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Uncontrolled activation of the alternative pathway (AP) of complement, due to genetic and/or acquired defects, plays a primary pathogenetic role in C3 glomerulopathy (C3G), a rare and heterogeneous disease characterised by predominant C3 fragment deposition within the glomerulus, as well as glomerular damage. There are currently no approved disease-specific treatments for C3G, but new drugs that directly counteract AP dysregulation, targeting components of the pathway, have opened promising new perspectives for managing the disease. Complement factor B (FB), which is primarily synthesised by hepatocytes, is a key component of the AP, as it drives the central amplification loop of the complement system. In this study we used a GalNAc (N-Acetylgalactosamine)-conjugated siRNA to selectively target and suppress liver FB expression in two mouse models characterised by the complete (Cfh -/- mice) or partial (Cfh +/- ) loss of function of complement factor H (FH). Homozygous deletion of FH induced a severe C3G phenotype, with strong dysregulation of the AP of complement, glomerular C3 deposition and almost complete C3 consumption. Mice with a heterozygous deletion of FH had intermediate C3 levels and exhibited slower disease progression, resembling human C3G more closely. Here we showed that FB siRNA treatment did not improve serum C3 levels, nor limit glomerular C3 deposition in Cfh -/- mice, while it did normalise circulating C3 levels, reduce glomerular C3 deposits, and limit mesangial electron-dense deposits in Cfh +/- mice. The present data provide important insights into the potential benefits and limitations of FB-targeted inhibition strategies and suggest RNA interference-mediated FB silencing in the liver as a possible therapeutic approach for treating C3G patients with FH haploinsufficiency. • A GalNAc FB siRNA silences liver FB gene expression in Cfh -/- and Cfh +/- mice. • FB siRNA reduces circulating FB levels in both the Cfh -/- and Cfh +/- mice. • Serum C3 levels are normalized by treatment with FB siRNA only in Cfh +/- mice. • FB siRNA reduces glomerular C3 and mesangial electron-dense deposits in Cfh +/- mice. [ABSTRACT FROM AUTHOR]

Sensorineural hearing loss is associated with dysfunction of cochlear cells. Although immune cells play a critical role in maintaining the inner ear microenvironment, the precise immune-related molecular mechanisms underlying the pathophysiology of hearing loss remain unclear. The complement cascade contributes to the regulation of immune cell activity. Additionally, activation of the complement cascade can lead to the cellular opsonization of cells and pathogens, resulting in their engulfment and elimination by phagocytes. Complement factor B (fB) is an essential activator protein in the alternative complement pathway, and variations in the fB gene are associated with age-related macular degeneration. Here we show that mice of both sexes deficient in fB functional alleles (fB-/-) demonstrate progressive hearing impairment. Transcriptomic analysis of auditory nerves from adult mice detected 706 genes that were significantly differentially expressed between fB-/- and wild-type control animals, including genes related to the extracellular matrix and neural development processes. Additionally, a subset of differentially expressed genes was related to myelin function and neural crest development. Histological and immunohistochemical investigations revealed pathological alterations in auditory nerve myelin sheathes of fB-/- mice. Pathological alterations were also seen in the stria vascularis of the cochlear lateral wall in these mice. Our results implicate fB as an integral regulator of myelin maintenance and stria vascularis integrity, underscoring the importance of understanding the involvement of immune signaling pathways in sensorineural hearing loss. [ABSTRACT FROM AUTHOR]

Sensorineural hearing loss is associated with dysfunction of cochlear cells. Although immune cells play a critical role in maintaining the inner ear microenvironment, the precise immune-related molecular mechanisms underlying the pathophysiology of hearing loss remain unclear. The complement cascade contributes to the regulation of immune cell activity. Additionally, activation of the complement cascade can lead to the cellular opsonization of cells and pathogens, resulting in their engulfment and elimination by phagocytes. Complement factor B (fB) is an essential activator protein in the alternative complement pathway, and variations in the fB gene are associated with age-related macular degeneration. Here we show that mice of both sexes deficient in fB functional alleles (fB−/−) demonstrate progressive hearing impairment. Transcriptomic analysis of auditory nerves from adult mice detected 706 genes that were significantly differentially expressed between fB−/− and wild-type control animals, including genes related to the extracellular matrix and neural development processes. Additionally, a subset of differentially expressed genes was related to myelin function and neural crest development. Histological and immunohistochemical investigations revealed pathological alterations in auditory nerve myelin sheathes of fB−/− mice. Pathological alterations were also seen in the stria vascularis of the cochlear lateral wall in these mice. Our results implicate fB as an integral regulator of myelin maintenance and stria vascularis integrity, underscoring the importance of understanding the involvement of immune signaling pathways in sensorineural hearing loss.

