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Lectin Pathway (lectin + pathway)
Selected AbstractsRole of the complement-lectin pathway in anaphylactoid reaction induced with lipopolysaccharide in miceEUROPEAN JOURNAL OF IMMUNOLOGY, Issue 10 2003wierzko Abstract We show that Proteus vulgaris,O25 (PO25) lipopolysaccharide (LPS) induced an anaphylactoid reaction not only in wild-type and in lipid,A non-responding mice but also in recombinase-activating gene-2-deficient (RAG-2,/,) and in mast cell-deficient (W/Wv) animals. Western blot analysis indicated that PO25 LPS bound to Ra-reactive factor (RaRF), the complex of mannan-binding lectins (MBL) and MBL-associated serine proteases. Binding of RaRF to PO25 LPS led to the activation of C4 component without participation of either C1 or Ig, via the lectin pathway. Relative concentration of RaRF and hemolytic activity in mouse serum decreased rapidly during the process of anaphylactoid reaction. A significant drop of MBL-A, but not MBL-C level was observed. Administrationwith antiserum to RaRF prevented animals from death as a consequence of the inhibition of interaction of RaRF with the carbohydrate target and complement activation. These results indicate that complement-lectin pathway activation is responsible for the anaphylactoid reaction induced with LPS in muramyldipeptide-primed mice. RaRF also activated fibrinogen in vitro suggesting the involvement of the coagulation system in the process investigated. [source] Complement and its implications in cardiac ischemia/reperfusion: strategies to inhibit complementFUNDAMENTAL & CLINICAL PHARMACOLOGY, Issue 5 2001Tiphaine Monsinjon Although reperfusion of the ischemic myocardium is an absolute necessity to salvage tissue from eventual death, it is also associated with pathologic changes that represent either an acceleration of processes initiated during ischemia or new pathophysiological changes that were initiated after reperfusion. This so-called ,reperfusion injury' is accompanied by a marked inflammatory reaction, which contributes to tissue injury. In addition to the well known role of oxygen free radicals and white blood cells, activation of the complement system probably represents one of the major contributors of the inflammatory reaction upon reperfusion. The complement may be activated through three different pathways: the classical, the alternative, and the lectin pathway. During reperfusion, complement may be activated by exposure to intracellular components such as mitochondrial membranes or intermediate filaments. Two elements of the activated complement contribute directly or indirectly to damages: anaphylatoxins (C3a and C5a) and the membrane attack complex (MAC). C5a, the most potent chemotactic anaphylatoxin, may attract neutrophils to the site of inflammation, leading to superoxide production, while MAC is deposited over endothelial cells and smooth vessel cells, leading to cell injury. Experimental evidence suggests that tissue salvage may be achieved by inhibition of the complement pathway. As the complement is composed of a cascade of proteins, it provides numerous sites for pharmacological interventions during acute myocardial infarction. Although various strategies aimed at modulating the complement system have been tested, the ideal approach probably consists of maintaining the activity of C3 (a central protein of the complement cascade) and inhibiting the later events implicated in ischemia/reperfusion and also in targeting inhibition in a tissue-specific manner. [source] Prognosis in pediatric hematologic malignancies is associated with serum concentration of mannose-binding lectin-associated serine protease-2 (MASP-2)PEDIATRIC BLOOD & CANCER, Issue 1 2009Aina Zehnder MD Abstract Background Mannose-binding lectin (MBL) and MBL-associated serine protease-2 (MASP-2) are key components of the lectin pathway of complement activation. Their serum concentrations show a wide interindividual variability. This study investigated whether the concentration of MBL and MASP-2 is associated with prognosis in pediatric patients with cancer. Methods In this retrospective multicenter study, MBL and MASP-2 were measured by commercially available ELISA in frozen remnants of serum taken at diagnosis. Associations of overall survival (OS) and event-free survival (EFS) with MBL and MASP-2 were assessed by multivariate Cox regression accounting for prognostically relevant clinical variables. Results In the 372 patients studied, median serum concentration of MBL was 2,808 µg/L (range, 2,10,060) and 391 µg/L (46,2,771) for MASP-2. The estimated 4-year EFS was 0.60 (OS, 0.78). In the entire, heterogeneous sample, MBL and MASP-2 were not significantly