Activation of the classical complement pathway in myasthenia gravis with acetylcholine receptor antibodies.

INTRODUCTION/AIMS: Myasthenia gravis (MG) is an autoimmune disease affecting the neuromuscular junction (NMJ) of skeletal muscle. Complement activation is one of the mechanisms by which anti-acetylcholine receptor (anti-AChR) autoantibodies reduce synaptic transmission at the NMJ. In this study, we aimed to examine the activation of the complement pathways, including the classical pathway, as potential contributors to the pathogenesis of MG with anti-AChR antibodies. METHODS: In this single-center, observational study of 45 patients with anti-AChR-antibody-positive generalized MG, serum concentrations of major components of the complement pathways, including C1q, C5, C5a, soluble C5b-9 (sC5b-9), Ba, and complement factor H, were measured using an enzyme-linked immunosorbent assay. A total of 25 patients with a non-inflammatory neurological disorder served as controls. In addition, the relationships of complement activation with clinical characteristics were examined. RESULTS: The patients with MG exhibited lower serum levels of C5 (p = .0001) and higher serum levels of sC5b-9 (p = .004) compared with the control group. At about 6 months (range, 172-209 days) after the start of immunotherapy, serum levels of Ba were significantly higher than baseline levels (p = .002) and were associated with improvement in MG clinical scores. DISCUSSION: Herein, we provide evidence for the activation of the classical complement pathway and its association with disease activity in anti-AChR-antibody-positive generalized MG.

Peritoneal Expression of Membrane Complement Regulators Is Decreased in Peritoneal Dialysis Patients with Infected Peritonitis.

In peritoneal dialysis (PD) patients, fungi and Pseudomonas aeruginosa are considered important causative microorganisms for peritonitis with poor prognosis. Our objective was to explore expressions of membrane complement (C) regulators (CRegs) and tissue injuries in the peritoneum of patients with PD-related peritonitis, including fungal and Pseudomonas aeruginosa peritonitis. In peritoneal biopsy tissues obtained at PD catheter removal, we investigated the severity of peritonitis-associated peritoneal injuries and the expression of CRegs, CD46, CD55, and CD59 against peritoneal tissues without any episode of peritonitis. In addition, we evaluated peritoneal injuries among fungal and Pseudomonas aeruginosa-peritonitis (P1) and Gram-positive bacterial peritonitis (P2). We also observed deposition of C activation products such as activated C and C5b-9 and measured sC5b-9 in the PD fluid of patients. As a result, the severity of peritoneal injuries correlated inversely with the expression of peritoneal CRegs. Peritoneal CReg expression in peritonitis was significantly reduced compared to no peritonitis. Peritoneal injuries were more severe in P1 than in P2. CReg expression was further decreased and C5b-9 further increased in P1 than in P2. In conclusion, severe peritoneal injuries due to fungal and Pseudomonas aeruginosa-peritonitis decreased CReg expression and increased deposition of activated C3 and C5b-9 in the peritoneum, suggesting that peritonitis, particularly fungal and Pseudomonas aeruginosa-peritonitis, might induce susceptibility to further peritoneal injuries due to excessive C activation.

[Various phenotypes of postpartum atypical hemolytic uremic syndrome: the role of genetic testing in determining prognosis. Case report].

We report a case of atypical hemolytic uremic syndrome (aHUS) that occurred after childbirth in a patient with a history of numerous recurrent episodes of TMA with nephrotic proteinuria and impaired renal function. At 33 weeks of the first spontaneous pregnancy, proteinuria up to 0.8 g/l was first registered, at 38 weeks she was hospitalized with proteinuria, reaching a maximum of 13 g/l, she was delivered promptly, after which progressive thrombocytopenia was noted over the next few days (up to 44×109/l) and anemia and severe arterial hypertension, which could not be corrected by several groups of antihypertensive drugs. Initiated plasma therapy had no effect. After exclusion of all other causes of TMA, therapy with eculizumab was initiated, which made it possible to quickly and completely stop the phenomena of TMA. The presented observation demonstrates the successful treatment of recurrent course of aHUS with eculizumab with the achievement of complete recovery of kidney function in a patient with a homozygous mutation in the MCP gene. It is worth noting the importance of genetic research even in those situations where clinically aHUS is beyond doubt.

Complement regulation and kidney diseases: recent knowledge of the double-edged roles of complement activation in nephrology.