Immune checkpoint inhibitors (ICIs) have made an important contribution to the survival of patients with certain cancers. ICIs interrupt co-inhibitory signaling pathways mediated by programmed cell death protein 1 (PD-1), programmed cell death protein ligand 1 (PD-L1) and cytotoxic T lymphocyte-associated antigen (CTLA-4) that result in the elimination of cancer cells by stimulating the immune system. However, immune-related adverse events have also been described and attributed to an enhanced immune system activation. Recent observations have suggested a dysregulation of immune checkpoints in active antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV). We here analyzed intrarenal PD-1 and PD-L1 by immunostaining in a total of 15 kidney biopsies with ANCA-associated renal vasculitis in correlation with glomerular and tubulointerstitial lesions. For independent validation, publicly available datasets were analyzed for PD-1 expression (encoded by PDCD1). We here observed a predominant tubulointerstitial expression of PD-1 that is decreased in ANCA-associated renal vasculitis. Moreover, loss of tubulointerstitial PD-1 correlated with active ANCA-associated renal vasculitis. Consistent with the observed association with active glomerular and tubulointerstitial lesions, we identified that interstitial PD-1 correlated with tubular and/or glomerular PD-L1 positivity. Finally, PD-1 was associated with decreased local synthesis of complement factor B. Interestingly, we did not observe a correlation between PD-1 and complement C5 or its C5a receptor. Combined with our observations, this may implicate a link between impaired PD-1/PD-L1 signaling, complement factor B and active ANCA-associated renal vasculitis. These findings could be of relevance because experimental data have already described that PD-1 agonism can be used therapeutically to attenuate autoimmunity in multiple disease models. Furthermore, targeted therapy against a complement C5/C5a receptor and factor B are both available and currently evolving in the treatment of AAV. Therefore, this pilot study expands our current knowledge and describes a potential interplay between immune checkpoints and the alternative complement pathway in active ANCA-associated renal vasculitis. [ABSTRACT FROM AUTHOR]

Objectives: We aimed to define the relationships between the serum concentrations of complement factors B and H in mid-pregnancy and the risk of preeclampsia (PE) in patients with gestational diabetes mellitus (GDM).Study Design: We performed a prospective nested case-control study of 503 patients with GDM who attended Peking University Third Hospital between March 2018 and December 2018. 456 patients were followed until delivery and blood samples were collected between gestational weeks 24 and 28. Thirty patients developed PE, 12 developed gestational hypertension (GH), and 42 matched cases were selected as a control group.Results: The incidence of PE was 5.96 %. The serum concentrations of triacylglycerol (TG), FB, and FH of women with GDM who developed PE (GDM-PE group) in mid-pregnancy were significantly higher than those of the GDM group [TG: 3.60 (2.94-4.63) vs 2.54 (2.14-3.01) mmol/L, p < 0.001; FB: 346 (314-378) vs 284 (263-323) mg/L, p < 0.001; FH: 417 ± 45 vs 379 ± 47 mg/L, p = 0.003]. Multivariate regression analysis showed that high serum concentrations of TG and FB in mid-pregnancy were related to the risk of patients with GDM developing PE [TG: odds ratio (OR) 2.035 (95 % confidence interval (CI) 1.032-4.013); FB: OR 1.018 (95 % CI 1.001-1.035)]. The area under the curve (AUC) of FB for the prediction of PE was 0.821 (95 % CI 0.722-0.921) and that for a combination of TG, FB, and FH was 0.857 (95 % CI 0.770-0.944).Conclusions: High serum FB concentration during mid-pregnancy is a potential predictor of the risk of PE in patients with GDM, and the combination of FB, FH, and TG increased this predictive value. [ABSTRACT FROM AUTHOR]

Lung adenocarcinoma (LUAC) as the most common lung cancer, and its incidence is increasing. Complement factor B (CFB) is an important factor in the alternative complement pathway. CFB has been reported to be involved in the progression of many cancers, including in pancreatic cancer, cutaneous squamous cell carcinoma, and nasopharyngeal carcinoma, but the function and molecular mechanism of CFB in LUAC remains unclear. The present study aimed to explore the role of CFB in LUAC malignant progression. In our previous study, we found that CFB was downregulated expression in LUAC clinical samples. Here, we firstly detected the cell function in vitro. Cell proliferation and migration were increased, while cell apoptosis and cell cycle arrest were suppressed after CFB knockdown. Overexpression of CFB repressed the malignant progression of LUAC in vitro. Besides, in vivo experiments revealed that upregulation of CFB inhibited tumor growth and Ki67 expression. Additionally, our data indicated that CFB negatively regulated Ras/mitogen-activated protein kinase (MAPK) signaling pathway. Furthermore, upregulation of CFB inhibited the progression of LUAC was reversed by Ras/MAPK pathway activators (ML-098 or C16-PAF). Our study uncovered that CFB acts as a tumor suppressor repressed tumorigenesis of LUAC through inhibiting the Ras/MAPK pathway, suggesting that CFB may be a potential biomarker and therapeutic target for LUAC. [Display omitted] • CFB acts as an anti-cancer factor that inhibits cell proliferation and migration, promotes apoptosis and cell cycle arrest, thus inhibiting the malignant progression of LUAC. • CFB inhibits LUAC tumor growth in vivo. • CFB inhibits activation of the Ras/mediator-activated protein kinase (MAPK) signaling pathway. • Ras/MAPK pathway activators (ML-098 or C16-PAF) reverse the inhibitory effect of CFB upregulation on LUAC progression. [ABSTRACT FROM AUTHOR]

Purified FB or serial dilutions of serum is mixed with the depleted serum, allowing for APC-mediated hemolysis proportional to the amount of FB in the sample. C5b-9 deposition induced by sialidase treatment in patient serum and NHS correlates with cell killing in the mHam and indicates that APC function is impaired in patient serum. However, in the presence of patient serum, treatment of cells with sialidase did not lead to increased C5b-9 deposition above NHS (0.3% in untreated cells vs 1.85% in sialidase-treated cells). The lack of complement activation due to sialidase in patient serum but intact complement-mediated cell killing with STX-1 suggests the patient's mutation in FB disrupts APC function. [Extracted from the article]

