Endothelial dysfunction and complement activation are independently associated with disease duration in patients with systemic vasculitis.

OBJECTIVES: Systemic vasculitis is a heterogenous group of autoimmune diseases characterized by enhanced cardiovascular mortality. Endothelial dysfunction is associated with accelerated vascular damage, representing a core pathophysiologic mechanism contributing to excess CV risk. Recent studies have also shown that complement activation holds significant role in the pathogenesis of Anti-Neutrophilic Cytoplasmic Autoantibody (ANCA) -associated vasculitis (AAV). Given the potential crosstalk between the endothelium and complement, we aimed to assess, for the first time simultaneously, easily accessible biomarkers of endothelial dysfunction and complement activation in SV. METHODS: We measured circulating endothelial microvesicles (EMVs) and soluble complement components representative of alternative, classical and terminal activation (C5b-9, C1q, Bb fragments, respectively) in a meticulously selected group of patients with systemic vasculitis, but without cardiovascular disease. Individuals free from systemic diseases, who were matched with patients for cardiovascular risk factors(hypertension, diabetes, smoking, dyslipidemia), comprised the control group. RESULTS: We studied 60 individuals (30 in each group). Patients with systemic vasculitis had elevated EMVs, higher levels of C5b-9 [536.4(463.4) vs 1200.94457.3), p = 0.003] and C1q [136.2(146.5 vs 204.2(232.9), p = 0.0129], compared to controls [232.0 (243.5) vs 139.3(52.1), p < 0.001]. In multivariate analysis both EMVs and C5b-9 were independently associated with disease duration (p = 0.005 and p = 0.004 respectively), yet not with disease activity. CONCLUSION: Patients with systemic vasculitis exhibit impaired endothelial function and complement activation, both assessed by easily accessible biomarkers, even in the absence of cardiovascular disease manifestations. EMVs and soluble complement components such as C5b-9 and C1q could be used as early biomarkers of endothelial dysfunction and complement activation, respectively, in clinical practice during the course of SV, yet their predictive value in terms of future cardiovascular disease warrants further verification in appropriately designed studies.

[The complement cascade in renal pathology]. / Die Komplementkaskade in der Nierenpathologie.

The complement cascade comprises a variety of soluble and cell surface proteins and is an important component of the innate immune system. When the cascade is triggered by any of the three activation pathways, the complement system rapidly produces large amounts of protein fragments that are potent mediators of inflammatory, vasoactive, and metabolic responses. All activation pathways lead to the terminal complement cascade with the formation of the membrane attack complex, which lyses cells by forming membrane pores. Although the complement system is essential for pathogen defense and homeostasis, excessive or uncontrolled activation can lead to tissue damage. Recent research shows that the complement system is activated in almost all kidney diseases, even those not traditionally considered immune-mediated. In directly complement-mediated kidney diseases, complement factors or regulators are defective, afunctional or inactivated by antibodies. In many other renal diseases, the complement system is activated secondarily as a result of renal damage and is therefore involved in the pathogenesis of the disease, but is not the trigger. The detection of complement deposits is also used to diagnose kidney disease. This review describes the structure of the complement system and the effects of its dysregulation as a cause and modulator of renal disease.

Humanization of a mouse anti-human complement C6 monoclonal antibody as a potential therapeutic for certain complement-mediated diseases.

The assembly of tissue-damaging membrane attack complexes (MACs; C5b-9) is a major mechanism by which excessive complement activation causes diseases. We previously developed a mouse anti-human C6 monoclonal antibody (mAb) 1C9 that selectively inhibits the assembly of MACs in human and non-human primates. In this project, we found that 1C9 also cross-reacted with rat and guinea pig C6, and determined its binding domains on C6 using different truncated C6 proteins. We then humanized the anti-C6 mAb by molecular modeling and complementarity-determining region grafting. After screening a library of 276 humanized variants with different combinations of humanized light and heavy chains in biophysical assays, we identified clone 3713 with the best developability profile, and an increased affinity against C6 when compared with the parental 1C9 mAb. This humanized 3713 mAb inhibited human, monkey, and rat complement-mediated hemolysis in vitro, and more importantly, it significantly reduced complement-mediated hemolysis in vivo in rats. These results demonstrated the successful humanization of the anti-C6 mAb and suggested that the humanized 3713 mAb could be further developed as a new therapeutic that selectively targets MAC for certain complement-mediated pathological conditions.