The complement activation system plays important roles to maintain homeostasis in the host and to fight foreign invaders to protect the host. Therefore, the complement system is considered a core part of innate immunity which also cross-talks to acquired immunity. In the history of nephrology, the complement system is familiar to us, because complement protein or fragment deposition, including C3, C4, C1q, and/or C4d, is routinely estimated by immunohistochemistry to diagnose renal pathologies. The relationships between pathological mechanisms and complement activation have been investigated for renal diseases such as post-infectious glomerulonephritis, lupus nephritis, and primary membranoproliferative glomerulonephritis, which are usually accompanied by hypocomplementemia. However, unregulated complement activation in local areas might be associated with progression of various renal injuries even in the normocomplementemic patient. Recently, attention has focused on dysfunction of complement regulation in various diseases including renal diseases such as atypical hemolytic uremic syndrome and C3 glomerulopathy. Some mechanisms associated with complement activation in these diseases were clarified. In addition, lots of anti-complement agents were developed and some of the agents have become clinically available. Now, anti-complement therapies represent a realistic choice of therapeutic approaches for complement-related diseases. Research on roles of complement activation is proceeding into new stages in the field of nephrology and in other fields involving both basic and clinical research. We herein summarize relationships between the complement activation and regulation systems, their physiological effects and roles in maintenance of homeostasis in the host, and how dysregulation of the complement system triggers disease, especially renal disease.

CD59 association with infectious bronchitis virus particles protects against antibody-dependent complement-mediated lysis.

CD59 protein functions as a negative regulator of the terminal pathway of the complement system by binding to the C8/C9 factors. To date, little is known about the role of CD59 in coronavirus infectious bronchitis virus (IBV) infection. In this study, we discovered that CD59 was downregulated in IBV-infected cells and was associated with IBV virions. This association protected IBV particles from antibody-dependent complement-mediated lysis. IBV titres in the supernatant were significantly increased when CD59 proteins were overexpressed in cells followed by IBV infection, and this observation was further supported by knockdown or cleavage of CD59. Because no considerable change in IBV N protein and viral RNA levels was detected in total cell lysates prepared from the overexpression, knockdown or cleavage of CD59 groups, our data indicated that CD59 was involved in IBV particle release and that IBV had evolved a mechanism to utilize CD59 to evade complement-mediated destruction.

CD55 Variant Associated with Pegylated-interferon α Therapy Response in HBeAg-positive Chronic Hepatitis B Patients.

Background and Aims: Only a small percentage of chronic hepatitis B (CHB) patients effectively respond to treatment with pegylated-interferon alpha (PegIFNα) or nucleos(t)ide analogues (NUCs). We aimed to detect the correlations of complement regulators-associated single-nucleotide polymorphisms (SNPs) with treatment response of hepatitis B e antigen (HBeAg)-positive CHB patients. Methods: A total of 1,763 HBeAg-positive CHB patients were enrolled, 894 received PegIFNα for at least 48 weeks and were followed up for 24 weeks, and 869 received NUCs for 104 weeks. For each patient, nine SNPs in genes encoding for complement regulators were determined and genotyped. To assess the cumulative effect of numerous SNPs, a polygenic score (PGS) was utilized. The correlations of SNPs and PGS with the levels of combined response (CR) and hepatitis B s antigen (HBsAg) loss were also investigated. Results: In PegIFNα-treated patients, an intronic SNP of CD55, rs28371597, was strongly related to CR, and the CR rate in rs28371597_GG genotype carriers was only approximately half that of rs28371597_GT/TT genotype carriers (20.29% vs. 37.10%, p=2.00 × 10-3). A PGS incorporating CD55_rs28371597 and two additional SNPs, CFB_rs12614 and STAT4_rs7574865, which had been considered as predictors for PegIFNα treatment response before, was strongly correlated with the levels of CR (p-trend=7.94×10-6) and HBsAg loss (p-trend=9.40×10-3) in PegIFNα-treated patients. In NUCs-treated individuals, however, none of the nine SNPs were shown to be significantly linked to CHB treatment response. Conclusions: CD55_rs28371597 is a promising biomarker for predicting CHB patients' responsiveness to PegIFNα therapy. The updated PGS may be used for optimizing CHB treatment.

Long-term peritoneal dialysate exposure modulates expression of membrane complement regulators in human peritoneal mesothelial cells.

