephropathy (IgAN). Gd-IgA1 is produced by the mucosal immune system. IgAN is thought to develop because of the deposition of a circulating immune-complex containing Gd-IgA1 in the kidney. Multicentric Castleman's disease (MCD) is a rare non-neoplastic lymphoproliferative disorder. As an etiology model, hypercytokinemia, including increased levels of interleukin-6, is the primary pathogenesis of many MCD cases. Here, we present two cases of mesangial proliferative glomerulonephritis with MCD. According to renal biopsy findings, one was diagnosed with non-IgAN and the other with IgAN. Surprisingly, in both cases, Gd-IgA1 was produced by plasma cells in the lymph nodes, suggesting that Gd-IgA1 production alone does not cause IgAN; rather, it may be produced without induction by mucosal immunity. Our findings demonstrate the diversity of the development of IgAN and help to reconsider the onset mechanism of IgAN.

Plasma galactose-deficient immunoglobulin A1 and loss of kidney function in patients with immunoglobulin A vasculitis nephritis.

BACKGROUND: Immunoglobulin A (IgA) vasculitis nephritis (IgAV-N) is the most common secondary IgA nephropathy (IgAN). Many studies have demonstrated that galactose-deficient IgA1 (Gd-IgA1) in the IgA1 hinge region is associated with the development and also progression of primary IgAN. In this study, we aimed to evaluate the roles of Gd-IgA1 in kidney disease progression in a large Chinese cohort of IgAV-N patients. METHODS: This cohort study enrolled 112 patients with IgAV-N, 15 patients with IgA vasculitis (IgAV) without kidney involvement and 108 patients with IgAN. Plasma IgA1 and Gd-IgA1 levels at kidney biopsy were measured by enzyme-linked immunosorbent assay. The primary endpoint was a 30% decline in estimated glomerular filtration rate or end-stage renal disease or death. RESULTS: The levels of Gd-IgA1 in IgAV-N and IgAN patients were higher than in healthy controls (mean ± SD, 302.86 ± 54.93 U/mL versus 303.16 ± 59.43 U/mL versus 281.30 ± 43.74 U/mL, respectively; P = 0.047), as well as compared with those with IgAV without kidney involvement (272.65 ± 53.14 U/mL; P = 0.036). After adjusting clinical data, higher levels of Gd-IgA1 were found to be independently associated with a greater risk for kidney failure [hazard ratio (HR) = 1.703 per 1 SD, 95% confidence interval (CI) 1.233-2.352; P = 0.001]. Compared with the first Gd-IgA1 quartile group (as reference), the fourth Gd-IgA1 quartile group retained a predictive value for poor renal outcome (HR = 3.740, 95% CI 1.204-11.619; P = 0.023). CONCLUSIONS: These data indicate that Gd-IgA1 levels were similarly elevated in adult patients with IgAN and those with IgAV-N. Moreover, increased Gd-IgA1 levels were associated with both the development and progression of IgAV-N, as observed in IgAN.

C1GALT1 expression is associated with galactosylation of IgA1 in peripheral B lymphocyte in immunoglobulin a nephropathy.

