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.

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.

Overactivation of the complement system may be involved in intrarenal arteriolar lesions in IgA nephropathy.

Introduction: IgA nephropathy (IgAN) encompasses a wide range of clinical and histology features. Some patients present without hematuria, with or without hypertension, still rapidly progress in renal function. Renal pathology of this part of patients were predominant intrarenal arteriolar lesions, rarely presented glomerular proliferative lesions. We aim to investigate the clinical and pathological characteristics and prognosis of these IgAN patients and initially explore whether the abnormal activation of complement is involved in the intrarenal arteriolar lesions of IgAN. Methods: A total of 866 patients with renal biopsy-proven IgAN diagnosed at Beijing Anzhen Hospital were recruited. IgAN patients without intrarenal arteriolar lesions and proliferative lesions were excluded (n = 115), the rest were divided into arteriolar lesions group (n = 202) and proliferative lesions group (n = 549). Among them, 255 patients were regularly followed up for at least 1 year. Renal biopsy tissues of 104 IgAN patients were stained for complement components by immunohistochemistry and immunofluorescence. Results: Compared with proliferative lesions group, the arteriolar lesions group experienced high percentage of hypertension (p = 0.004), low percentage of gross hematuria (p = 0.001), microscopic hematuria (p < 0.001) and less initial proteinuria (p = 0.033). Renal survival between the two groups was not significantly different (p = 0.133). MBL, C4d, FH and FHR5, C3c, and MAC deposited on intrarenal arteriole in arteriolar lesions group. Compare with the proliferative lesion group, the arteriolar lesions group exhibited a higher intensity of C3c deposition on the intrarenal arterioles (p = 0.048). C3c and CD31 co-deposited on intrarenal arterioles area in patients with intrarenal arteriolar lesions. Conclusion: Renal survival of the IgAN patients in arteriolar lesions group was not better than those in proliferative lesions group. Abnormal activation of complement may be involved in the pathogenesis of arteriolar damage through the injury of endothelial cells in this clinical phenotype of IgAN.

Collectin11 and Complement Activation in IgA Nephropathy.

BACKGROUND AND OBJECTIVES: IgA nephropathy is the most common primary GN worldwide. Previous research demonstrated that collectin11, an initiator of the complement lectin pathway, was involved in both AKI and chronic tubulointerstitial fibrosis. Here, we investigated the potential role of collectin11 in the pathogenesis of IgA nephropathy. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS: The deposition of collectin11 and other complement proteins was detected in glomeruli of 60 participants with IgA nephropathy by immunofluorescence. In vitro, human mesangial cells were treated with IgA1-containing immune complexes derived from participants with IgA nephropathy. Then, the expression of collectin11 in mesangial cells was examined by quantitative RT-PCR and immunofluorescence. The codeposition of collectin11 with IgA1 or C3 on mesangial cells was detected by immunofluorescence and proximity ligation assays. RESULTS: In total, 37% of participants with IgA nephropathy (22 of 60) showed codeposition of collectin11 with IgA in the glomerular mesangium. Using an injury model of mesangial cells, we demonstrated that IgA1-immune complexes derived from participants with IgA nephropathy increased the secretion of collectin11 in mesangial cells with the subsequent deposition of collectin11 on the cell surface via the interaction with deposited IgA1-immune complexes. In vitro, we found that collectin11 bound to IgA1-immune complexes in a dose-dependent but calcium-independent manner. Furthermore, deposited collectin11 initiated the activation of complement and accelerated the deposition of C3 on mesangial cells. CONCLUSIONS: In situ-produced collectin11 by mesangial cells might play an essential role in kidney injury in a subset of patients with IgA nephropathy through the induction of complement activation.

Glomerular Complement Factor H-Related Protein 5 is Associated with Histologic Injury in Immunoglobulin A Nephropathy.

