Lectin Pathway Of Complement Activation Research Articles

Characterization of mannose‐binding lectin (MBL) variants by allele‐specific sequencing of MBL2 and determination of serum MBL protein levels

Mannose-binding lectin (MBL) is a major component of the lectin pathway of complement activation. High and low MBL levels have been associated with susceptibility and severity of a variety of infectious and autoimmune diseases. Several single-nucleotide polymorphisms (SNPs) in the promoter region and exon 1 of the MBL2 gene are responsible for variations in serum MBL levels. We developed a sequence-based typing method for allele-specific MBL2 genotyping and measured serum MBL protein levels in 24 German blood donors. We identified the common MBL2 haplotypes including five promoter polymorphisms in linkage with the Q allele and correlated serum MBL levels with the respective genotypes. The genotyping method presented here could provide a basis for confirmatory studies in larger cohorts.

Lectin pathway of complement activation and relation with clinical complications in critically ill children

Critically ill children are susceptible to nosocomial infections, which contribute to adverse outcomes. Deficiencies in the innate immunity lectin pathway of complement activation are implicated in a child's vulnerability to infections in conditions such as cancer, but the role during critical illness remains unclear. We hypothesized that low on-admission levels of the pathway proteins are, in part, genetically determined and associated with susceptibility to infectious complications and adverse outcomes. We studied protein levels of mannose-binding lectin (MBL), H-ficolin and M-ficolin, three MBL-associated-serine proteases (MASPs) and MBL-associated protein (MAp44), and relation with functional genetic polymorphisms, in 130 healthy children and upon intensive care unit (ICU) admission in 700 critically ill children of a randomized study on glycemic control. Levels of MASP-1, MASP-2, MASP-3, and MAp-44 were lower and the levels of M-ficolin were higher in ICU patients on admission than those in matched healthy controls. Only a low on-admission MASP-3 level was independently associated with risk of new ICU infections and prolonged ICU stay, after correcting for other risk factors. On-admission MASP-3 varied with age, illness severity, and genetic variation. Low on-admission MASP-3 levels in critically ill children were independently associated with subsequent acquisition of infection and prolonged ICU stay. The biological explanation needs further investigation.

Mannan binding lectin-associated serine protease 1 is induced by hepatitis C virus infection and activates human hepatic stellate cells

Mannan binding lectin (MBL)-associated serine protease type 1 (MASP-1) has a central role in the lectin pathway of complement activation and is required for the formation of C3 convertase. The activity of MASP-1 in the peripheral blood has been identified previously as a highly significant predictor of the severity of liver fibrosis in hepatitis C virus (HCV) infection, but not in liver disease of other aetiologies. In this study we tested the hypotheses that expression of MASP-1 may promote disease progression in HCV disease by direct activation of hepatic stellate cells (HSCs) and may additionally be up-regulated by HCV. In order to do so, we utilized a model for the maintenance of primary human HSC in the quiescent state by culture on basement membrane substrate prior to stimulation. In comparison to controls, recombinant MASP-1 stimulated quiescent human HSCs to differentiate to the activated state as assessed by both morphology and up-regulation of HSC activation markers α-smooth muscle actin and tissue inhibitor of metalloproteinase 1. Further, the expression of MASP-1 was up-regulated significantly by HCV infection in hepatocyte cell lines. These observations suggest a new role for MASP-1 and provide a possible mechanistic link between high levels of MASP-1 and the severity of disease in HCV infection. Taken together with previous clinical observations, our new findings suggest that the balance of MASP-1 activity may be proinflammatory and act to accelerate fibrosis progression in HCV liver disease.

