O-glycosylation of IgA1 and the pathogenesis of an autoimmune disease IgA nephropathy.

IgA nephropathy is a kidney disease characterized by deposition of immune complexes containing abnormally O-glycosylated IgA1 in the glomeruli. Specifically, some O-glycans are missing galactose that is normally ß1,3-linked to N-acetylgalactosamine of the core 1 glycans. These galactose-deficient IgA1 glycoforms are produced by IgA1-secreting cells due to a dysregulated expression and activity of several glycosyltransferases. Galactose-deficient IgA1 in the circulation of patients with IgA nephropathy is bound by IgG autoantibodies and the resultant immune complexes can contain additional proteins, such as complement C3. These complexes, if not removed from the circulation, can enter the glomerular mesangium, activate the resident mesangial cells, and induce glomerular injury. In this review, we briefly summarize clinical and pathological features of IgA nephropathy, review normal and aberrant IgA1 O-glycosylation pathways, and discuss the origins and potential significance of natural anti-glycan antibodies, namely those recognizing N-acetylgalactosamine. We also discuss the features of autoantibodies specific for galactose-deficient IgA1 and the characteristics of pathogenic immune complexes containing IgA1 and IgG. In IgA nephropathy, kidneys are injured by IgA1-containing immune complexes as innocent bystanders. Most patients with IgA nephropathy progress to kidney failure and require dialysis or transplantation. Moreover, most patients after transplantation experience a recurrent disease. Thus, a better understanding of the pathogenetic mechanisms is needed to develop new disease-specific treatments.

Effect of Telitacicept on Circulating Gd-IgA1 and IgA-Containing Immune Complexes in IgA Nephropathy.

Introduction: Telitacicept, a transmembrane activator and cyclophilin ligand interactor (TACI) fusion protein targeting B cell activating factor and a proliferation-inducing ligand (APRIL), has proven efficacy in treating Immunoglobulin A (IgA) nephropathy (IgAN). However, serum biomarkers that could predict the clinical response during the treatment remain unclear. Methods: Plasma samples from 24 participants in the phase 2 clinical trial were collected at baseline and after 4, 12, and 24 weeks; with 8 participants in the placebo group, 9 in the 160 mg group, and 7 in the 240 mg group. We measured the levels of galactose-deficient-IgA1 (Gd-IgA1), IgA-containing immune complexes, C3a, C5a, and sC5b-9. The association between the changes in these markers and proteinuria reduction was analyzed. Results: After 24 weeks of treatment, Gd-IgA1 decreased by 43.9% (95% confidence interval: 29.8%, 55.1%), IgG-IgA immune complex by 31.7% (14.4%, 45.5%), and poly-IgA immune complex by 41.3% (6.5%, 63.1%) in the 160 mg group; Gd-IgA1 decreased by 50.4% (38.6%, 59.9%), IgG-IgA immune complex decreased by 42.7% (29.5%, 53.4%), and poly-IgA immune complex decreased by 67.2% (48.5%,79.1%) in the 240 mg group. There were no significant changes in the circulatory C3a, C5a, or sC5b-9 levels during telitacicept treatment. Decreases in both plasma Gd-IgA1 and IgG-IgA or poly-IgA immune complexes were associated with proteinuria reduction. In turn, IgG-IgA or poly-IgA immune complexes showed a dose-dependent effect, consistent with proteinuria reduction during telitacicept treatment. Conclusion: Telitacicept lowered both circulating Gd-IgA1 and IgA-containing immune complexes, whereas IgA immune complex levels were more consistent with decreased proteinuria.

Complement system is overactivated in patients with IgA nephropathy after COVID-19.

IgA nephropathy (IgAN), which has been confirmed as a complement mediated autoimmune disease, is also one form of glomerulonephritis associated with COVID-19. Here, we aim to investigate the clinical and immunological characteristics of patients with IgAN after COVID-19. The level of plasma level of C5a (p < 0.001), soluble C5b-9 (p = 0.018), FHR5 (p < 0.001) were all significantly higher in Group CoV (33 patients with renal biopsy-proven IgAN experienced COVID-19) compared with Group non-CoV (44 patients with IgAN without COVID-19), respectively. Compared with Group non-CoV, the intensity of glomerular C4d (p = 0.017) and MAC deposition (p < 0.001) and Gd-IgA1 deposition (p = 0.005) were much stronger in Group CoV. Our finding revealed that for IgAN after COVID-19, mucosal immune responses to SARS-CoV-2 infection may result in the overactivation of systemic and renal local complement system, and increased glomerular deposition of Gd-IgA1, which may lead to renal dysfunction and promote renal progression in IgAN patients.