The Inflammatory Response Induced by Aspergillus fumigatus Conidia Is Dependent on Complement Activation: Insight from a Whole Blood Model.

INTRODUCTION: We aimed to elucidate the inflammatory response of Aspergillus fumigatus conidia in a whole-blood model of innate immune activation and to compare it with the well-characterized inflammatory reaction to Escherichia coli. METHODS: Employing a human lepirudin whole-blood model, we analyzed complement and leukocyte activation by measuring the sC5b-9 complex and assessing CD11b expression. A 27-multiplex system was used for quantification of cytokines. Selective cell removal from whole blood and inhibition of C3, C5, and CD14 were also applied. RESULTS: Our findings demonstrated a marked elevation in sC5b-9 and CD11b post-A. fumigatus incubation. Thirteen cytokines (TNF, IL-1ß, IL-1ra, IL-4, IL-6, IL-8, IL-17, IFNγ, MCP-1, MIP-1α, MIP-1ß, FGF-basic, and G-CSF) showed increased levels. A generally lower level of cytokine release and CD11b expression was observed with A. fumigatus conidia than with E. coli. Notably, monocytes were instrumental in releasing all cytokines except MCP-1. IL-1ra was found to be both monocyte and granulocyte-dependent. Pre-inhibiting with C3 and CD14 inhibitors resulted in decreased release patterns for six cytokines (TNF, IL-1ß, IL-6, IL-8, MIP-1α, and MIP-1ß), with minimal effects by C5-inhibition. CONCLUSION: A. fumigatus conidia induced complement activation comparable to E. coli, whereas CD11b expression and cytokine release were lower, underscoring distinct inflammatory responses between these pathogens. Complement C3 inhibition attenuated cytokine release indicating a C3-level role of complement in A. fumigatus immunity.

Different Complement Activation Patterns Following C5 Cleavage in MOGAD and AQP4-IgG+NMOSD.

OBJECTIVES: In myelin oligodendrocyte glycoprotein IgG-associated disease (MOGAD) and aquaporin-4 IgG+ neuromyelitis optica spectrum disorder (AQP4+NMOSD), the autoantibodies are mainly composed of IgG1, and complement-dependent cytotoxicity is a primary pathomechanism in AQP4+NMOSD. We aimed to evaluate the CSF complement activation in MOGAD. METHODS: CSF-C3a, CSF-C4a, CSF-C5a, and CSF-C5b-9 levels during the acute phase before treatment in patients with MOGAD (n = 12), AQP4+NMOSD (n = 11), multiple sclerosis (MS) (n = 5), and noninflammatory neurologic disease (n = 2) were measured. RESULTS: CSF-C3a and CSF-C5a levels were significantly higher in MOGAD (mean ± SD, 5,629 ± 1,079 pg/mL and 2,930 ± 435.8 pg/mL) and AQP4+NMOSD (6,017 ± 3,937 pg/mL and 2,544 ± 1,231 pg/mL) than in MS (1,507 ± 1,286 pg/mL and 193.8 ± 0.53 pg/mL). CSF-C3a, CSF-C4a, and CSF-C5a did not differ between MOGAD and AQP4+NMOSD while CSF-C5b-9 (membrane attack complex, MAC) levels were significantly lower in MOGAD (17.4 ± 27.9 ng/mL) than in AQP4+NMOSD (62.5 ± 45.1 ng/mL, p = 0.0019). Patients with MOGAD with severer attacks (Expanded Disability Status Scale [EDSS] ≥ 3.5) had higher C5b-9 levels (34.0 ± 38.4 ng/m) than those with milder attacks (EDSS ≤3.0, 0.9 ± 0.7 ng/mL, p = 0.044). DISCUSSION: The complement pathway is activated in both MOGAD and AQP4+NMOSD, but MAC formation is lower in MOGAD, particularly in those with mild attacks, than in AQP4+NMOSD. These findings may have pathogenetic and therapeutic implications in MOGAD.