Ficolin-2 Defends against Virulent Mycobacteria Tuberculosis Infection In Vivo, and Its Insufficiency Is Associated with Infection in Humans

Human ficolin-2 (ficolin-2/P35) is a lectin complement pathway activator that is present in normal human plasma and is associated with infectious diseases; however, little is known regarding the roles and mechanisms of ficolin-2 during Mycobacterium tuberculosis (Mtb) infection. Here, we describe our novel findings that the ficolin-2 serum levels of 107 pulmonary tuberculosis (TB) patients were much lower compared with 107 healthy controls. In vitro analysis showed that ficolin-2 bound to the virulent Mtb H37Rv strain much more strongly than to the non-virulent M. bovis BCG and M. smegmatis. Ficolin-2 bound to the surface glycolipid portion of H37Rv and blocked H37Rv infection in human lung A549 cells. Opsonophagocytosis was also promoted by ficolin-2. Importantly, we found that administration of exogenous ficolin-2 had a remarkable protective effect against virulent Mtb H37Rv infection in both C57BL/6J and BALB/c mice. Ficolin-A (a ficolin-2-like molecule in mouse) knockout mice exhibited increased susceptibility to H37Rv infection. We further demonstrated that ficolin-2 could defend against virulent Mtb H37Rv infection at least partially by activating JNK phosphorylation and stimulating the secretion of interferon (IFN)-γ, interleukin (IL)-17, IL-6, tumor necrosis factor (TNF)-α, and nitric oxide (NO) production by macrophages. Our data provide a new immunotherapeutic strategy against TB based on the innate immune molecule ficolin-2 and indicate that ficolin-2 insufficiency is associated with higher susceptibility to infection in humans.

Investigations on Collectin Liver 1

Collectins are pattern recognition molecules of the innate immune system showing binding to carbohydrate structures on microorganisms in a calcium-dependent manner. Recently, three novel collectins, collectin liver 1 (CL-L1), collectin kidney 1 (CL-K1 and CL-11), and collectin placenta 1 (CL-P1), were discovered. The roles of these three collectins remain largely unknown. Here, we present a time-resolved immunofluorometric assay for quantification of CL-L1. The concentration of CL-L1 in donor plasma (n = 210) was distributed log-normally with a median value of 3.0 μg/ml (range 1.5-5.5 μg/ml). We observed on average 30% higher concentrations of CL-L1 in plasma as compared with serum. Size analysis by gel-permeation chromatography showed CL-L1 in serum to elute as large 700-800-kDa complexes and smaller 200-300-kDa complexes. CL-L1 showed specific binding to mannose-TSK beads in a Ca(2+)-dependent manner. This binding could be inhibited by mannose and glucose, but not galactose, indicating that CL-L1 binds via its carbohydrate-recognition domain and has ligand specificity similar to that of mannan-binding lectin. Western blot analysis of CL-L1 showed the presence of several oligomeric forms in serum. Ontogeny studies showed CL-L1 to be present at birth at near adult levels. CL-L1 levels exhibit low variation in healthy adults over a 1-year period. During acute-phase responses, the CL-L1 levels display only minor variations. In serum, CL-L1 was found in complexes with mannan-binding lectin-associated serine proteases, suggesting a role in the lectin pathway of complement activation. The presented data establish a basis for future studies on the biological role of CL-L1.

Ficolin-3 mediated lectin complement pathway activation is related to pathology and outcome in subarachnoid haemorrhage patients

Ficolin-3 mediated lectin complement pathway activation is related to pathology and outcome in subarachnoid haemorrhage patients

C1q-targeted monoclonal antibody prevents complement-dependent cytotoxicity and neuropathology in in vitro and mouse models of neuromyelitis optica

Neuromyelitis optica (NMO) is an autoimmune disorder with inflammatory demyelinating lesions in the central nervous system, particularly in the spinal cord and optic nerve. NMO pathogenesis is thought to involve binding of anti-aquaporin-4 (AQP4) autoantibodies to astrocytes, which causes complement-dependent cytotoxicity (CDC) and downstream inflammation leading to oligodendrocyte and neuronal injury. Vasculocentric deposition of activated complement is a prominent feature of NMO pathology. Here, we show that a neutralizing monoclonal antibody against the C1q protein in the classical complement pathway prevents AQP4 autoantibody-dependent CDC in cell cultures and NMO lesions in ex vivo spinal cord slice cultures and in mice. A monoclonal antibody against human C1q with 11nM binding affinity prevented CDC caused by NMO patient serum in AQP4-transfected cells and primary astrocyte cultures, and prevented complement-dependent cell-mediated cytotoxicity (CDCC) produced by natural killer cells. The anti-C1q antibody prevented astrocyte damage and demyelination in mouse spinal cord slice cultures exposed to AQP4 autoantibody and human complement. In a mouse model of NMO produced by intracerebral injection of AQP4 autoantibody and human complement, the inflammatory demyelinating lesions were greatly reduced by intracerebral administration of the anti-C1q antibody. These results provide proof-of-concept for C1q-targeted monoclonal antibody therapy in NMO. Targeting of C1q inhibits the classical complement pathway directly and causes secondary inhibition of CDCC and the alternative complement pathway. As C1q-targeted therapy leaves the lectin complement activation pathway largely intact, its side-effect profile is predicted to differ from that of therapies targeting downstream complement proteins.