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.

The transcription factor HMGB2 indirectly regulates APRIL expression and Gd-IgA1 production in patients with IgA nephropathy.

BACKGROUND: IgA nephropathy (IgAN) is the most common primary glomerulonephritis worldwide. Proliferation-inducing ligand (APRIL) was identified as an important cause of glycosylation deficiency of IgA1 (Gd-IgA1), which can 'trigger' IgAN. Our previous study indicated that high migration group protein B2 (HMGB2) in peripheral blood mononuclear cells from patients with IgAN was associated with disease severity, but the underlying mechanism remains unclear. MATERIALS AND METHODS: The location of HMGB2 was identified by immunofluorescence. qRT-PCR and Western blotting were used to measure HMGB2, HMGA1, and APRIL expression. Gd-IgA1 levels were detected by enzyme-linked immunosorbent assay (ELISA). In addition, we used DNA pull-down, protein profiling, and transcription factor prediction software to identify proteins bound to the promoter region of the APRIL gene. RNA interference and coimmunoprecipitation (Co-IP) were used to verify the relationships among HMGB2, high mobility group AT-hook protein 1 (HMGA1), and APRIL. RESULTS: HMGB2 expression was greater in IgAN patients than in HCs and was positively associated with APRIL expression in B cells. DNA pull-down and protein profiling revealed that HMGB2 and HMGA1 bound to the promoter region of the APRIL gene. The expression levels of HMGA1, APRIL, and Gd-IgA1 were downregulated after HMGB2 knockdown. Co-IP indicated that HMGB2 binds to HMGA1. The Gd-IgA1 concentration in the supernatant was reduced after HMGA1 knockdown. HMGA1 binding sites were predicted in the promoter region of the APRIL gene. CONCLUSION: HMGB2 expression is greater in IgAN patients than in healthy controls; it promotes APRIL expression by interacting with HMGA1, thereby inducing Gd-IgA1 overexpression and leading to IgAN.

Nasal allergen-neutralizing antibodies correlate closely with tolerated intranasal allergen challenge dose following grass pollen subcutaneous immunotherapy in patients with local allergic rhinitis.

BACKGROUND: Local allergic rhinitis (LAR) is defined by chronic nasal symptoms, absence of atopy, positive nasal allergen challenge (NAC) and a good response to subcutaneous allergen immunotherapy (SCIT). We sought to investigate SCIT capacity to induce local and systemic blocking antibodies in LAR patients. METHODS: A RDBPC study of grass SCIT was performed, with participants receiving either SCIT (Group A; n = 10) or placebo (Group B; n = 14) in the first 6 months. Both groups subsequently received SCIT for 12 months at Year 2. Nasal and serum antibodies (IgG4, IgA1 and IgA2) and their inhibitory capacity were measured at multiple timepoints. RESULTS: The allergen concentration tolerated increased significantly at 6 months (Group A; p = .047) and 24 months (Group B; p = .049) compared with baseline and persisted until the end of the study. Induction of serum sIgA1 to Phl p was seen in Groups A and B, albeit the former being induced earlier (1.71-fold, p = .027). A significant induction in sIgG4 to Phl p 1 and 5 was observed in serum of Group A (p = .047 and p = .0039) and sIgA2 to Phl p in Group B (p = .032 and p = .0098) at 18 and 24 months, respectively. Both local and systemic blocking antibodies can inhibit allergen-IgE complexes binding to CD23 on B cells, and this correlated with level of allergen tolerated intra-nasally in Group A (serum; 𝜌 = -.47, p = .0006, nasal; 𝜌 = -.38, p = .0294). CONCLUSIONS: Grass pollen SCIT induced functional systemic blocking antibodies that correlate with the concentration of allergen tolerated following NAC, highlighting their potential as a biomarker of SCIT in LAR.

Examining the association between serum galactose-deficient IgA1 and primary IgA nephropathy: a systematic review and meta-analysis.