The membrane complement regulators (CRegs) CD46, CD55, and CD59 are highly expressed on human peritoneal mesothelial cells. However, how mesothelial CRegs change according to the peritoneal dialysis (PD) history of patients has remained unclear. We therefore examined longitudinal changes in CRegs in primary cultured mesothelial cells from PD patients (human peritoneal mesothelial cells; HPMCs) and examined which components of PD fluid (PDF) affect CRegs in vitro. We measured levels of soluble C5b-9 in overnight-dwelling PDF in PD patients and also evaluated changes in CRegs expression on HPMCs collected from PDF using flow cytometry and polymerase chain reaction at a 1-year interval of PD therapy. We also evaluated changes in CReg expressions with stimulation by each component of PDF (glucose, lactic acid and pH) using the Met5A human mesothelial cell line. Levels of sC5b-9 in PDF decreased significantly during 1 year, while expressions of CD46 and CD59 proteins and mRNAs increased significantly in HPMCs during 1 year. Analyzing Met-5A cells, we observed that expressions of the three CRegs were increased by glucose and lactic acid in a concentration-dependent manner, but conversely that expressions of CRegs were decreased by lower pH stimulation. History of PD might influence expression of CRegs by HPMCs through properties of PDF such as glucose, lactic acid, and pH. These results suggest that mesothelial cells may alter expression of CRegs for the purpose of protecting the peritoneum and the presence of PDF might affect peritoneal homeostasis associated with the complement system.

Quantification of Factor H Mediated Self vs. Non-self Discrimination by Mathematical Modeling.

The complement system is part of the innate immune system and plays an important role in the host defense against infectious pathogens. One of the main effects is the opsonization of foreign invaders and subsequent uptake by phagocytosis. Due to the continuous default basal level of active complement molecules, a tight regulation is required to protect the body's own cells (self cells) from opsonization and from complement damage. A major complement regulator is Factor H, which is recruited from the fluid phase and attaches to cell surfaces where it effectively controls complement activation. Besides self cells, pathogens also have the ability to bind Factor H; they can thus escape opsonization and phagocytosis causing severe infections. In order to advance our understanding of the opsonization process at a quantitative level, we developed a mathematical model for the dynamics of the complement system-termed DynaCoSys model-that is based on ordinary differential equations for cell surface-bound molecules and on partial differential equations for concentration profiles of the fluid phase molecules in the environment of cells. This hybrid differential equation approach allows to model the complement cascade focusing on the role of active C3b in the fluid phase and on the cell surface as well as on its inactivation on the cell surface. The DynaCoSys model enables us to quantitatively predict the conditions under which Factor H mediated complement evasion occurs. Furthermore, investigating the quantitative impact of model parameters by a sensitivity analysis, we identify the driving processes of complement activation and regulation in both the self and non-self regime. The two regimes are defined by a critical Factor H concentration on the cell surface and we use the model to investigate the differential impact of complement model parameters on this threshold value. The dynamic modeling on the surface of pathogens are further relevant to understand pathophysiological situations where Factor H mutants and defective Factor H binding to target surfaces results in pathophysiology such as renal and retinal disease. In the future, this DynaCoSys model will be extended to also enable evaluating treatment strategies of complement-related diseases.

Complements are involved in alcoholic fatty liver disease, hepatitis and fibrosis.

The complement system is a key component of the body's immune system. When abnormally activated, this system can induce inflammation and damage to normal tissues and participate in the development and progression of a variety of diseases. In the past, many scholars believed that alcoholic liver disease (ALD) is induced by the stress of ethanol on liver cells, including oxidative stress and dysfunction of mitochondria and protease bodies, causing hepatocyte injury and apoptosis. Recent studies have shown that complement activation is also involved in the genesis and development of ALD. This review focuses on the roles of complement activation in ALD and of therapeutic intervention in complement-activation pathways. We intend to provide new ideas on the diagnosis and treatment of ALD.

CD59 polymorphisms are associated with gene expression and different sexual susceptibility to pemphigus foliaceus.