Deposition of the lectin pathway of complement in renal biopsies of lupus nephritis patients

Lupus nephritis (LN) is one of the most serious manifestations of SLE occurring in 66-90% of these patients. The complement system is part of the innate immunity and modulator of inflammation and the adaptative immune response. Mannan-binding lectin (MBL) and Ficolin-2 (FCN-2) are important members of the lectin pathway of complement activation. Despite the significant participation of complement in the pathogenesis of the LN, there are few reports demonstrating "in situ" deposition of complement components in renal biopsy specimens in this disorder. The present study investigated the deposition of complement components in kidney specimens of LN patients. Renal biopsies of 11 patients with SLE and LN were evaluated for immunofluorescence staining for IgG, IgA, IgM, C3, and C1q. Additionally, MBL, FCN-2 and C5b-9 were researched using monoclonal antibodies. All the biopsies were positive for IgG, C3, and C1q, eight were positive IgM and five had IgA deposition in glomerular tissue. The terminal complex of complement C5b9 was positive in all cases, MBL in nine (82%) cases; seven (63.6%) of them presenting concomitantly FCN-2 deposition. Patients presenting MBL deposition had higher mean of urinary proteins (9.0 g/day) than patients with negative MBL deposition (mean of 2.3g/day). In this study, we demonstrated in situ the participation of complement in the renal injury, including MBL and FCN-2 of the lectin pathway; also the strong role of C5b-9 in the pathogenesis of LN.

Role of Ficolin-A and Lectin Complement Pathway in the Innate Defense against Pathogenic Aspergillus Species

Aspergillus species are saprophytic molds causing life-threatening invasive fungal infections in the immunocompromised host. Innate immune recognition, in particular, the mechanisms of opsonization and complement activation, has been reported to be an integral part of the defense against fungi. We have shown that the complement component ficolin-A significantly binds to Aspergillus conidia and hyphae in a concentration-dependent manner and was inhibited by N-acetylglucosamine and N-acetylgalactosamine. Calcium-independent binding to Aspergillus fumigatus and A. terreus was observed, but binding to A. flavus and A. niger was calcium dependent. Ficolin-A binding to conidia was increased under low-pH conditions, and opsonization led to enhanced binding of conidia to A549 airway epithelial cells. In investigations of the lectin pathway of complement activation, ficolin-A-opsonized conidia did not lead to lectin pathway-specific C4 deposition. In contrast, the collectin mannose binding lectin C (MBL-C) but not MBL-A led to efficient lectin pathway activation on A. fumigatus in the absence of ficolin-A. In addition, ficolin-A opsonization led to a modulation of the proinflammatory cytokine interleukin-8. We conclude that ficolin-A may play an important role in the innate defense against Aspergillus by opsonizing conidia, immobilizing this fungus through enhanced adherence to epithelial cells and modulation of inflammation. However, it appears that other immune pattern recognition molecules, i.e., those of the collectin MBL-C, are involved in the Aspergillus-lectin complement pathway activation rather than ficolin-A.