associated with OS or EFS. In patients with hematologic malignancies, however, higher MASP-2 was associated with better EFS in a significant and clinically relevant way (hazard ratio per tenfold increase (HR), 0.22; 95% CI, 0.09,0.54; P,=,0.001). This was due to patients with lymphoma (HR, 0.11; 95% CI, 0.03,0.47; P,=,0.003), but less for those with acute leukemia (HR, 0.35; 95% CI, 0.11,1.15; P,=,0.083). Conclusion In this study, higher MASP-2 was associated with better EFS in pediatric patients with hematologic malignancies, especially lymphoma. Whether MASP-2 is an independent prognostic factor affecting risk stratification and anticancer therapy needs to be assessed in prospective, disease-specific studies. Pediatr Blood Cancer 2009;53:53,57. © 2009 Wiley-Liss, Inc. [source] Anti,cyclic citrullinated peptide antibodies from rheumatoid arthritis patients activate complement via both the classical and alternative pathwaysARTHRITIS & RHEUMATISM, Issue 7 2009L. A. Trouw Objective It has been suggested that anti,citrullinated protein antibodies (ACPAs) play an important role in the pathogenesis of rheumatoid arthritis (RA). To exert their pathologic effects, ACPAs must recruit immune effector mechanisms such as activation of the complement system. Mouse models of RA have shown that, surprisingly, arthritogenic antibodies activate the alternative pathway of complement rather than the expected classical pathway. This study was undertaken to investigate whether human anti,cyclic citrullinated peptide (anti-CCP) antibodies activate the complement system in vitro and, if so, which pathways of complement activation are used. Methods We set up novel assays to analyze complement activation by anti-CCP antibodies, using cyclic citrullinated peptide,coated plates, specific buffers, and normal and complement-deficient sera as a source of complement. Results Anti-CCP antibodies activated complement in a dose-dependent manner via the classical pathway of complement, and, surprisingly, via the alternative pathway of complement. The lectin pathway was not activated by anti-CCP antibodies. Complement activation proceeded in vitro up to the formation of the membrane attack complex, indicating that all activation steps, including the release of C5a, took place. Conclusion Our findings indicate that anti-CCP antibodies activate the complement system in vitro via the classical and alternative pathways but not via the lectin pathway. These findings are relevant for the design of interventions aimed at inhibition of complement-mediated damage in RA. [source] Ficolin 2 (FCN2) functional polymorphisms and the risk of rheumatic fever and rheumatic heart diseaseCLINICAL & EXPERIMENTAL IMMUNOLOGY, Issue 3 2009I. J. Messias-Reason Summary Ficolins are pattern-recognition proteins involved in innate immunity, which upon binding to their specific pathogen-associated molecular patterns on the microbial surfaces trigger the immune response either by binding to collectin cellular receptors or by initiating the complement lectin pathway. In humans, three ficolin genes have been identified, which encode ficolin-1 (M-ficolin), ficolin-2 (L-ficolin) and ficolin-3 (H-ficolin or Hakata antigen). Ficolin-2 was shown to bind to lipoteichoic acid, a cell wall constituent in all Gram-positive bacteria such as Streptococcus pyogenes, which is the aetiological agent of rheumatic fever (RF) and its most severe sequelae, chronic rheumatic heart disease (CRHD). Here we investigated polymorphisms in the promoter region of the FCN2 gene (at positions ,986/,602 and +4) in 122 patients with RF and CRHD and in 210 healthy subjects from the same geographic region and socioeconomic background. The haplotype ,986/,602/,4 G/G/A, which is related to low levels of L-ficolin, was observed more frequently in the CRHD group when compared to the healthy subjects [99/162, 61·1% versus 211/420, 50·2%, odds ratio (OR) 1·6, confidence interval (CI) 95% 1·1,2·3, P = 0·021]. The haplotype ,986/,602/,4 A/G/A was observed more frequently in the healthy group when compared to the affected (RF plus CRHD) subjects (31/420, 7·4% versus 6/244, 2·5%, OR 3·2, CI 95% 0·13,0·77, P = 0·008). Based on those findings, one can conclude that polymorphisms associated with low levels of L-ficolin level may predispose an individual to recurrent and/or more severe streptococcal infection. [source] Design of a complement mannose-binding lectin pathway-specific activation system applicable at low serum dilutionsCLINICAL & EXPERIMENTAL IMMUNOLOGY, Issue 3 2006M. Harboe Summary Recently we showed that alternative pathway (AP) amplification was responsible for more than 80% of specific classical pathway-induced terminal pathway activation under