Activation of the alternative pathway (AP) of complement is thought to play an important role in Immunoglobin A nephropathy (IgAN). Our previous study showed that rs4151657 within the complement factor B (CFB) gene increased the risk of IgAN. The protein encoded by the CFB gene is an initial factor that promotes AP activation. The aim of this study was to investigate whether other variants of CFB confer susceptibility to IgAN and elucidate their potential roles in AP activation. A total of 1,350 patients with IgAN and 1,420 healthy controls were enrolled and five tag single-nucleotide polymorphisms were selected for genotyping. The levels of key AP components, such as CFB, complement factor H and complement split product C3a, were measured by enzyme-linked immunosorbent assay. Molecular docking and molecular dynamic simulation were carried out to characterize the mutation of residues in the protein structure and the dynamic properties of wide type and mutation models of CFB protein. The allele-specific effect on CFB expression and its binding affinity to C3b were investigated through cell transfection and surface plasmon resonance analysis, respectively. We found that rs12614 significantly reduced the risk of IgAN (OR = 0.69, 95% CI = 0.52-0.91, P = 0.009), and the rs12614-T (R32W mutation) was correlated with lower CFB levels, higher serum C3 level, and less mesangial C3 deposition in patients with IgAN. The structural model showed that the R32W mutation reduced the structural stability of CFB protein. Furthermore, in vitro study revealed that rs12614-T decreased the expression of CFB and reduced its binding affinity to C3b by four-fold compared with rs12614-C. In conclusion, the rs12614-T in CFB was associated with low risk of IgAN probably by attenuating AP activation. [ABSTRACT FROM AUTHOR]

Background and Aims: Vascular restenosis due to neointima hyperplasia limits the long-term patency of stented arteries, resulting in angioplasty failure. The complement system has been implicated in restenosis. This study aimed to investigate the role of complement factor B (fB), an essential component of the alternative pathway of complement activation, in neointima formation., Methods: Angioplasty wire injury was conducted using 12-week-old mice deficient in fB or C9 (the main component of the membrane attacking complex, C5b-9) and littermate controls and neointima formation were assessed. Vascular smooth muscle cell (SMC) and endothelial cell (EC) proliferation and migration were examined in vitro., Results: fB was mainly detected in SMCs of stenotic arteries from humans and mice. Deletion of fB substantially reduced the neointima area and intima-to-media area ratio without affecting the media area at 28 days after injury. At 7 days after injury, fB deficiency decreased SMC proliferation, unaltering neointimal macrophage infiltration and EC reendothelialization. Vascular SMC-expressed fB, not the circulation-sourced fB, played an essential role in SMC proliferation and migration in vitro. fB deficient mice exhibited lower levels of the soluble form of C5b-9, however, deletion of C9 did not alter neointima formation after wire injury, consistent with the null impact of C9 deficiency on SMC proliferation in vitro., Conclusions: fB promotes neointima formation following wire-induced artery injury independent of forming the membrane-attacking complex. This is attributable to fB-dependent SMC proliferation and migration without affecting EC function. Targeting fB might protect against restenosis after percutaneous coronary intervention., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Objective: Dysregulation of the complement system has been described in patients with heart failure (HF). However, data on the alternative pathway are scarce and it is unknown if levels of factor B (FB) and the C3 convertase C3bBbP are elevated in these patients. We hypothesized that plasma levels of FB and C3bBbP would be associated with disease severity and survival in patients with HF. Methods: We analyzed plasma levels of FB, C3bBbP, and terminal C5b-9 complement complex (TCC) in 343 HF patients and 27 healthy controls. Results: Compared with controls, patients with HF had elevated levels of circulating FB (1.6-fold, p < 0.001) and C3bBbP (1.3-fold, p < 0.001). In contrast, TCC, reflecting the terminal pathway, was not significantly increased (p = 0.15 vs controls). FB was associated with NT-proBNP, troponin, eGFR, and i.e., C-reactive protein. FB, C3bBbP and TCC were not associated with mortality in HF during a mean follow up of 4.3 years. Conclusion: Our findings suggest that in patients with HF, the alternative pathway is activated. However, this is not accompanied by activation of the terminal pathway. [ABSTRACT FROM AUTHOR]