Quantitative Characterization of the Activation Steps of Mannan-binding Lectin (MBL)-associated Serine Proteases (MASPs) Points to the Central Role of MASP-1 in the Initiation of the Complement Lectin Pathway

Mannan-binding lectin (MBL)-associated serine proteases, MASP-1 and MASP-2, have been thought to autoactivate when MBL/ficolin·MASP complexes bind to pathogens triggering the complement lectin pathway. Autoactivation of MASPs occurs in two steps: 1) zymogen autoactivation, when one proenzyme cleaves another proenzyme molecule of the same protease, and 2) autocatalytic activation, when the activated protease cleaves its own zymogen. Using recombinant catalytic fragments, we demonstrated that a stable proenzyme MASP-1 variant (R448Q) cleaved the inactive, catalytic site Ser-to-Ala variant (S646A). The autoactivation steps of MASP-1 were separately quantified using these mutants and the wild type enzyme. Analogous mutants were made for MASP-2, and rate constants of the autoactivation steps as well as the possible cross-activation steps between MASP-1 and MASP-2 were determined. Based on the rate constants, a kinetic model of lectin pathway activation was outlined. The zymogen autoactivation rate of MASP-1 is ∼3000-fold higher, and the autocatalytic activation of MASP-1 is about 140-fold faster than those of MASP-2. Moreover, both activated and proenzyme MASP-1 can effectively cleave proenzyme MASP-2. MASP-3, which does not autoactivate, is also cleaved by MASP-1 quite efficiently. The structure of the catalytic region of proenzyme MASP-1 R448Q was solved at 2.5 Å. Proenzyme MASP-1 R448Q readily cleaves synthetic substrates, and it is inhibited by a specific canonical inhibitor developed against active MASP-1, indicating that zymogen MASP-1 fluctuates between an inactive and an active-like conformation. The determined structure provides a feasible explanation for this phenomenon. In summary, autoactivation of MASP-1 is crucial for the activation of MBL/ficolin·MASP complexes, and in the proenzymic phase zymogen MASP-1 controls the process.

The control of the complement lectin pathway activation revisited: Both C1-inhibitor and antithrombin are likely physiological inhibitors, while α2-macroglobulin is not

The lectin pathway of complement is an important effector arm of innate immunity. It forms a first line of defense against invading pathogens and dangerously altered self structures. Pattern recognition molecules (mannose-binding lectin (MBL), ficolins) bind to the dangerous particles, which is followed by activation of MBL-associated serine proteases, MASP-1 and MASP-2, resulting in the initiation of the complement cascade. The activation of the lectin pathway is strictly controlled by natural inhibitors, since uncontrolled activation can lead to serious self-tissue damage. Recently we have shown that inhibition of either MASP-1 or MASP-2 by in vitro evolved specific inhibitors completely blocks the lectin pathway in human serum. In this study, we examined the inhibitory action of C1-inhibitor (C1-inh), antithrombin (AT) and α2-macroglobulin (α2M) on MASP-1 and MASP-2, and studied the inhibition of the lectin pathway in normal human serum in the presence and absence of heparin using C3 and C4 deposition assays. We measured the association rate constants for the serpin/protease reactions. We found that in the presence of heparin both C1-inh and AT are equally efficient inhibitors of the lectin pathway. Although α2M formed complex with MASP-1 in fluid phase, it could not abolish lectin pathway activation on activator surfaces.

IgM‐dependent activation of the lectin pathway of complement in xenotransplantation

Background: The classical pathway is the dominant initiator of complement activation in xenotransplantation. By amplification of C3b generation, the alternative pathway is also critical. However, little attention has been paid up to date to the involvement of the lectin pathway in xenograft rejection. Natural IgM, containing anti‐Gal, is a major initiator of classical pathway complement activation, but recently it has been shown that during ischemia/reperfusion injury, IgM also induces lectin pathway activation. Thus, the present study was focused on lectin pathway as well as interaction of IgM and MBL in a pig‐to‐human in vitro xenotransplantation model.Methods: Cell ELISA using porcine aortic endothelial cells (PAEC) and normal human serum (NHS) was used to assess activation of the different complement pathways. To confirm activation of the lectin pathway and to analyze the role of natural IgM in it's activation, co‐localized deposition of MBL/MASP2 with C3b/c, C4b/c & C6 and IgM with MBL & MASP2 was investigated by immunofluorescence (IF)/confocal microscopy on PAEC. Influence of IgM presence on MBL binding to PAEC was tested using IgM depleted/repleted and anti‐Gal immunoabsorbed NHS. Finally, tissue samples from ex vivo xenoperfusion of pig limbs with whole human blood were tested for IgM mediated lectin pathway activation by IF staining.Results: Activation of all the three pathways of complement system was observed in vitro as indicated by IgM, C1q, MBL and Factor Bb binding on PAEC. MBL deposition was co‐localized with MASP2, C3b/c, C4b/c and C6, suggesting a predominant role of the lectin pathway in xenograft rejection. IgM co‐localization with MBL and MASP2 as well as dose‐dependently increased deposition of MBL on PAEC in the presence of human polyclonal IgM, further supports the idea that upon deposition of IgM a binding site for MBL is exposed. In addition, co‐localized deposition of MBL with IgM, C4b/c and C6 was also observed on ex vivo xenoperfusion samples.Conclusion: The lectin pathway of complement activation was shown to be involved in xenotransplantation. Co‐localization of MBL / MASP2 with IgM and complement proteins indicate that lectin pathway activation in xenotransplantation is dependent on antigen recognition by naturalIgM. These findings suggest that, similar to ischemia/reperfusion injury, the lectin pathway has a functional role in endothelial damage in xenotransplantation.