BACKGROUND: IgA nephropathy (IgAN) is a common primary glomerular disease. The O-glycosylation status of IgA1 plays a crucial role in disease pathophysiology. The level of poorly-O-galactosylated IgA1, or galactose-deficient IgA1 (Gd-IgA1), has also been identified as a potential biomarker in IgAN. We sought to examine the value of serum Gd-IgA1 as a biomarker in IgAN, by investigating its association with clinical, laboratory, and histopathological features of IgAN. METHODS: The review followed Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) recommendations and was registered in PROSPERO (CRD42021287423). The literature search was conducted in PubMed, Web of Science, Cochrane, and Scopus, and the selected articles were evaluated for eligibility based on predefined criteria. The methodological quality of the studies was assessed using the Newcastle-Ottawa Scale. Statistical analysis was performed to calculate effect sizes and assess heterogeneity among the studies. RESULTS: This review analyzed 29 out of 1,986 studies, conducted between 2005 and 2022, with participants from multiple countries. Gd-IgA1 levels were not associated with age and gender, while associations with hypertension, hematuria, and proteinuria were inconsistent. In the meta-analyses, a correlation between serum Gd-IgA1 and estimated glomerular filtration rate was identified, however, the relationships between Gd-IgA1 levels and chronic kidney disease (CKD) stage and progression to kidney failure were inconsistent. CONCLUSIONS: Serum Gd-IgA1 levels were not associated with validated prognostic risk factors, but were negatively correlated with kidney function. Further research in larger studies using standardized assays are needed to establish the value of Gd-IgA1 as a prognostic risk factor in IgAN.

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.

LIF/JAK2/STAT1 Signaling Enhances Production of Galactose-Deficient IgA1 by IgA1-Producing Cell Lines Derived From Tonsils of Patients With IgA Nephropathy.

Introduction: Galactose-deficient IgA1 (Gd-IgA1) plays a key role in the pathogenesis of IgA nephropathy (IgAN). Tonsillectomy has been beneficial to some patients with IgAN, possibly due to the removal of tonsillar cytokine-activated cells producing Gd-IgA1. To test this hypothesis, we used immortalized IgA1-producing cell lines derived from tonsils of patients with IgAN or obstructive sleep apnea (OSA) and assessed the effect of leukemia inhibitory factor (LIF) or oncostatin M (OSM) on Gd-IgA1 production. Methods: Gd-IgA1 production was measured by lectin enzyme-linked immunosorbent assay; JAK-STAT signaling in cultured cells was assessed by immunoblotting of cell lysates; and validated by using small interfering RNA (siRNA) knock-down and small-molecule inhibitors. Results: IgAN-derived cells produced more Gd-IgA1 than the cells from patients with OSA, and exhibited elevated Gd-IgA1 production in response to LIF, but not OSM. This effect was associated with dysregulated STAT1 phosphorylation, as confirmed by STAT1 siRNA knock-down. JAK2 inhibitor, AZD1480 exhibited a dose-dependent inhibition of the LIF-induced Gd-IgA1 overproduction. Unexpectedly, high concentrations of AZD1480, but only in the presence of LIF, reduced Gd-IgA1 production in the cells derived from patients with IgAN to that of the control cells from patients with OSA. Based on modeling LIF-LIFR-gp130-JAK2 receptor complex, we postulate that LIF binding to LIFR may sequester gp130 and/or JAK2 from other pathways; and when combined with JAK2 inhibition, enables full blockade of the aberrant O-glycosylation pathways in IgAN. Conclusion: In summary, IgAN cells exhibit LIF-mediated overproduction of Gd-IgA1 due to abnormal signaling. JAK2 inhibitors can counter these LIF-induced effects and block Gd-IgA1 synthesis in IgAN.

IgA nephropathy: gut microbiome regulates the production of hypoglycosilated IgA1via the TLR4 signaling pathway.