physiological conditions. The present study aimed to design a system for specific lectin pathway (LP) activation applicable at low serum dilutions with a fully functional AP. Comparison between activation of normal human serum (NHS), a mannose-binding lectin (MBL) homozygous D/D -deficient serum, and sera deficient in C1q and C2, all diluted 1 : 2, was essential to document optimal conditions for LP specificity. Mannan on the solid phase of enzyme-linked immunosorbent assay (ELISA) plates was used for activation, showing 0·5 µg mannan/well to give optimal conditions because at this concentration a good signal was preserved for C4 and TCC deposition in NHS, whereas the C3 deposition observed in C2-deficient serum at higher mannan concentrations reached nadir at 0·5 µg/well, indicating a lack of direct AP activation under these conditions. Pooled NHS and C1q-deficient serum gave the same degree of C4 and terminal complement complex (TCC) deposition, whereas deposition of these products was not obtained with MBL-deficient serum. Reconstitution with purified MBL, however, restored the depositions. A blocking anti-MBL monoclonal antibody (mAb) completely abolished the complement deposition, in contrast to a non-inhibiting anti-MBL mAb. Activation of C2-deficient serum induced C4 deposition similar to NHS, but negligible deposition of C3 and TCC, confirming the lack of direct activation of AP. Thus, this assay is unique in being LP-specific at low serum dilution and thus particularly suitable to study LP activation mechanisms and the role of AP amplification under physiological conditions. [source] C4d deposition on peritubular capillary (PTC) in the protocol biopsy of ABO-incompatible kidney transplantation under the treatment with anti-CD20 antibody and without splenectomyCLINICAL TRANSPLANTATION, Issue 2007Naofumi Imai Abstract:, For the desensitization of A/B antigens, we had developed and reported a new potent immunosuppressive treatment, which is the pre-prescription of anti-CD20 monoclonal antibody with mycophenolate mofetil and low-dose steroid. Using this kind of desensitization therapy, splenectomy is not required at the kidney transplantation. Complement C4d deposition on peritubular capillary (PTC) in graft biopsy has been reported as a relatively reliable marker for humoral rejection. However, the C4d deposition was often observed in the graft biopsy of ABO-incompatible kidney transplantation even with no rejection findings. The aim of this study was to examine the effect of this treatment on C4d deposition on PTC. Baseline and protocol graft biopsies obtained from 12 recipients of ABO incompatible kidney transplants were evaluated by light and immunofluorescence microscopy. To elucidate the involvement of classical and/or lectin pathway of complement cascades in C4d deposition, we examined the deposition of the initial activating proteins on PTC, IgG and IgM in the classical pathway and mannose-binding lectin (MBL), H-ficolin, L-ficolin, MBL-associated serine protease (MASP)-1 and MASP-2 in the lectin pathway. Three out of nine available baseline biopsy specimens showed diffuse C4d and IgM deposition on PTC. In the protocol biopsy, nine of 12 specimens revealed diffuse C4d deposition on PTC. Five of them had positive deposition of IgM and H-ficolin on PTC, whereas the other initial proteins were not detected in all specimens. Apart from one case, the histological findings of the protocol biopsies were normal or borderline changes. Our study suggested that although the new treatment with anti-CD20 antibody treatment and without splenectomy was clinically effective, it did not perfectly inhibit C4d deposition on PTC. It also confirmed the dual activation of both classical and lectin pathways in the process of C4d deposition on PTC in ABO-incompatible transplantation. [source] The lectin-like domain of thrombomodulin interferes with complement activation and protects against arthritisJOURNAL OF THROMBOSIS AND HAEMOSTASIS, Issue 8 2006M. VAN DE WOUWER Summary.,Background: Thrombomodulin (TM) is predominantly a vascular endothelial cell plasma membrane glycoprotein that, via distinct structural domains, interacts with multiple ligands, thereby modulating coagulation, fibrinolysis, complement activation, inflammation and cell proliferation. We previously reported that by mediating signals that interfere with mitogen-activated protein kinase and nuclear factor ,B pathways, the amino-terminal C-type lectin-like domain of TM has direct anti-inflammatory properties. Methods: In the current study, we use murine models of acute inflammatory arthritis and biochemical approaches to assess the mechanism by which the lectin-like domain of TM modifies disease