AIM: To evaluate whether recombinant complement factor B (CFB) short hairpin RNA (shRNA) reduces laser-induced choroidal neovascularization (CNV) in rats. METHODS: Laser-induced rat CNV model was established, and then the animals underwent fundus fluorescence angiography (FFA) and hematoxylin and eosin (HE) staining. On day 3 and 7 after photocoagulation, the expression of CFB and membrane attack complex (MAC) was detected by immunhischemistry. A recombinant CFB-shRNA plasmid was constructed. CFB and scrambled shRNA plasmids were intravenous injected into rats via the tail vein on the day of laser treatment, respectively. On day 7, the incidence of CNV was determined by FFA, and the expression of CFB and vascular endothelial growth factor (VEGF) in retinal pigment epithelium (RPE)/choroidal tissues was detected by immunhischemistry, Western blot and/or semi-quantitative reverse transcription-polymerase chain reaction (RT-PCR) in CFB and scrambled shRNA groups. The possible adverse effects of CFB-shRNA injection were assessed by transmission electron microscopy and electroretinography. RESULTS: FFA and HE results indicated that a laser-induced rat CNV model was successfully established on day 7 after photocoagulation. The expression of CFB and MAC was extremely weak in normal retina and choroid, and increased on day 3 after photocoagulation. However, it started to reduce on day 7. CFB shRNA plasmid was successfully constructed and induced CFB knockdown in the retinal and choroidal tissues. FFA showed CFB knockdown significantly inhibited incidence of CNV in rats. Moreover, CFB knockdown significantly inhibited the expression of VEGF in RPE/choroidal tissues. CFB shRNA caused no obvious side effects in eyes. CONCLUSION: CFB knockdown significantly inhibits the formation and development of CNV in vivo through reducing the expression of VEGF, which is a potential therapy target. The alternative pathway of complement activation plays an important role in CNV formation.

Immune checkpoint inhibitors (ICIs) have made an important contribution to the survival of patients with certain cancers. ICIs interrupt co-inhibitory signaling pathways mediated by programmed cell death protein 1 (PD-1), programmed cell death protein ligand 1 (PD-L1) and cytotoxic T lymphocyte-associated antigen (CTLA-4) that result in the elimination of cancer cells by stimulating the immune system. However, immune-related adverse events have also been described and attributed to an enhanced immune system activation. Recent observations have suggested a dysregulation of immune checkpoints in active antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV). We here analyzed intrarenal PD-1 and PD-L1 by immunostaining in a total of 15 kidney biopsies with ANCA-associated renal vasculitis in correlation with glomerular and tubulointerstitial lesions. For independent validation, publicly available datasets were analyzed for PD-1 expression (encoded by PDCD1). We here observed a predominant tubulointerstitial expression of PD-1 that is decreased in ANCA-associated renal vasculitis. Moreover, loss of tubulointerstitial PD-1 correlated with active ANCA-associated renal vasculitis. Consistent with the observed association with active glomerular and tubulointerstitial lesions, we identified that interstitial PD-1 correlated with tubular and/or glomerular PD-L1 positivity. Finally, PD-1 was associated with decreased local synthesis of complement factor B. Interestingly, we did not observe a correlation between PD-1 and complement C5 or its C5a receptor. Combined with our observations, this may implicate a link between impaired PD-1/PD-L1 signaling, complement factor B and active ANCA-associated renal vasculitis. These findings could be of relevance because experimental data have already described that PD-1 agonism can be used therapeutically to attenuate autoimmunity in multiple disease models. Furthermore, targeted therapy against a complement C5/C5a receptor and factor B are both available and currently evolving in the treatment of AAV. Therefore, this pilot study expands our current knowledge and describes a potential interplay between immune checkpoints and the alternative complement pathway in active ANCA-associated renal vasculitis.

ObjectiveDysregulation of the complement system has been described in patients with heart failure (HF). However, data on the alternative pathway are scarce and it is unknown if levels of factor B (FB) and the C3 convertase C3bBbP are elevated in these patients. We hypothesized that plasma levels of FB and C3bBbP would be associated with disease severity and survival in patients with HF.MethodsWe analyzed plasma levels of FB, C3bBbP, and terminal C5b-9 complement complex (TCC) in 343 HF patients and 27 healthy controls.ResultsCompared with controls, patients with HF had elevated levels of circulating FB (1.6-fold, p < 0.001) and C3bBbP (1.3-fold, p < 0.001). In contrast, TCC, reflecting the terminal pathway, was not significantly increased (p = 0.15 vs controls). FB was associated with NT-proBNP, troponin, eGFR, and i.e., C-reactive protein. FB, C3bBbP and TCC were not associated with mortality in HF during a mean follow up of 4.3 years.ConclusionOur findings suggest that in patients with HF, the alternative pathway is activated. However, this is not accompanied by activation of the terminal pathway.

Complement factor B (CFB) variants have been described to play a causative role in auto-immune associated C3 glomerulopathy (C3G) and/or atypical hemolytic uremic syndrome (aHUS) by affecting the dysregulations of alternative pathway activation. However, CFB variant concomitant with COL4A5 variant is scarce. Here, we depict two intriguing cases with concurrent novel heterozygosity for CFB c.2054_2057del (p.Ser687Profs∗16) variant and a previous reported COL4A5 c.2999G > T (p.Gly1000Val) variant in a pair of siblings. The clinical feature of either paternal CFB variant or maternal COL4A5 variant is just mild microscopic hematuria. Interestingly, their two children with paternal CFB c.2054_2057del (p.Ser687Profs∗16) variant and maternal COL4A5 c.2999G > T (p.Gly1000Val) variant presented with massive proteinuria, hematuria, and progressive renal failure with poor treatment response. Moreover, complement pathway activation in renal tissue further supports and strengthens the pathogenic role of CFB variant in the development of renal injury in the presence of COL4A5 variant. In conclusion, the rare sibling cases highlight that the extension of genetic analyses in the proband is helpful for the diagnosis and understanding of some family cluster renal diseases.