BACKGROUND: IgA nephropathy (IgAN) is a major cause of primary glomerulonephritis characterized by mesangial deposits of galactose-deficient IgA1 (Gd-IgA1). Toll-like receptors (TLRs), particularly TLR4 are involved in the pathogenesis of IgAN. The role of gut microbiota on IgAN patients was recently investigated. However, whether gut microbial modifications of Gd-IgA1 through TLR4 play a role in IgAN remains unclear. METHODS: We recruited subjects into four groups, including 48 patients with untreated IgAN, 22 treated IgAN patients (IgANIT), 22 primary membranous nephropathy (MN), and 31 healthy controls (HCs). Fecal samples were collected to analyze changes in gut microbiome. Gd-IgA1 levels, expression of TLR4, B-cell stimulators, and intestinal barrier function were evaluated in all subjects. C57BL/6 mice were treated with a broad-spectrum antibiotic cocktail to deplete the gut microbiota and then gavaged with fecal microbiota transplanted fromclinical subjects of every group. Gd-IgA1 and TLR4 pathway were detected in peripheral blood mononuclear cells (PBMCs) from IgAN and HCs co-incubated with Lipopolysaccharide (LPS) and TLR4 inhibitor. RESULTS: Compared with other three groups, different compositions and decreased diversity demonstrated gut dysbiosis in un-treated IgAN, especially the enrichment of Escherichia -Shigella. Elevated Gd-IgA1 levels were found in un-treated IgAN patients and correlated with gut dysbiosis, TLR4, B-cell stimulators, indexes of intestinal barrier damage, and proinflammatory cytokines. In vivo, mice colonized with gut microbiota from IgAN and IgANIT patients, copied the IgAN phenotype with the activation of TLR4/MyD88/NF-κB pathway, B-cell stimulators in the intestine, and complied with enhanced proinflammatory cytokines. In vitro, LPS activated TLR4/MyD88/NF-κB pathway, B-cell stimulators and proinflammatory cytokines in the PBMCs from IgAN patients, which resulted in overproduction of Gd-IgA1 and inhibited by TLR4 inhibitor. CONCLUSIONS: Our results illustrated that gut-kidney axis was involved in the pathogenesis of IgAN. Gut dysbiosis could stimulate the overproduction of Gd-IgA1 by TLR4 signaling pathway production and B-cell stimulators.

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.

Into the Dark Serum Proteome: Personalized Features of IgG1 and IgA1 Repertoires in Severe COVID-19 Patients.

Serum proteomics has matured and is now able to monitor hundreds of proteins quantitatively in large cohorts of patients. However, the fine characteristics of some of the most dominant proteins in serum, the immunoglobulins, are in these studies often ignored, due to their vast, and highly personalized, diversity in sequences. Here, we focus exclusively on these personalized features in the serum proteome and distinctively chose to study individual samples from a low diversity population: elderly donors infected by severe acute respiratory syndrome corona virus 2 (SARS-CoV-2). By using mass spectrometry-based methods, immunoglobulin IgG1 and IgA1 clonal repertoires were monitored quantitatively and longitudinally in more than 50 individual serum samples obtained from 17 Corona virus disease 2019 patients admitted to intensive care units. These clonal profiles were used to examine how each patient reacted to a severe SARS-CoV-2 infection. All 17 donors revealed unique polyclonal repertoires and substantial changes over time, with several new clones appearing following the infection, in a few cases leading to a few, very high, abundant clones dominating their repertoire. Several of these clones were de novo sequenced through combinations of top-down, middle-down, and bottom-up proteomics approaches. This revealed sequence features in line with sequences deposited in the SARS-CoV-specific antibody database. In other patients, the serological Ig profiles revealed the treatment with tocilizumab, that subsequently dominated their serological IgG1 repertoire. Tocilizumab clearance could be monitored, and a half-life of approximately 6 days was established. Overall, our longitudinal monitoring of IgG1 and IgA1 repertoires of individual donors reveals that antibody responses are highly personalized traits of each patient, affected by the disease and the chosen clinical treatment. The impact of these observations argues for a more personalized and longitudinal approach in patients' diagnostics, both in serum proteomics as well as in monitoring immune responses.

The contribution of a proliferation-inducing ligand (APRIL) and other TNF superfamily members in pathogenesis and progression of IgA nephropathy.