Pemphigus foliaceus (PF) is an autoimmune disease, endemic in Brazilian rural areas, characterized by acantholysis and accompanied by complement activation, with generalized or localized distribution of painful epidermal blisters. CD59 is an essential complement regulator, inhibiting formation of the membrane attack complex, and mediating signal transduction and activation of T lymphocytes. CD59 has different transcripts by alternative splicing, of which only two are widely expressed, suggesting the presence of regulatory sites in their noncoding regions. To date, there is no association study with polymorphisms in CD59 noncoding regions and susceptibility to autoimmune diseases. In this study, we aimed to evaluate if CD59 polymorphisms have a possible regulatory effect on gene expression and susceptibility to PF. Six noncoding polymorphisms were haplotyped in 157 patients and 215 controls by sequence-specific PCR, and CD59 mRNA levels were measured in 82 subjects, by qPCR. The rs861256-allele-G (rs861256*G) was associated with increased mRNA expression (p = .0113) and PF susceptibility in women (OR = 4.11, p = .0001), which were also more prone to develop generalized lesions (OR = 4.3, p = .009) and to resist disease remission (OR = 3.69, p = .045). Associations were also observed for rs831625*G (OR = 3.1, p = .007) and rs704697*A (OR = 3.4, p = .006) in Euro-Brazilian women, and for rs704701*C (OR = 2.33, p = .037) in Afro-Brazilians. These alleles constitute the GGCCAA haplotype, which also increases PF susceptibility (OR = 4.9, p = .045) and marks higher mRNA expression (p = .0025). In conclusion, higher CD59 transcriptional levels may be related with PF susceptibility (especially in women), probably due to the effect of genetic polymorphism and to the CD59 role in T cell signal transduction.

Hide and Seek: How Lyme Disease Spirochetes Overcome Complement Attack.

Overcoming the first line of the innate immune system is a general hallmark of pathogenic microbes to avoid recognition and to enter the human host. In particular, spirochetes belonging to the Borrelia burgdorferi sensu lato complex have developed various means to counter the immune response and to successfully survive in diverse host environments for a prolonged period of time. In regard to complement resistance, Borrelia utilize a plethora of immune evasion strategies involves capturing of host-derived complement regulators, terminating complement activation as well as shedding of cell-destroying complement complexes to manipulate and to expeditiously inhibit human complement. Owing to their mode of action, the interacting surface-exposed proteins identified among B. burgdorferi sensu stricto (s.s.), Borrelia afzelii, Borrelia spielmanii, and Borrelia bavariensis can be classified into at least two major categories, namely, molecules that directly interfere with distinct complement components including BBK32, CspA, BGA66, BGA71, and a CD59-like protein or molecules, which indirectly counteract complement activation by binding various complement regulators such as Factor H, Factor H-like protein 1 (FHL-1), Factor H-related proteins FHR-1, FHR-2, or C4Bp. The latter group of genetically and structurally unrelated proteins has been collectively referred to as "complement regulator-acquiring surface proteins" and consists of CspA, CspZ, ErpA, ErpC, ErpP, and the as yet unidentified protein p43. This review focuses on the current knowledge of immune evasion mechanisms exhibited by Lyme disease spirochetes and highlights the role of complement-interfering, infection-associated molecules playing an important part in these processes. Deciphering the immune evasion strategies may provide novel avenues for improved diagnostic approaches and therapeutic interventions.

Cd59a deficiency in mice leads to preferential innate immune activation in the retinal pigment epithelium-choroid with age.

Dysregulation of the complement system has been implicated in the pathogenesis of age-related macular degeneration. To investigate consequences of altered complement regulation in the eye with age, we examined Cd59a complement regulator deficient (Cd59a(-/-)) mice between 4 and 15 months. In vivo imaging revealed an increased age-related accumulation of autofluorescent spots in Cd59a(-/-) mice, a feature that reflects accumulation of subretinal macrophages and/or microglia. Despite this activation of myeloid cells in the eye, Cd59a(-/-) mice showed normal retinal histology and function as well as normal choroidal microvasculature. With age, they revealed increased expression of activators of the alternative complement pathway (C3, Cfb, Cfd), in particular in the retinal pigment epithelium (RPE)-choroid but less in the retina. This molecular response was not altered by moderately-enhanced light exposure. Cd59a deficiency therefore leads to a preferential age-related dysregulation of the complement system in the RPE-choroid, that alone or in combination with light as a trigger, is not sufficient to cause choroidal vascular changes or retinal degeneration and dysfunction. This data emphasizes the particular vulnerability of the RPE-choroidal complex to dysregulation of the alternative complement pathway during aging.