Effect of Transgenic hCD46 Expression During Ex Vivo Xenoperfusion of hCD46/HLA-E Double Transgenic Pig Limbs with Human Blood

Background: To overcome rejection of pig-to-human xenografts, a new founder line with overexpression of human CD46 and HLA-E was analyzed in ex vivo perfusion experiments with respect to complement activation and cytokine responses. Methods: Six forelimbs (2 wild type and 4 hCD46/HLA-E transgenic pigs) were ex vivo perfused with whole, heparin-anticoagulated human blood. Blood samples were analyzed for production of porcine and/or human (p/h) cytokines and complement activation. Total complement activity was assessed by CH50 assay. Tissue samples were stained for deposition of human IgM, MBL, C3b/c, C4b/c, C6 and co-localization of MBL with IgM and C4b/c to determine the role of the lectin pathway of complement activation in xenotransplantation. Results: No hyperacute rejection was observed in this model and extremity perfusions lasted for up to 18 h, irrespective of the presence of the transgenes. Serum levels of p/h cytokines IL1b, IL-6, IL-8, IL-10, as well as sC5b-9 and sC4d were significantly lower in blood perfused through transgenic as compared to wild type limbs. CH50 results revealed early (1h) decrease of complement activity in all limb perfusions. Deposition of hIgM, MBL, C3b/c, C4b/c, and C6 were observed in tissue of wild type limbs, but no C6 deposition was found in transgenic limbs. Co-localization of MBL with IgM and C4b/c was also observed. Conclusion: The terminal pathway of complement activation was down-regulated by transgenic expression of CD46 and was associated with decreased cytokine production. In addition, deposition of MBL and it's co-localization with IgM and C4b/c suggested a role of antibodydependent activation of the lectin pathway of complement activation in xenotransplantation. Overall, this ex vivo perfusion system represents a powerful tool to study the basic mechanisms occurring in the setting of vascularized xenotransplantation and to evaluate the protection from early rejection mechanisms in tissues originating from transgenic pigs.

Trypanosoma cruzi carrying a monoallelic deletion of the calreticulin (TcCRT) gene are susceptible to complement mediated killing and defective in their metacyclogenesis

Trypanosoma cruzi calreticulin (TcCRT) can hijack complement C1, mannan-binding lectin and ficolins from serum thus inhibiting the classical and lectin complement pathway activation respectively. To understand the in vivo biological functions of TcCRT in T. cruzi we generated a clonal cell line lacking one TcCRT allele (TcCRT+/−) and another clone overexpressing it (TcCRT+). Both clones were derived from the TCC T. cruzi strain. As expected, TcCRT+/− epimastigotes showed impairment on TcCRT synthesis, whereas TcCRT+ ones showed increased protein levels. In correlation to this, monoallelic mutant parasites were significantly susceptible to killing by the complement machinery. On the contrary, TcCRT+ parasites showed higher levels of resistance to killing mediate by the classical and lectin but not the alternative pathway. The involvement of surface TcCRT in depleting C1 was demonstrated through restoration of serum killing activity by addition of exogenous C1. In axenic cultures, a reduced propagation rate of TcCRT+/− parasites was observed. Moreover, TcCRT+/− parasites presented a reduced rate of differentiation in in vitro assays. As shown by down- or upregulation of TcCRT expression this gene seems to play a major role in providing T. cruzi with the ability to resist complement system.