Mechanism of Humoral and Cellular Immune Modulation Provided by Porcine Sertoli Cells

The understanding of main mechanisms that determine the ability of immune privilege related to Sertoli cells (SCs) will provide clues for promoting a local tolerogenic environment. In this study, we evaluated the property of humoral and cellular immune response modulation provided by porcine SCs. Porcine SCs were resistant to human antibody and complement-mediated formation of the membrane attack complex (38.41+/-2.77% vs. 55.02+/-5.44%, p=0.027) and cell lysis (42.95+/-1.75% vs. 87.99 +/-2.25%, p<0.001) compared to immortalized aortic endothelial cells, suggesting that porcine SCs are able to escape cellular lysis associated with complement activation by producing one or more immunoprotective factors that may be capable of inhibiting membrane attack complex formation. On the other hand, porcine SCs and their culture supernatant suppressed the up-regulation of CD40 expression (p<0.05) on DCs in the presence of LPS stimulation. These novel findings, as we know, suggest that immune modulatory effects of porcine SCs in the presence of other antigen can be obtained from the first step of antigen presentation. These might open optimistic perspectives for the use of porcine SCs in tolerance induction eliminating the need for chronic immunosuppressive drugs.

How Schistosoma mansoni evades complement-mediated immune attack

Schistosoma mansoni is a trematode that parasitizes man and other mammals, surviving in the vertebrate host for decades, despite eliciting a strong cellular and humoral immune response. The mechanism by which S. mansoni evades immune attack, even in the presence of specific antischistosome antibodies and complement has been the object of perplexity. It was originally proposed that schistosomes avoid antibody recognition by masking themselves with host antigens, and erythrocyte-derived molecules have been appointed as playing this role. We have discovered that schistosomula become complement-resistant by incorporating into their surface a complement inhibitory molecule released from human erythrocytes (HuE). This molecule was shown to be the decay-accelerating factor (DAF), a 70 kDa protein tethered to the surface of HuE by a glycosylphosphatidylinositol (GPI) anchor. The mechanism by which schistosomula acquire DAF from the surface of HuE and its importance to the survival of S.mansoni in the host are discussed.

El sistema del complemento sérico: parte 1, mecanismos de reacción y efectos biológicos / The serum complement system: part1, activation mechanisms and biological effects

A un siglo de su descubrimiento por Bordet, se trata de poner un poco de orden en los mecanismos de activación del complemento a través de su hasta ahora conocidas rutas de activación clásica o de C1 y la vía alterna o de la properdina. Se hace además referencia a otras vías de activación descritas más recientemente como la activación iniciada por la lectina de unión a la manosa (MBL). Se destaca también la actividad de los componentes inhibidores o controladores, que frenan la actividad del sistema, evitando la producción de daños por la formación y liberación de péptidos con potente acción biológica derivados del mismo, tal el caso de las anafilatoxinas. Se hace además referencia a la presencia de receptores para el complemento, ubicados en la membrana de diversas células del sistema inmunológico, responsables de muchas de las principales actividades del sistema, como la fagocitosis de microorganismos a través de la unión de receptores para C3b (principal opsonina) sobre la membrana de las células fagocitarias

El sistema del complemento sérico: parte 1, mecanismos de reacción y efectos biológicos / The serum complement system: part1, activation mechanisms and biological effects

A un siglo de su descubrimiento por Bordet, se trata de poner un poco de orden en los mecanismos de activación del complemento a través de su hasta ahora conocidas rutas de activación clásica o de C1 y la vía alterna o de la properdina. Se hace además referencia a otras vías de activación descritas más recientemente como la activación iniciada por la lectina de unión a la manosa (MBL). Se destaca también la actividad de los componentes inhibidores o controladores, que frenan la actividad del sistema, evitando la producción de daños por la formación y liberación de péptidos con potente acción biológica derivados del mismo, tal el caso de las anafilatoxinas. Se hace además referencia a la presencia de receptores para el complemento, ubicados en la membrana de diversas células del sistema inmunológico, responsables de muchas de las principales actividades del sistema, como la fagocitosis de microorganismos a través de la unión de receptores para C3b (principal opsonina) sobre la membrana de las células fagocitarias (AU)