BACKGROUND: More and more studies demonstrated that genetic variation at C1GALT1 influences Gd-IgA1 level in IgAN. However, whether the expression of ß1, 3-galactosyltransferase (ß1, 3Gal-T) was influenced may provide insights into how Gd-IgA1 levels are controlled in IgAN. METHODS: Thirty IgAN patients diagnosed in Tianjin Medical University General Hospital from April to September 2018 and 30 healthy volunteers whose age and gender matched with patients were enrolled in this study. Total Gd-IgA1 levels in plasma were determined by ELISA and C1GALT1 levels were determined by RT-PCR. Four databases (PubMed, EMBASE, CNKI, WanFang Medical Network) were searched to identify eligible studies that evaluated a difference in the expression of C1GALT1 in IgAN patients compared with total controls (non-IgAN and health controls). The C1GALT1C1 expression levels, which was indispensable to ß1, 3Gal-T of IgA1, was also been compared. RESULTS: Gd-IgA1 levels were remarkable higher in IgAN patients compared with healthy control. The expression levels of C1GALT1 gene were remarkably down-regulated in IgAN patients compared with healthy control. And the mRNA level of C1GALT1 was inversely correlated to Gd-IgA1 levels. In meta-analysis, six articles including 316 participants that analyzed the expression of ß1, 3Gal-T were met inclusion criteria. There was no significant difference in the expression of C1GALT1 between IgAN patients compared with controls. And we found patients with IgAN had lower levels of C1GALT1 gene expression in the B cells compared to controls. The C1GALT1C1 levels in the IgAN patients were not different from the levels in the control group, which were unchanged no matter according to different ethnic population, different control group and different cell source. Two studies including 46 persons compared enzymatic activity of ß1, 3Gal-T in B cells, and the result showed the ß1, 3Gal-T activity was decreased in B cells. CONCLUSIONS: We found expression levels of C1GALT1 were remarkably downregulated in IgAN patients and negatively correlated with higher levels of Gd-IgA1. Subsequent meta-analysis validated the low expression and activity of ß1, 3Gal-T in B cells in patients with IgAN. However, there was no apparent disparity in the aspect of C1GALT1C1 expression between IgAN and control groups.

IgA nephropathy: A brief review.

IgA nephropathy is a lifelong disease that is the most common primary glomerulopathy worldwide. It has a complicated and incompletely understood pathogenesis that is theorized as a four 'hit' process involving an improperly produced IgA. While it has a variety of histologic appearances, it is diagnosed by the presence of bright IgA deposits within the mesangium as seen on immunofluorescence and mesangial hypercellularity by light microscopy. This brief review explains the varied histologic features that are important in the diagnosis of IgA nephropathy and the calculation of the MEST-C score that was first introduced by the 2009 Oxford Classification working group.

Helicobacter pylori infection is associated with elevated galactose-deficient IgA1 in IgA nephropathy.

Background: Mucosal immunity plays an important role in the pathogenesis of IgA nephropathy (IgAN). This study aimed to investigate if infection of Helicobacter pylori (H. pylori), a common bacteria in the gastrointestinal tract, associated with IgAN.Methods: This study included 261 patients with IgAN and 46 healthy controls. Clinical information and plasma samples were collected from patients and healthy controls. H. pylori infection was confirmed by western blot. Plasma IgA1 and galactose-deficient IgA1 (Gd-IgA1) levels were detected by specific enzyme-linked immunosorbent assay.Results: Total H. pylori infection rates showed no statistical differences between IgAN patients and healthy controls, but the infection rates of type I H. pylori in IgAN patients were significantly higher than those in healthy controls (44.4 vs. 28.3%, p = 0.040). Compared with uninfected patients, the systolic blood pressure, 24-h proteinuria, and blood urea nitrogen levels were significantly higher in patients with H. pylori infection (126.0 ± 15.5 vs. 119.6 ± 14.5 mmHg, p = 0.010; 1.8 ± 2.7 vs. 1.2 ± 1.4 g/24h, p = 0.013; 7.9 ± 5.4 vs. 6.7 ± 3.9 µmol/L, p = 0.042), especially in patients with type I infection (126.5 ± 15.4 vs. 119.6 ± 14.5 mmHg, p = 0.002; 1.9 ± 2.9 vs. 1.2 ± 1.4 g/24 h, p = 0.033; 8.1 ± 5.6 vs. 6.7 ± 3.9 µmol/L, p = 0.041). Similarly, patients with IgAN and type I H. pylori infection showed higher plasma Gd-IgA1 levels than uninfected patients (5.5 ± 2.2 vs. 4.5 ± 2.2 µg/mL, p = 0.037).Conclusions: Virulent type I H. pylori infection is more common in patients with IgAN. Patients with IgAN and type I H. pylori infection showed lower renal function and higher underglycosylation of plasma IgA1.