Background: The interplay between cancer cells and stromal components, including soluble mediators released from cancer cells, contributes to the progression of pancreatic ductal adenocarcinoma (PDAC). Here, we set out to identify key secreted proteins involved in PDAC progression. Methods: We performed secretome analyses of culture media of mouse pancreatic intraepithelial neoplasia (PanIN) and PDAC cells using Stable Isotope Labeling by Amino acid in Cell culture (SILAC) with click chemistry and liquid chromatography-mass spectrometry (LC-MS/MS). The results obtained were verified in primary PDAC tissue samples and cell line models. Results: Complement factor B (CFB) was identified as one of the robustly upregulated proteins, and found to exhibit elevated expression in PDAC cells compared to PanIN cells. Endogenous CFB knockdown by a specific siRNA dramatically decreased the proliferation of PDAC cells, PANC-1 and MIA PaCa-II. CFB knockdown induced increases in the number of senescence-associated-β-galactosidase (SA-β-gal) positive cells exhibiting p21 expression upregulation, which promotes cellular senescence with cyclinD1 accumulation. Furthermore, CFB knockdown facilitated downregulation of proliferating cell nuclear antigen and led to cell cycle arrest in the G1 phase in PDAC cells. Using immunohistochemistry, we found that high stromal CFB expression was associated with unfavorable clinical outcomes with hematogenous dissemination after surgery in human PDAC patients. Despite the presence of enriched CD8+ tumor infiltrating lymphocytes in the PDAC tumor microenvironments, patients with a high stromal CFB expression exhibited a significantly poorer prognosis compared to those with a low stromal CFB expression. Immunofluorescence staining revealed a correlation between stromal CFB expression in the tumor microenvironment and an enrichment of immunosuppressive regulatory T-cells (Tregs), myeloid-derived suppressor cells (MDSCs) and tumor-associated macrophages (TAMs). We also found that high stromal CFB expression showed a positive correlation with high CD8+/Foxp3+ Tregs populations in PDAC tissues. Conclusions: Our data indicate that CFB, a key secreted protein, promotes proliferation by preventing cellular senescence and is associated with immunological tumor promotion in PDAC. These findings suggest that CFB may be a potential target for the treatment of PDAC. [ABSTRACT FROM AUTHOR]

Complement factor B (CFB) variants have been described to play a causative role in auto-immune associated C3 glomerulopathy (C3G) and/or atypical hemolytic uremic syndrome (aHUS) by affecting the dysregulations of alternative pathway activation. However, CFB variant concomitant with COL4A5 variant is scarce. Here, we depict two intriguing cases with concurrent novel heterozygosity for CFB c.2054_2057del (p.Ser687Profs∗16) variant and a previous reported COL4A5 c.2999G > T (p.Gly1000Val) variant in a pair of siblings. The clinical feature of either paternal CFB variant or maternal COL4A5 variant is just mild microscopic hematuria. Interestingly, their two children with paternal CFB c.2054_2057del (p.Ser687Profs∗16) variant and maternal COL4A5 c.2999G > T (p.Gly1000Val) variant presented with massive proteinuria, hematuria, and progressive renal failure with poor treatment response. Moreover, complement pathway activation in renal tissue further supports and strengthens the pathogenic role of CFB variant in the development of renal injury in the presence of COL4A5 variant. In conclusion, the rare sibling cases highlight that the extension of genetic analyses in the proband is helpful for the diagnosis and understanding of some family cluster renal diseases. [ABSTRACT FROM AUTHOR]

Serine proteases are fundamental components of biology, including innate immunity, which is systematically orchestrated in an orderly, balanced fashion in the healthy host. Such serine proteases are found in two well-recognized pathways of an innate immune network, coagulation and complement. Both pathways, if uncontrolled due to a variety of causes, are pathogenic in numerous diseases, including coagulation disorders and infectious diseases. Previous studies have reported sequence homologies, functional similarities and interplay between these two pathways with some implications in health and disease. The current study newly reveals that complement component factor B (Bf), the second component of the alternative complement pathway, has thrombin-like activity, which is supported by a characteristic homology of the trypsin-like domain of Bf to that of thrombin. Moreover, we newly report that the trypsin-like domain of Bf is closely related to Limulus clotting factor C, the LPS sensitive clotting factor of the innate immune system. We will also discuss potential implications of our findings in diseases. • Complement factor B (Bf) has thrombin-like activity. • Trypsin-like domain of mouse Bf is homologous to those of coagulation factors of both mouse and human. • Trypsin-like domains of Bf from mouse and human are closely related to that of LPS sensitive Limulus clotting factor C. • Trypsin-like domain of Bf is conserved in the animal kingdom. • Bf involves within two networks of complement and coagulation in the immune system. [ABSTRACT FROM AUTHOR]

aHUS is a rare disease characterized by episodes of TMA that frequently progresses to CKD and often recurs after KT. The most frequent cause of aHUS is defective regulation of complement activation because of genetic anomalies. Eculizumab interrupts the process of TMA and improves renal function. We describe one female patient with aHUS who debuted in 2005 at 3‐mo‐old with extrarenal manifestations and progressed to end‐stage kidney disease (ESKD) within a year. Her family history included several affected members with similar bad outcomes. Our patient carries a strong aHUS genetic predisposition consisting in a pathogenic gain‐of‐function mutation in complement factor B concurrent with the MCP aHUS risk haplotype MCPggaac. She received a kidney transplant in 2011 without eculizumab prophylaxis. The graft, which was negative for the MCPggaac risk haplotype, had an unexpected excellent evolution without aHUS recurrence. Different retrospective studies have shown that the risk of aHUS recurrence after KT correlates well with the genetic load of aHUS risk factors. Knowing important contribution of the MCPggaac risk haplotype to the risk of developing aHUS in Factor B mutations carriers, we speculate whether the absence of this polymorphism in the graft that our patient received may have decreased the risk of aHUS recurrence after KT. [ABSTRACT FROM AUTHOR]