progression. Results: Mice lacking the lectin-like domain of TM (TMLeD/LeDmice) develop inflammatory arthritis that is more rapid in onset and more severe than that developed in their wildtype counterparts. In two models of arthritis, treatment of mice with recombinant soluble lectin-like domain of TM significantly suppresses clinical evidence of disease and diminishes monocyte/macrophage infiltration into the synovium, with weaker expression of the pro-inflammatory high mobility group box chromosomal protein 1. While thrombin-TM mediated activation of thrombin activatable fibrinolysis inhibitor inactivates complement factors C3a and C5a, we show that TM has a second independent mechanism to regulate complement: the lectin-like domain of TM directly interferes with complement activation via the classical and lectin pathways. Conclusions: These data extend previous insights into the mechanisms by which TM modulates innate immunity, and highlight its potential as a therapeutic target for inflammatory diseases. [source] The structure of C2b, a fragment of complement component C2 produced during C3 convertase formationACTA CRYSTALLOGRAPHICA SECTION D, Issue 3 2009Vengadesan Krishnan The second component of complement (C2) is a multi-domain serine protease that provides catalytic activity for the C3 and C5 convertases of the classical and lectin pathways of human complement. The formation of these convertases requires the Mg2+ -dependent binding of C2 to C4b and the subsequent cleavage of C2 by C1s or MASP2, respectively. The crystal structure of full-length C2 is not yet available, although the structure of its C-terminal catalytic segment C2a has been determined. The crystal structure of the N-terminal segment C2b of C2 determined to 1.8,Å resolution presented here reveals the arrangement of its three CCP domains. The domains are arranged differently compared with most other CCP-domain assemblies, but their arrangement is similar to that found in the Ba part of the full-length factor B structure. The crystal structures of C2a, C2b and full-length factor B are used to generate a model for C2 and a discussion of the domain association and possible interactions with C4b during formation of the C4b,C2 complex is presented. The results of this study also suggest that upon cleavage by C1s, C2a domains undergo conformational rotation while bound to C4b and the released C2b domains may remain folded together similar to as observed in the intact protein. [source] C4d deposition on peritubular capillary (PTC) in the protocol biopsy of ABO-incompatible kidney transplantation under the treatment with anti-CD20 antibody and without splenectomyCLINICAL TRANSPLANTATION, Issue 2007Naofumi Imai Abstract:, For the desensitization of A/B antigens, we had developed and reported a new potent immunosuppressive treatment, which is the pre-prescription of anti-CD20 monoclonal antibody with mycophenolate mofetil and low-dose steroid. Using this kind of desensitization therapy, splenectomy is not required at the kidney transplantation. Complement C4d deposition on peritubular capillary (PTC) in graft biopsy has been reported as a relatively reliable marker for humoral rejection. However, the C4d deposition was often observed in the graft biopsy of ABO-incompatible kidney transplantation even with no rejection findings. The aim of this study was to examine the effect of this treatment on C4d deposition on PTC. Baseline and protocol graft biopsies obtained from 12 recipients of ABO incompatible kidney transplants were evaluated by light and immunofluorescence microscopy. To elucidate the involvement of classical and/or lectin pathway of complement cascades in C4d deposition, we examined the deposition of the initial activating proteins on PTC, IgG and IgM in the classical pathway and mannose-binding lectin (MBL), H-ficolin, L-ficolin, MBL-associated serine protease (MASP)-1 and MASP-2 in the lectin pathway. Three out of nine available baseline biopsy specimens showed diffuse C4d and IgM deposition on PTC. In the protocol biopsy, nine of 12 specimens revealed diffuse C4d deposition on PTC. Five of them had positive deposition of IgM and H-ficolin on PTC, whereas the other initial proteins were not detected in all specimens. Apart from one case, the histological findings of the protocol biopsies were normal or borderline changes. Our study suggested that although the new treatment with anti-CD20 antibody treatment and without splenectomy was clinically effective, it did not perfectly inhibit C4d deposition on PTC. It also confirmed the dual activation of both classical and lectin pathways in the process of C4d deposition on PTC in ABO-incompatible transplantation. [source] | ||||||||||