INTRODUCTION: Immunoglobulin A nephrology (IgAN), characterized by co-deposition of IgA and complement components, is an activation of complement system involved disease. Factor H-related protein 5 (FHR-5) antagonized the ability of factor H to negatively regulate C3 activation, which leads to overactivation of the alternative pathway. Here we explore the relationship of intensity of glomerular FHR-5 deposition and severity of IgAN. METHODS: Renal staining of FHR-5 was detected by immunofluorescence, and plasma FHR-5 was detected by enzyme-linked immunosorbent assay in 56 patients with IgAN. The relationship of intensity of glomerular FHR-5 and clinical and pathologic features of these patients were further analyzed. RESULTS: Glomerular staining for FHR-5 was observed in a predominantly mesangial pattern in 32 biopsy specimens (57.1%). FHR-5 co-deposited with IgA and C3c in glomerular mesangial and capillary area in patients with IgAN. Patients with IgAN with Oxford endocapillary hypercellularity (P = 0.007) and segmental glomerulosclerosis (P = 0.049) presented with greater intensity of FHR-5 deposition. There were more cases with 2+ and 3+ FHR-5 staining in cohorts of 2+ and 3-4+ mesangial C3 deposition (P = 0.034) and IgA deposition (P = 0.019). Interestingly, the glomerular FHR-5 depositions were more abundant in male versus female in patients with IgAN (P = 0.002). Besides, circulating FHR-5 levels were elevated in patients with IgAN compared with healthy control subjects. Plasma FHR-5 levels were significantly higher in patients with mesangial hypercellularity at diagnosis than those with nonmesangial hypercellularity. CONCLUSIONS: We found that glomerular intensity of FHR-5 deposition could indicate the severity of histologic lesions of IgAN.

Variation in complement factor H affects complement activation in immunoglobulin A vasculitis with nephritis.

BACKGROUND: Immunoglobulin A (IgA) vasculitis with nephritis (IgAVN) and IgA nephropathy (IgAN) are widely considered as related diseases. Considerable evidences support the notion of involvement of complement activation in both IgAVN and IgAN. Our previous studies identified a genetic variant in complement factor H (CFH), rs6677604, as an IgAN-susceptible variant by genome-wide association study, and further confirmed its linkage to CFHR3-1Δ and proved its influence on complement activation and thereby on IgAN susceptibility. AIM: To explore the role of rs6677604 in complement activation of IgAVN. METHODS: In this study, we enrolled 632 patients with IgAVN, 1178 patients with IgAN and 902 healthy controls. The genotype of rs6677604 was measured by TaqMan allele discrimination assays or was extracted from genome-wide association study data. RESULTS: The frequency of the rs6677604-A allele was significantly higher in IgAVN than in IgAN. However, no significant differences were observed between IgAVN and the controls. Higher complement factor H (FH) levels were observed in IgAVN than IgAN, and positive correlation between circulating FH and C3 levels was present in IgAVN. In both IgAVN and IgAN, rs6677604-A was associated with less intensity of glomerular C3 deposits. In agreement with the higher frequency of rs6677604-A in IgAVN, the glomerular C3 deposits of patients with IgAVN were less intense than those in IgAN. CONCLUSION: Our findings suggest that genetic variation in CFH (rs6677604) is involved in the phenotype of complement activation in both IgAVN and IgAN. Moreover, rs6677604 might contribute to the difference of complement activation intensity between IgAVN and IgAN.

Immunological features and functional analysis of anti-CFH autoantibodies in patients with atypical hemolytic uremic syndrome.

OBJECTIVE: Atypical hemolytic uremic syndrome (aHUS) is associated with defective complement regulation. Anti-complement factor H (CFH) antibodies were thought to participate in the pathogenesis of aHUS. The aim of this study was to address the functions and properties of CFH autoantibodies in a Chinese Han cohort of aHUS patients. METHODS: Thirty-six anti-CFH antibody-positive aHUS patients at the acute phase of the disease were involved in this study. Clinical data of the patients were collected. Anti-CFH immunoglobulin G (IgG) subclasses and antibody isotypes were detected by ELISA. Epitope mapping was performed using recombinant CFH fragments (SCRs 1-4, SCR 7, SCRs 11-14, and SCRs 19-20). Purified IgG from plasma from seven patients were used for functional analyses. RESULTS: All patients presented with the classic triad of HUS. The anti-CFH autoantibodies mostly bound to the SCRs 19-20 domains of CFH but not the SCRs 1-4 domains. CFI cofactor activity was not disturbed by the anti-CFH antibody in any of the seven patients. Purified IgG interfered with the binding of CFH to C3b and CFH-mediated sheep erythrocyte protection in all seven patients. IgG from 4/5 (80%) patients tested inhibited the binding of CFH to glomerular endothelial cells. CONCLUSIONS: Our study suggests that the properties of CFH antibodies from patients with aHUS, including the recognition of SCRs and IgG subclasses, can influence and impair the biological role of CFH and therefore contribute to aHUS susceptibility.

Coding and Noncoding Variants in CFH Act Synergistically for Complement Activation in Immunoglobulin A Nephropathy.