The underlying mechanisms of complement activation in Stargardt disease type 1 (STGD1) and age‐related macular degeneration (AMD) are not fully understood. Overaccumulation of all‐trans‐retinal (atRAL) has been proposed as the pathogenic factor in both diseases. By incubating retinal pigment epithelium (RPE) cells with atRAL, we showed that C5b‐9 membrane attack complexes (MACs) were generated mainly through complement alternative pathway. An increase in complement factor B (CFB) expression as well as downregulation of complement regulatory proteins CD46, CD55, CD59, and CFH were observed in RPE cells after atRAL treatment. Furthermore, interleukin‐1β production was provoked in both atRAL‐treated RPE cells and microglia/macrophages. Coincubation of RPE cells with interleukin‐1 receptor antagonist (IL1Ra) and atRAL ameliorated complement activation and downregulated CFB expression by attenuating both p38 and c‐Jun N‐terminal kinase (JNK) signaling pathways. Our findings demonstrate that atRAL induces an autocrine/paracrine IL‐1/IL‐1R signaling to promote complement alternative pathway activation in RPE cells and provide a novel perspective on the pathomechanism of macular degeneration. [ABSTRACT FROM AUTHOR]

Background: Numerous studies indicate a potential protective role of helminths in diabetes mellitus (DM) progression. The complement system, vital for host defense, plays a crucial role in tissue homeostasis and immune surveillance. Dysregulated complement activation is implicated in diabetic complications. We aimed to investigate the influence of the helminth, Strongyloides stercoralis (Ss) on complement activation in individuals with type 2 DM (T2D)., Methodology: We assessed circulating levels of complement proteins (C1q, C2, C3, C4, C4b, C5, C5a, and MBL (Lectin)) and their regulatory components (Factor B, Factor D, Factor H, and Factor I) in individuals with T2D with (n = 60) or without concomitant Ss infection (n = 58). Additionally, we evaluated the impact of anthelmintic therapy on these parameters after 6 months in Ss-infected individuals (n = 60)., Results: Ss+DM+ individuals demonstrated reduced levels of complement proteins (C1q, C4b, MBL (Lectin), C3, C5a, and C3b/iC3b) and complement regulatory proteins (Factor B and Factor D) compared to Ss-DM+ individuals. Following anthelmintic therapy, there was a partial reversal of these levels in Ss+DM+ individuals., Conclusion: Our findings indicate that Ss infection reduces complement activation, potentially mitigating inflammatory processes in individuals with T2D. The study underscores the complex interplay between helminth infections, complement regulation, and diabetes mellitus, offering insights into potential therapeutic avenues., Competing Interests: The authors have declared that no competing interests exist., (Copyright: This is an open access article, free of all copyright, and may be freely reproduced, distributed, transmitted, modified, built upon, or otherwise used by anyone for any lawful purpose. The work is made available under the Creative Commons CC0 public domain dedication.)

This study aims to elucidate the cellular mechanisms behind the secretion of complement factor B (CFB), known for its dual roles as an early biomarker for pancreatic ductal adenocarcinoma (PDAC) and as the initial substrate for the alternative complement pathway (ACP). Using parallel reaction monitoring analysis, we confirmed a consistent ∼2-fold increase in CFB expression in PDAC patients compared with that in both healthy donors (HD) and chronic pancreatitis (CP) patients. Elevated ACP activity was observed in CP and other benign conditions compared with that in HD and PDAC patients, suggesting a functional link between ACP and PDAC. Protein-protein interaction analyses involving key complement proteins and their regulatory factors were conducted using blood samples from PDAC patients and cultured cell lines. Our findings revealed a complex control system governing the ACP and its regulatory factors, including Kirsten rat sarcoma viral oncogene homolog ( KRAS ) mutation, adrenomedullin (AM), and complement factor H (CFH). Particularly, AM emerged as a crucial player in CFB secretion, activating CFH and promoting its predominant binding to C3b over CFB. Mechanistically, our data suggest that the KRAS mutation stimulates AM expression, enhancing CFH activity in the fluid phase through binding. This heightened AM-CFH interaction conferred greater affinity for C3b over CFB, potentially suppressing the ACP cascade. This sequence of events likely culminated in the preferential release of ductal CFB into plasma during the early stages of PDAC. (Data set ID PXD047043.).