Advances in our understanding of the pathogenesis of immunoglobulin A nephropathy (IgAN) have led to the identification of novel therapeutic targets and potential disease-specific treatments. Specifically, a proliferation-inducing ligand (APRIL) has been implicated in the pathogenesis of IgAN, mediating B-cell dysregulation and overproduction of pathogenic galactose-deficient IgA1 (Gd-IgA1). Animal and clinical studies support the involvement of APRIL in the pathogenesis and progression of IgAN. An elevated level of APRIL is found in IgAN when compared with controls, which correlates with the level of Gd-IgA1 and associates with more severe disease presentation and worse outcomes. Conversely, anti-APRIL therapy reduces pathogenic Gd-IgA1 and IgA immune complex formation and ameliorates the severity of kidney inflammation and injury. Genome-wide association studies in IgAN have identified TNFSF13 and TNFRSF13B, a cytokine ligand-receptor gene pair encoding APRIL and its receptor, respectively, as risk susceptibility loci in IgAN, further supporting the causal role of the APRIL signalling pathway in IgAN. Several novel experimental agents targeting APRIL, including atacicept, telitacicept, zigakibart and sibeprenlimab, are currently under investigation as potential therapies in IgAN. Preliminary results suggest that these agents are well-tolerated, and reduce levels of Gd-IgA1, with corresponding improvement in proteinuria. Further studies are ongoing to confirm the safety and efficacy of anti-APRIL approaches as an effective therapeutic strategy in IgAN.

Diagnostic and prognostic value of galactose-deficient IgA1 in patients with IgA nephropathy: an updated systematic review with meta-analysis.

Objectives: Galactose-deficient IgA1 (Gd-IgA1) is a critical effector molecule in the pathogenesis of IgA nephropathy (IgAN), a leading renal disease without noninvasive assessment options. This updated systematic review aimed to determine the diagnostic and prognostic value of Gd-IgA1 assessment in biological fluids in patients with IgAN. Methods: PRISMA guidelines were followed in this review. We searched PubMed, Embase, Cochrane Library, China National Knowledge Infrastructure, China Biology Medicine disc, VIP Information/China Science and Technology Journal Database, and WANFANG for studies published between database inception and January 31, 2023. Eligible studies that evaluated aberrant IgA1 glycosylation in IgAN patients relative to controls were identified, and random effects meta-analyses were used to compare Gd-IgA1 levels in different groups. The quality of the evidence was assessed using the Newcastle-Ottawa Scale. This study was registered on PROSPERO (CRD42022375246). Findings: Of the 2727 records identified, 50 were eligible and had available data. The mean Newcastle-Ottawa Scale score was 7.1 (range, 6-8). Data synthesis suggested that IgAN patients had higher levels of blood and/or urine Gd-IgA1 compared with healthy controls (standard mean difference [SMD]=1.43, 95% confidence interval [CI]=1.19-1.68, P<0.00001), IgA vasculitis patients (SMD=0.58, 95% CI=0.22-0.94, P=0.002), and other kidney disease patients (SMD=1.06, 95% CI=0.79-1.33, P<0.00001). Moreover, patients with IgAN had similar levels of serum Gd-IgA1 compared to first-degree relatives (SMD=0.38, 95% CI= -0.04-0.81, P=0.08) and IgA vasculitis with nephritis patients (SMD=0.12, 95% CI= -0.04-0.29, P=0.14). In addition, ten studies demonstrated significant differences in serum Gd-IgA1 levels in patients with mild and severe IgAN (SMD= -0.37, 95% CI= -0.64--0.09, P=0.009). Conclusions: High serum and urine Gd-IgA1 levels suggest a diagnosis of IgAN and a poor prognosis for patients with this immunological disorder. Future studies should use more reliable and reproducible methods to determine Gd-IgA1 levels. Systematic review registration: https://www.crd.york.ac.uk/prospero/display_record.php?ID=CRD42022375246, identifier CRD42022375246.

Characterization of patients with IgA nephropathy with and without associated minimal change disease.