BACKGROUND: In immunoglobulin A nephropathy (IgAN), complement activation occurs in both the systemic circulation and in situ (glomerular). A recent IgAN-genome-wide association study (GWAS) identified 1q32 as an IgAN susceptible locus that contained the complement regulatory protein coding gene complement factor H (CFH). Here, we explored the combined genetic effects of coding and noncoding variants in CFH, rs6677604 and rs800292 on complement activation in IgAN. METHODS: In total, 1,194 IgAN patients and 900 healthy controls who were the same as the Beijing Discovery Cohort in our recent IgAN-GWAS were recruited. The genotyping information of rs800292 and rs6677604 were extracted from GWAS data, while the information regarding plasma C3 levels and mesangial C3 deposits were collected from medical records. RESULTS: We found both rs800292-GG and rs6677604-GG were risk genotypes for complement activation in IgAN patients, as represented by lower plasma C3 levels in IgAN patients with rs800292-GG and a higher intensity of glomerular C3 deposits in those with rs6677604-GG, respectively. Additionally, IgAN patients with 2 risk genotypes (rs800292-GG and rs6677604-GG) showed a higher degree of complement activation compared to those with no risk genotypes (rs800292-AA/AG and rs6677604-AA/AG), as represented by both lower plasma C3 levels and a higher intensity of glomerular C3 deposits. Moreover, when compared to rs800292 or rs6677604 alone, the combined genetic effects of rs800292 and rs6677604 showed a stronger association with IgAN susceptibility. CONCLUSIONS: Our findings suggested that both coding and noncoding variants in CFH acted synergistically to regulate the degree of complement activation and thereby contributed to IgAN susceptibility.

Circulating complement factor H-related protein 5 levels contribute to development and progression of IgA nephropathy.

IgA nephropathy (IgAN) is a disease associated with activation of the complement system. But the factors influencing complement activation in IgAN are not fully understood. Complement factor H (FH) is an essential negative regulator of complement C3 activation. Complement factor H-related protein (FHR)-5 shares high sequence similarity with factor H. However, unlike factor H, on binding to activated C3 it enables further activation to proceed. Previously, we reported the contribution of rare variants of the CFHR5 gene to IgAN susceptibility. Here we compared circulating levels of FHR-5 in 1126 patients with IgAN and regular follow-up with those of 153 unrelated healthy individuals to explore the relationship of FHR-5 levels with IgAN development and progression. Circulating FHR-5 levels were significantly elevated in patients with IgAN compared to healthy individuals (median 4.55 [interquartile range 3.58 to 5.85] µg/ml vs 3.19 [interquartile range 2.55 to 3.92] µg/ml). Higher circulating FHR-5 levels were associated with a lower estimated glomerular filtration rate, hypertension, and severe Oxford-T and Oxford-C scores. High FHR-5 levels were independently and significantly associated with a risk of developing either a 30% decline in the estimated glomerular filtration rate or end-stage renal disease (hazard ratio, per standard deviation increment of natural square root transformed FHR-5 of 1.226; 95% confidence interval: 1.106-1.359). Thus, the circulating FHR-5 level is an independent risk factor for IgAN progression.

Mannose-Binding Lectin Levels Could Predict Prognosis in IgA Nephropathy.

IgA nephropathy (IgAN) is characterized by infections followed by episodic gross hematuria. Deficiency of mannose-binding lectin (MBL) is associated with recurrent infection in many diseases, but controversy exists regarding the role of MBL in IgAN. Here, we measured MBL2 variants and MBL levels in 749 patients with IgAN and 489 healthy controls. Overall, 5.2% (39 of 749) of patients with IgAN had MBL deficiency (MBL levels <100 ng/ml), among whom LYPB/LYPB and LXPA/LYPB were the predominant MBL2 haplotypes (82%; 32 of 39). We found a nonlinear association between MBL levels and renal outcome in IgAN. Patients with IgAN and MBL deficiency had a higher incidence of prodromic infections and gross hematuria than those with sufficient MBL levels (100-3540 ng/ml). Moreover, MBL deficiency independently associated with poor renal outcome in IgAN after multiple adjustments (hazard ratio, 5.18; 95% confidence interval, 2.50 to 10.72; P<0.001). Patients with high MBL levels (>3540 ng/ml) had more severe proteinuria and a higher proportion of crescents, although the association with IgAN progression did not reach statistical significance after adjustments. In conclusion, MBL deficiency and MBL excess may both have deleterious effects on IgAN progression, which suggests that MBL contributes to IgAN pathogenesis through multiple mechanisms.

Different types of glomerulonephritis associated with the dysregulation of the complement alternative pathway in 2 brothers: A case report.