Crystal Structure and Functional Characterization of the Complement Regulator Mannose-binding Lectin (MBL)/Ficolin-associated Protein-1 (MAP-1)

The human lectin complement pathway activation molecules comprise mannose-binding lectin (MBL) and ficolin-1, -2, and -3 in complex with associated serine proteases MASP-1, -2, and -3 and the non-enzymatic small MBL associated protein or sMAP. Recently, a novel plasma protein named MBL/ficolin-associated protein-1 (MAP-1) was identified in humans. This protein is the result of a differential splicing of the MASP1 gene and includes the major part of the heavy chain but lacks the serine protease domain. We investigated the direct interactions of MAP-1 and MASP-3 with ficolin-3 and MBL using surface plasmon resonance and found affinities around 5 nm and 2.5 nm, respectively. We studied structural aspects of MAP-1 and could show by multi-angle laser light scattering that MAP-1 forms a calcium-dependent homodimer in solution. We were able to determine the crystal structure of MAP-1, which also contains a head-to-tail dimer ∼146 Å long. This structure of MAP-1 also enables modeling and assembly of the MASP-1 molecule in its entirety. Finally we found that MAP-1 competes with all three MASPs for ligand binding and is able to mediate a strong dose-dependent inhibitory effect on the lectin pathway activation, as measured by levels of C3 and C9.

The Lectin Pathway of Complement Activation Is a Critical Component of the Innate Immune Response to Pneumococcal Infection

The complement system plays a key role in host defense against pneumococcal infection. Three different pathways, the classical, alternative and lectin pathways, mediate complement activation. While there is limited information available on the roles of the classical and the alternative activation pathways of complement in fighting streptococcal infection, little is known about the role of the lectin pathway, mainly due to the lack of appropriate experimental models of lectin pathway deficiency. We have recently established a mouse strain deficient of the lectin pathway effector enzyme mannan-binding lectin associated serine protease-2 (MASP-2) and shown that this mouse strain is unable to form the lectin pathway specific C3 and C5 convertases. Here we report that MASP-2 deficient mice (which can still activate complement via the classical pathway and the alternative pathway) are highly susceptible to pneumococcal infection and fail to opsonize Streptococcus pneumoniae in the none-immune host. This defect in complement opsonisation severely compromises pathogen clearance in the lectin pathway deficient host. Using sera from mice and humans with defined complement deficiencies, we demonstrate that mouse ficolin A, human L-ficolin, and collectin 11 in both species, but not mannan-binding lectin (MBL), are the pattern recognition molecules that drive lectin pathway activation on the surface of S. pneumoniae. We further show that pneumococcal opsonisation via the lectin pathway can proceed in the absence of C4. This study corroborates the essential function of MASP-2 in the lectin pathway and highlights the importance of MBL-independent lectin pathway activation in the host defense against pneumococci.

Revised mechanism of complement lectin-pathway activation revealing the role of serine protease MASP-1 as the exclusive activator of MASP-2

The lectin pathway of complement activation is an important component of the innate immune defense. The initiation complexes of the lectin pathway consist of a recognition molecule and associated serine proteases. Until now the autoactivating mannose-binding lectin-associated serine protease (MASP)-2 has been considered the autonomous initiator of the proteolytic cascade. The role of the much more abundant MASP-1 protease was controversial. Using unique, monospecific inhibitors against MASP-1 and MASP-2, we corrected the mechanism of lectin-pathway activation. In normal human serum, MASP-2 activation strictly depends on MASP-1. MASP-1 activates MASP-2 and, moreover, inhibition of MASP-1 prevents autoactivation of MASP-2. Furthermore we demonstrated that MASP-1 produces 60% of C2a responsible for C3 convertase formation.