Dengue disease is an inflammatory‐driven pathology, and complement overactivation is linked to disease severity and vascular leakage. Additionally, dysregulation of complement alternative pathway (AP) components has been described, such as upregulation of complement factor D and downregulation of complement factor H (FH), which activate and inhibit the AP, respectively. Thus, the pathology of severe dengue could in part result from AP dysfunction, even though complement and AP activation usually provide protection against viral infections. In dengue virus‐infected macrophages and endothelial cells (ECs), the site of replication and target for vascular pathology, respectively, the AP is activated. The AP activation, reduced FH and vascular leakage seen in dengue disease in part parallels other complement AP pathologies associated with FH deficiency, such as atypical haemolytic uraemic syndrome (aHUS). aHUS can be therapeutically targeted with inhibitors of complement terminal activity, raising the idea that strategies such as inhibition of complement or delivery of FH or other complement regulatory components to EC may be beneficial to combat the vascular leakage seen in severe dengue. [ABSTRACT FROM AUTHOR]

We report a case of 47-year-old male with atypical hemolytic uremic syndrome (aHUS). He had low C3 levels and whole exome sequencing revealed heterozygous missense novel variation in exon 8 of the gene encoding complement factor B (CFB), leading to substitution of leucine for proline at codon 369 (c.1106C>T; p.Pro369Leu). Following plasma exchanges and hemodialysis, the patient achieved hematological remission and became dialysis independent. [ABSTRACT FROM AUTHOR]

The role of complement system in heart diseases is controversial. Besides, the mechanisms by which complement components participate in cardiac remodeling (CR) and heart failure during uremia are unclear. In this study, 5/6 nephrectomy was performed to adult mice to establish the uremic model and CR deteriorated over the course of uremia. Although complement pathways were not further activated over the course of the disease, soluble complement factor B (CFB) was upregulated at post‐nephrectomy day 90 (PNx90) compared with PNx30. Further, CFB notably deteriorated CR in uremic mice but this effect was reversed by depletion of macrophages with liposomal clodronate. In vivo and in vitro CFB upregulated arginase 1 (ARG1) expression, increased ARG1 enzymatic activity, and stimulated the syntheses of ornithine, leading to polyamine overproduction in macrophages. Putrescine, an important polyamine, promoted cardiac fibroblast proliferation and collagen production, resulting in progressive CR. In vivo the inhibition of ARG1 activity with Nω‐hydroxyl‐l‐arginine remarkably improved the general survival rates, inhibited the infiltration of cardiac fibroblasts, and alleviated progression of CR in uremic mice. Taken together, the CFB‒ARG1‒putrescine axis is related to progression of CR and ARG1 hyperactivity in macrophages may provide a novel therapeutic target against the heart injury in uremia. [ABSTRACT FROM AUTHOR]

BackgroundAge-related maculopathy (ARM) is a common cause of visual impairment in the elderly populations of industrialized countries and significantly affects the quality of life of those suffering from the disease. Variants within two genes, the complement factor H (CFH) and the poorly characterized LOC387715 (ARMS2), are widely recognized as ARM risk factors. CFH is important in regulation of the alternative complement pathway suggesting this pathway is involved in ARM pathogenesis. Two other complement pathway genes, the closely linked complement component receptor (C2) and complement factor B (CFB), were recently shown to harbor variants associated with ARM.Methods/principal findingsWe investigated two SNPs in C2 and two in CFB in independent case-control and family cohorts of white subjects and found rs547154, an intronic SNP in C2, to be significantly associated with ARM in both our case-control (P-value 0.00007) and family data (P-value 0.00001). Logistic regression analysis suggested that accounting for the effect at this locus significantly (P-value 0.002) improves the fit of a genetic risk model of CFH and LOC387715 effects only. Modeling with the generalized multifactor dimensionality reduction method showed that adding C2 to the two-factor model of CFH and LOC387715 increases the sensitivity (from 63% to 73%). However, the balanced accuracy increases only from 71% to 72%, and the specificity decreases from 80% to 72%.Conclusions/significanceC2/CFB significantly influences AMD susceptibility and although accounting for effects at this locus does not dramatically increase the overall accuracy of the genetic risk model, the improvement over the CFH-LOC387715 model is statistically significant.

Complement factor B (CFB), a 95-kDa protein, is a crucial catalytic element of the alternative pathway (AP) of complement. After binding of CFB to C3b, activation of the AP depends on the proteolytic cleavage of CFB by factor D to generate the C3 convertase (C3bBb). The C3 convertase contains the catalytic subunit of CFB (Bb), the enzymatic site for the cleavage of a new molecule of C3 into C3b. In addition to its role in activating the AP, CFB has been implicated in pathological ocular neovascularization, a common feature of several blinding eye diseases, however, with somewhat conflicting results. The focus of this study was to investigate the direct impact of CFB on ocular neovascularization in a tightly controlled environment. Using mouse models of laser-induced choroidal neovascularization (CNV) and oxygen-induced retinopathy (OIR), our study demonstrated an increase in CFB expression during pathological angiogenesis. Results from several in vitro and ex vivo functionality assays indicated a promoting effect of CFB in angiogenesis. Mechanistically, CFB exerts this pro-angiogenic effect by mediating the vascular endothelial growth factor (VEGF) signaling pathway. In summary, we demonstrate compelling evidence for the role of CFB in driving ocular angiogenesis in a VEGF-dependent manner. This work provides a framework for a more in-depth exploration of CFB-mediated effects in ocular angiogenesis in the future.