RATIONALE: C3 glomerulonephritis (C3GN) and complement-mediated hemolytic uremic syndrome (HUS) both result from the abnormal regulation of the complement system. A significant number of patients with C3GN or complement-mediated HUS have mutations of more than 1 complement protein. This discovery has had a major impact on identifying the underlying cause of familial C3GN or complement-mediated HUS. PATIENT CONCERNS: We report the cases of 2 brothers (herein referred to as patient II-1 and patient II-9), both with complement disorders that differed in their clinical and genetic features. DIAGNOSES: Patient II-1 clinically presented with nephrotic syndrome and acute kidney injury and pathologically presented with C3GN combined with thrombotic microangiopathy (TMA) and subacute tubulointerstitial nephritis. Meanwhile, patient II-9 clinically presented with HUS and pathologically presented with TMA combined with acute severe tubular injury. INTERVENTIONS: Screenings for genetic mutations contributed to complement system dysregulation were performed on patient II-1. OUTCOMES: The genome sequencing identified that patient II-1 had a heterozygous mutation in the C3 gene (c.C1774T/p.R592W). Nine other relatives of the brothers were checked for this C3 mutation and only the daughter of patient II-1 (herein referred to as patient III-2) carried it, but so far, she does not have any clinical manifestations of kidney disease. LESSIONS: Family members with a dysregulation of the complement alternative pathway may differ in its clinical and genetic features.

Complement Alternative Pathway׳s Activation in Patients With Lupus Nephritis.

OBJECTIVE: The aim of this study was to detect the spectrum of complement activation pathways in circulation and to assess their correlations with clinical and pathologic features in a large lupus nephritis cohort from China. MATERIALS AND METHODS: Plasma levels of C1q, mannose-binding lectin, C4d, Bb, C3, C3a, C5a and soluble C5b-9 were detected by enzyme-linked immunosorbent assay in 222 patients with active biopsy-proven lupus nephritis, 34 patients with lupus nephritis at remission, 82 patients with active systemic lupus erythematosus without renal involvement and 39 normal controls. The correlations between levels of complement components and clinicopathological features of these patients were further analyzed. RESULTS: Plasma levels of C1q and C3 significantly decreased, and the levels of Bb, C3a, C5a and soluble C5b-9 were significantly elevated in patients with active lupus nephritis compared with those in remission, active systemic lupus erythematosus without renal involvement group and normal controls. In the lupus nephritis group, soluble C5b-9 levels were inversely correlated with C1q and C4d levels (r = -0.412, P < 0.001 and r = -0.221, P = 0.002, respectively), but more strongly correlated with the level of Bb (r = 0.546, P < 0.001). C3b, Bb and C5b-9 could colocalize on glomeruli in lupus nephritis. Plasma Bb level was significantly correlated with some renal disease activity indices and was a risk factor for renal outcomes (hazard ratio = 1.745; 95% CI: 1.106-2.754; P = 0.017) in the lupus nephritis group. CONCLUSIONS: Our findings suggested that the activation of the complement alternative pathway might play a more important role in the pathogenesis of lupus nephritis, and factor Bb might be a useful marker for evaluating renal disease activity and outcomes.

The clinical and laboratory features of Chinese Han anti-factor H autoantibody-associated hemolytic uremic syndrome.

BACKGROUND: Anti-complement factor H (CFH) autoantibody-associated hemolytic uremic syndrome (HUS) is a severe sub-type of HUS. METHODS: We assessed the clinical and renal pathological features, circulating complement levels, and genetic background of Chinese pediatric patients with this sub-type of HUS. Thirty-three consecutive patients with acute kidney injury who tested positive for serum anti-CFH autoantibodies were enrolled in this study. RESULTS: All of the eight patients who underwent renal biopsies presented with changes typical of thrombotic microangiopathy, especially changes in chronic characteristics. Compared to patients in remission and normal control subjects, patients with acute disease had significantly lower plasma CFH levels and significantly higher plasma complement 3a (C3a), C5a, and terminal complement complex (SC5b-9) levels. The CFH-anti-CFH immunoglobin G (IgG) circulating immunocomplex (CFH-CIC) titers were more closely correlated with CFH plasma levels than anti-CFH IgG levels. Of the 22 patients, four (18%) were homozygous for CFHR3-1Δ and ten were heterozygous for CFHR1 or CFHR3 deletions. Most patients responded well to a combination of plasma and immunosuppressive therapies, with a remission rate of 87%. At the end of the follow-up, nine patients reached the combined end-points, including two with end-stage renal disease and seven with relapses. CONCLUSION: Plasma C3a, C5a, and SC5b-9 levels predicted disease activity in anti-CFH autoantibody-associated HUS patients enrolled in this study. These patients responded well to plasma therapy combined with immunosuppression.