Good agreement between capillary and venous sampling for lectin pathway proteins

BackgroundThe lectin pathway of complement activation, in particular mannose-binding lectin (MBL), has been extensively investigated over recent years. So far, studies were exclusively based on venous samples. The aim of this study was to investigate whether measurements of lectin pathway proteins obtained by capillary sampling are in agreement with venous samples. MethodsProspective study including 31 infants that were admitted with suspected early-onset sepsis. Lectin pathway proteins were measured in simultaneously obtained capillary and venous samples. Bland–Altman plots of logarithmized results were constructed, and the mean capillary to venous ratios (ratiocap/ven) were calculated with their 95% confidence intervals (CI). ResultsThe agreement between capillary and venous sampling was very high for MBL (meanratiocap/ven, 1.01; 95% CI, 0.85–1.19). Similarly, high agreement was observed for H-ficolin (meanratiocap/ven, 1.02; 95% CI, 0.72–1.44), MASP-2 (1.04; 0.59–1.84), MASP-3 (0.96; 0.71–1.28), and MAp44 (1.01; 0.82–1.25), while the agreement was moderate for M-ficolin (meanratiocap/ven, 0.78; 95% CI, 0.27–2.28). ConclusionsThe results of this study show an excellent agreement between capillary and venous samples for most lectin pathway proteins. Except for M-ficolin, small volume capillary samples can thus be used when assessing lectin pathway proteins in neonates and young children.

The immunology of acute stroke

Recent clinical and experimental studies have highlighted a complex role for the immune system in the pathophysiological changes that occur after acute stroke. Sensors of the innate immune system such as Toll-like receptors, or effectors such as the lectin pathway of complement activation and innate immune cells, are activated by brain ischaemia and tissue damage, leading to amplification of the inflammatory cascade. Activation of the adaptive arm of the immune system, mediated by lymphocyte populations including T and B cells, regulatory T cells, and γδT cells, in response to stroke can lead to deleterious antigen-specific autoreactive responses but can also have cytoprotective effects. Increased incidence of infections is observed after acute stroke, and might result from activation of long-distance feedback loops between the CNS and peripheral immune organs, which are thought to play a part in stroke-induced immunodepression. Ongoing clinical trials are investigating whether the preventive use of antibiotics improves functional outcome after stroke. This Review discusses the multifaceted role of the immune system in the pathophysiology of acute stroke.

Circulating ficolin-2 and ficolin-3 in normal pregnancy and pre-eclampsia

Ficolins are soluble molecules of the innate immune system that recognize carbohydrate molecules on microbial pathogens, apoptotic and necrotic cells. They act through two distinct routes: initiating the lectin pathway of complement activation and mediating a primitive opsonophagocytosis. In this study, we measured plasma levels of ficolin-2 and ficolin-3 in 60 pre-eclamptic patients, 60 healthy pregnant women and 59 healthy non-pregnant women by enzyme-linked immunosorbent assay (ELISA). Circulating levels of complement activation products (C4d, C3a, SC5b9), angiogenic factors (soluble fms-like tyrosine kinase-1, placental growth factor) and markers of endothelial activation (von Willebrand factor antigen), endothelial injury (fibronectin) and trophoblast debris (cell-free fetal DNA) were also determined. Plasma levels of ficolin-2 were significantly lower in healthy pregnant than in healthy non-pregnant women, while ficolin-3 levels did not differ significantly between the two groups. Furthermore, pre-eclamptic patients had significantly lower ficolin-2 and ficolin-3 concentrations than healthy non-pregnant and pregnant women. In the pre-eclamptic group, plasma ficolin-2 levels showed a significant positive correlation with serum placental growth factor (PlGF) concentrations and significant inverse correlations with serum levels of soluble fms-like tyrosine kinase-1 (sFlt-1), blood urea nitrogen and creatinine, serum lactate dehydrogenase activities, as well as with plasma VWF:antigen, fibronectin and cell-free fetal DNA concentrations. In conclusion, circulating levels of ficolin-2 are decreased in the third trimester of normal pregnancy. There is a further decrease in plasma ficolin-2 concentrations in pre-eclampsia, which might contribute to the development of the maternal syndrome of the disease through impaired removal of the trophoblast-derived material released into the maternal circulation by the hypoxic and oxidatively stressed pre-eclamptic placenta.