Introduction: Immunoglobulin A nephropathy (IgAN) presents various clinical manifestations and pathological phenotypes. Approximately 5% of patients with IgAN present with early onset nephrotic syndrome, mild mesangial lesions, and diffuse foot process effacement of podocytes, which resemble minimal change disease (MCD). These patients are defined as MCD-IgAN. Whether MCD-IgAN is a special type of IgAN or simply MCD accompanied by IgA deposition remains controversial. Methods: A total of 51 patients diagnosed with MCD-IgAN at Beijing Anzhen Hospital from January 2010 to September 2022 were recruited. The clinical and pathological characteristics of IgA-MCD were analyzed. Patients with IgAN but without MCD (non-MCD-IgAN) and healthy participants were enrolled as controls. Galactose-deficient immunoglobulin A1 (Gd-IgA1) and complement C3 were detected both in the circulation and in renal tissues. Results: We found that the levels of serum Gd-IgA1 were lower in participants with MCD-IgAN than in those with non-MCD-IgAN, but higher than in healthy participants. Gd-IgA1 was rarely deposited in the glomeruli of participants with MCD-IgAN, with a positive rate of only 13.7% (7/51); in contrast, the positive rate in participants with non-MCD-IgAN was 82.4% (42/51). Among renal Gd-IgA1-positive patients, Gd-IgA1 and immunoglobulin A (IgA) colocalized along the glomerular mesangial and capillary areas. Interestingly, we found that the circulating levels of complement C3 were significantly higher in participants with MCD-IgAN than in participants with non-MCD-IgAN. In addition, the intensity of C3c in glomeruli in participants with MCD-IgAN was significantly weaker than in participants with non-MCD-IgAN. Conclusions: Our study suggests that, in MCD-IgAN, most of the IgA that is deposited on glomeruli is not the same pathogenic Gd-IgA1 as found in general IgAN. Complement activation both in the circulation and in the renal locality was much weaker in MCD-IgAN than in non-MCD-IgAN. Our study suggests that IgAN with MCD might be MCD with coincidental IgA deposition.

Immunoglobulin A Glycosylation Differs between Crohn's Disease and Ulcerative Colitis.

Inflammatory bowel diseases (IBD), such as Crohn's disease (CD) and ulcerative colitis (UC), are chronic and relapsing inflammations of the digestive tract with increasing prevalence, yet they have unknown origins or cure. CD and UC have similar symptoms but respond differently to surgery and medication. Current diagnostic tools often involve invasive procedures, while laboratory markers for patient stratification are lacking. Large glycomic studies of immunoglobulin G and total plasma glycosylation have shown biomarker potential in IBD and could help determine disease mechanisms and therapeutic treatment choice. Hitherto, the glycosylation signatures of plasma immunoglobulin A, an important immunoglobulin secreted into the intestinal mucin, have remained undetermined in the context of IBD. Our study investigated the associations of immunoglobulin A1 and A2 glycosylation with IBD in 442 IBD cases (188 CD and 254 UC) and 120 healthy controls by reversed-phase liquid chromatography electrospray-ionization mass spectrometry of tryptic glycopeptides. Differences of IgA O- and N-glycosylation (including galactosylation, bisection, sialylation, and antennarity) between patient groups were associated with the diseases, and these findings led to the construction of a statistical model to predict the disease group of the patients without the need of invasive procedures. This study expands the current knowledge about CD and UC and could help in the development of noninvasive biomarkers and better patient care.

[Effect of pasteurization and freezing on the content of IgA1 and IgA2 subtypes in breast milk]. / Reducción del contenido de IgA1 e IgA2 en la leche materna por efecto de la pasteurización y congelación.

OBJECTIVE: To determine the effect of pasteurization and freezing on the content of IgA1 and IgA2 in breast milk. METHODS: Observational, retrospective study, carried out in women who had been breastfeeding their newborn for more than 30 days, and could donate 50 mL of milk. The concentration of IgA1 and IgA2 was determined by turbidimetry, before and after being subjected to pasteurization and freezing, every 15 days for 2 months. Freezing was at -20°C. A total IgA content of 1598.5 mg/dL was found. RESULTS: 10 breast milk donors were selected. The initial concentration of IgA1 and IA2 was 651 and 945.7 mg/dL, respectively; At the end of the freezing times, the content of both immunoglobulins decreased: IgA1 of 74% and IgA2 of 86%. After the treatments, the immunoglobulin content decreased dramatically, with a significant difference of p < 0.05. CONCLUSIONS: Pasteurization and freezing significantly affect the content of IgA1 and IgA in breast milk; therefore, breast-feeding remains the best way to offer full immunological protection to the infant.