Background: C3 glomerulopathy is a recently described entity classified as complementassociated glomerular disease. Case Presentation: We report a case of a 48-year-old man referred to the nephrology department for nephrotic syndrome with rapidly progressive kidney failure, acquired partial lipodystrophy and drusen in Bruch’s membrane of the retina. Blood tests showed low C3 and no evidence for autoimmune diseases, monoclonal gammopathy or infection. The renal biopsy revealed a proliferative endocapillary and crescentic glomerulonephritis with glomerular deposits exclusively of C3 and significant interstitial fibrosis. The electronic microscopy was consistent with dense deposit disease. The complement analysis revealed a pathogenic mutation of the complement factor B (CFB) gene not previously described in literature. Conclusions: The authors report a new mutation of CFB, in a dense deposit disease patient; this finding brings a new insight to the pathogenic pathway of C3 glomerulopathy and possibly to other complement dysregulation associated glomerular diseases. More clinical trials are needed to clarify both the pathogenicity and the optimal treatment for these entities.

Age-related macular degeneration (AMD) is the leading cause of irreversible vision loss among the elderly in the developed world. Whilst AMD is a multifactorial disease, the involvement of the complement system in its pathology is well documented, with single-nucleotide polymorphisms (SNPs) in different complement genes representing an increased risk factor. With several complement inhibitors explored in clinical trials showing limited success, patients with AMD are still without a reliable treatment option. This indicates that there is still a gap of knowledge in the functional implications and manipulation of the complement system in AMD, hindering the progress towards translational treatments. Since the discovery of the CRISPR/Cas system and its development into a powerful genome engineering tool, the field of molecular biology has been revolutionised. Genetic variants in the complement system have long been associated with an increased risk of AMD, and a variety of haplotypes have been identified to be predisposing/protective, with variation in complement genes believed to be the trigger for dysregulation of the cascade leading to inflammation. AMD-haplotypes (SNPs) alter specific aspects of the activation and regulation of the complement cascade, providing valuable insights into the pathogenic mechanisms of AMD with important diagnostic and therapeutic implications. The effect of targeting these AMD-related SNPs on the regulation of the complement cascade has been poorly explored, and the CRISPR/Cas system provides an ideal tool with which to explore this avenue. Current research concentrates on the association events of specific AMD-related SNPs in complement genes without looking into the effect of targeting these SNPs and therefore influencing the complement system in AMD pathogenesis. This review will explore the current understanding of manipulating the complement system in AMD pathogenesis utilising the genomic manipulation powers of the CRISPR/Cas systems. A number of AMD-related SNPs in different complement factor genes will be explored, with a particular emphasis on factor H (C FH ), factor B (C FB ), and complement C3 ( C3 ).

Mesangial complement C3 deposits, reflecting alternative and possibly lectin pathway activation, are characteristic in biopsies of patients with IgA nephropathy (IgAN). A recent randomized controlled trial tested the efficacy and safety of iptacopan, a factor B inhibitor, in patients with IgAN. Iptacopan dose-dependently reduced proteinuria, and there was a pronounced decrease of urinary C5b-9. This offers the perspective of "personalizing" therapy, which would be a unique feature of this novel approach to IgAN. A phase III clinical trial (APPLAUSE-IgAN) is ongoing., (Copyright © 2023 International Society of Nephrology. Published by Elsevier Inc. All rights reserved.)

Background: C3 glomerulopathy is a recently described entity classified as complementassociated glomerular disease. Case Presentation: We report a case of a 48-year-old man referred to the nephrology department for nephrotic syndrome with rapidly progressive kidney failure, acquired partial lipodystrophy and drusen in Bruch's membrane of the retina. Blood tests showed low C3 and no evidence for autoimmune diseases, monoclonal gammopathy or infection. The renal biopsy revealed a proliferative endocapillary and crescentic glomerulonephritis with glomerular deposits exclusively of C3 and significant interstitial fibrosis. The electronic microscopy was consistent with dense deposit disease. The complement analysis revealed a pathogenic mutation of the complement factor B (CFB) gene not previously described in literature. Conclusions: The authors report a new mutation of CFB, in a dense deposit disease patient; this finding brings a new insight to the pathogenic pathway of C3 glomerulopathy and possibly to other complement dysregulation associated glomerular diseases. More clinical trials are needed to clarify both the pathogenicity and the optimal treatment for these entities. [ABSTRACT FROM AUTHOR]

BACKGROUND: For patients with pancreatic cancer, a preoperative assessment of prognosis is crucial to predict cancer recurrence and to prepare a postoperative adjuvant strategy and appropriate patient-counsel. OBJECTIVE: We evaluated the prognostic predictive power of complement factor B (CFB) by comparing it to that of other known tumor markers in resected pancreatic cancer patients. METHODS: From 2012 to 2013 period, we retrospectively reviewed the plasma CFB levels of 35 pancreatic cancer patients. The patients were divided into two groups according to serologic CFB values. Disease-free survival (DFS) and overall survival (OS) rates were analyzed. RESULTS: Based on the cut-off values of plasma CFB, 15 patients were placed in the low CFB group and the other 20 patients were placed in the high CFB group. There was a significant difference in DFS between the two groups (Low CFB vs. High CFB: 36.9 months vs. 13.9 months, p : 0.007). In the OS analysis, there was also a significant difference in the survival rates of the two groups (Low CFB vs. High CFB: 49.7 months vs. 29.0 months, p : 0.048). CONCLUSION: Preoperative plasma CFB can be used to predict the prognosis of resectable pancreatic cancers; it outperforms both CA 19-9 and CEA. [ABSTRACT FROM AUTHOR]