Comprehensive analysis of aberrantly expressed profiles of mRNA and its relationship with serum galactose-deficient IgA1 level in IgA nephropathy.

BACKGROUND: Immunoglobulin A nephropathy (IgAN) is the leading cause of end-stage kidney disease. Previous mRNA microarray profiling studies of IgAN revealed inconsistent data. We sought to identify the aberrantly expressed genes and biological pathways by integrating IgAN gene expression datasets in blood cells and performing systematically experimental validation. We also explored the relationship between target genes and galactose-deficient IgA1 (Gd-IgA1) in IgAN. METHODS: We retrieved Gene Expression Omnibus (GEO) datasets of IgAN. Gene Ontology (GO) enrichment and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses were used for functional analysis. Deep sequencing on RNA isolated from B cells was used for microarray validation. The relationship between target mRNA expressions and Gd-IgA1 levels in serum were also studied. RESULTS: Three studies with microarray expression profiling datasets met our inclusion criteria. We identified 655 dyregulated genes, including 319 up-regulated and 336 down-regulated genes in three GEO datasets with a total of 35 patients of IgAN and 19 healthy controls. Based on biological process in GO term, these dyregulated genes are mainly related to pentose-phosphate shunt, non-oxidative branch, post-embryonic camera-type eye development and leukocyte activation. KEGG pathway analysis of microarray data revealed that these aberrantly expressed genes were enriched in human T-cell leukemia virus 1 infection, proteoglycans in cancer, intestinal immune network for IgA production and autophagy. We further performed deep sequencing on mRNAs isolated from B cells of an independent set of five patients with IgAN and three healthy persons with the same clinical and demographic characteristics. Seventy-seven genes overlapped with 655 differentially regulated genes mentioned above, including 43 up-regulated and thirty-four down-regulated genes. We next investigated whether these genes expression correlated with Gd-IgA1 levels in IgAN patients. Pearson correlation analyses showed PTEN (phosphatase and tensin homolog) was the most powerful gene negatively correlated with Gd-IgA1 levels. CONCLUSIONS: These results demonstrated that dyregulated genes in patients with IgAN were enriched in intestinal immune network for IgA production and autophagy process, and PTEN in B cells might be involved in the mechanism of Gd-IgA1 production.

Galactose-deficient IgA1 in skin and serum from patients with skin-limited and systemic IgA vasculitis.

BACKGROUND: IgA vasculitis (IgAV) encompasses a systemic form involving kidneys, gut, skin, or joints, and a skin-limited form. One characteristic feature of systemic IgAV is deposition of galactose-deficient IgA1 (GD-IgA1) in kidneys (as in IgA nephropathy). The relevance of GD-IgA1 for cutaneous vasculitis is unknown. OBJECTIVE: We investigated whether GD-IgA1 is deposited perivascularly in systemic and also skin-limited IgAV and whether its serum levels differ between both forms. METHODS: In a case-control study, deposition of GD-IgA1 was analyzed immunohistochemically by KM55 antibody in skin biopsy specimens from 12 patients with skin-limited IgAV and 4 with systemic IgAV. GD-IgA1 levels were compared by enzyme-linked immunosorbent assay in sera from 15 patients each with skin-limited and systemic IgAV and from 11 healthy individuals. RESULTS: All biopsy samples from systemic IgAV, and also from skin-limited IgAV, revealed perivascular GD-IgA1 deposition. The average GD-IgA1 concentration in serum was significantly higher in systemic IgAV than in skin-limited IgAV, despite overlap between the groups. LIMITATIONS: Although high GD-IgA1 levels may be predictive of systemic IgAV, patient numbers were too low to determine cutoff values for systemic versus skin-limited IgAV. CONCLUSION: Perivascular GD-IgA1 deposition is a prerequisite for systemic and skin-limited IgAV; however, high GD-IgA1 levels in some patients with systemic IgAV suggest a dose-dependent effect of GD-IgA1 in IgAV.