OBJECTIVO: Determinar el efecto de la pasteurización y congelación en el contenido de IgA1 e IgA2 en la leche materna. MÉTODOS: Estudio observacional y retrospectivo, llevado a cabo en mujeres que tuvieran más de 30 días de ofrecer lactancia a su neonato, y pudieran donar 50 mL de leche. Se determinó la concentración de IgA1 e IgA2 mediante turbidimetría, antes y después de someterse a pasteurización y congelación, cada 15 días durante 2 meses. La congelación fue a ­20°C. Se encontró un contenido total de IgA de 1598,5 mg/dL. RESULTADOS: Se seleccionaron 10 donantes de leche materna. La concentración inicial de IgA1 e IA2 fue de 651 y 945.7 mg/dL, respectivamente; al finalizar los tiempos de congelación disminuyó el contenido de ambas inmunoglobulinas: IgA1 del 74% e IgA2 del 86%. Después de los tratamientos, el contenido de inmunoglobulinas disminuyó de forma contundente, con diferencia significativa de p < 0.05. CONCLUSIONES: La pasteurización y la congelación afectan de manera importante el contenido de IgA1 e IgA en la leche materna; por tanto, la alimentación al seno materno sigue siendo la mejor forma de ofrecer toda protección inmunológica al lactante.

Follicular Helper T Cells In Peyer's Patches And Galactose-Deficient Iga1 Contribute To Iga Nephropathy.

BACKGROUND: Common primary glomerulonephritis with aberrant mucosal immunity is IgA nephropathy (IgAN). T follicular helper (TFH) cells are essential in regulating B cell differentiation. Peyer's patches (PPs) are the main site where IgA+ plasmablasts differentiate. OBJECTIVE: Our study aimed to investigate the TFH cell's potential contribution to the etiology of IgA nephropathy. MATERIALS AND METHODS: In PPs from IgAN mouse models, the ratio of the TFH cell, B220+IgA+, B220+IgM+, and B220-IgA+ lymphocytes were assessed. Then, we used Western blot to assess the expression of Bcl-6, Blimp- 1, and IL-21 proteins in PPs and used RT-PCR to assess the expression of IL-21 and TGF- 1 mRNA. TFH cells coculture with spleen cells to measure the degree of IL-21 and the ratio of activation marker CD69 on the TFH cells. Naive B cells (CD27-IgD+) from children suffering from IgAN were cultured with TFH cell-related cytokines. The supernatant was detected to assess the excretion of galactose-deficient IgA1 (Gd-IgA1). RESULTS: IgAN mice developed noticeably increased degrees of IL-21 and CD69 on TFH cells than controls did, as well as higher percentages of B220+IgA+, B220+IgM+, B220+IgA+, TGF- 1, and IL-21 mRNA and Bcl-6, IL-21 proteins in PPs. The Gd-IgA1 level in the supernatant and IgAN- positive children's serum were noticeably higher than those of the healthy controls (P < 0.05). PPs provide the microenvironment to induce the production of IgA-secreting plasmablasts. CONCLUSION: TFH cells may be a key moderator to induce B cell differentiation into IgA-secreting plasmablasts and produce Gd-IgA1, which plays a significant part in IgAN's pathogenesis. It could be a new therapeutic target in the future.

Immune abnormalities in IgA nephropathy.

Immunoglobulin A (IgA) nephropathy (IgAN) is the most common primary glomerulonephritis worldwide and it is characterized by mesangial IgA deposition. Asymptomatic hematuria with various degrees of proteinuria is the most common clinical presentation and up to 20%-40% of patients develop end-stage kidney disease within 20 years after disease onset. The pathogenesis of IgAN involves four sequential processes known as the "four-hit hypothesis" which starts with the production of a galactose-deficient IgA1 (gd-IgA1), followed by the formation of anti-gd-IgA1 IgG or IgA1 autoantibodies and immune complexes that ultimately deposit in the glomerular mesangium, leading to inflammation and injury. Although several key questions about the production of gd-IgA1 and the formation of anti-gd-IgA1 antibodies remain unanswered, a growing body of evidence is shedding light on the innate and adaptive immune mechanisms involved in this complex pathogenic process. Herein, we will focus on these mechanisms that, along with genetic and environmental factors, are thought to play a key role in disease pathogenesis.

Corrigendum: Concurrent IgA nephropathy and membranous nephropathy, is it an overlap syndrome?

[This corrects the article DOI: 10.3389/fimmu.2022.846323.].