Summary
Mannose‐binding lectin (MBL), collectin‐10, collectin‐11, and the ficolins (ficolin‐1, ficolin‐2, and ficolin‐3) are soluble pattern recognition molecules in the lectin complement pathway. ...These proteins act as mediators of host defense and participate in maintenance of tissue homeostasis. They bind to conserved pathogen‐specific structures and altered self‐antigens and form complexes with the pentraxins to modulate innate immune functions. All molecules exhibit distinct expression in different tissue compartments, but all are found to a varying degree in the circulation. A common feature of these molecules is their ability to interact with a set of serine proteases named MASPs (MASP‐1, MASP‐2, and MASP‐3). MASP‐1 and ‐2 trigger the activation of the lectin pathway and MASP‐3 may be involved in the activation of the alternative pathway of complement. Furthermore, MASPs mediate processes related to coagulation, bradykinin release, and endothelial and platelet activation. Variant alleles affecting expression and structure of the proteins have been associated with a variety of infectious and non‐infectious diseases, most commonly as disease modifiers. Notably, the severe 3MC (Malpuech, Michels, Mingarelli, and Carnevale) embryonic development syndrome originates from rare mutations affecting either collectin‐11 or MASP‐3, indicating a broader functionality of the complement system than previously anticipated. This review summarizes the characteristics of the molecules in the lectin pathway.
Essentials
The lectin pathway's MASP‐1/2 activates coagulation factors but the trigger of the activation is unknown.
MASP‐1/2 activation was assessed by quantifying complexes between MASPs and ...antithrombin/C1‐inhibitor.
Activated platelets and fibrin were demonstrated to activate MASP‐1 and MASP‐2 both in vitro and in vivo.
These findings may represent a crossroad between the complement and the coagulation systems.
Summary
Background
The activated forms of the complement lectin pathway (LP) proteases MASP‐1 and MASP‐2 are able to cleave the coagulation factors prothrombin, fibrinogen, factor XIII and thrombin‐activatable fibrinolysis inhibitor in vitro. In vivo studies also show that MASP‐1 is involved in thrombogenesis.
Objectives
To clarify the not yet identified mechanisms involved in triggering activation of the LP during thrombotic reactions.
Methods
Novel sandwich‐ELISAs for detection of complexes between MASP‐1 or MASP‐2 and the serpins C1 inhibitor (C1‐INH) or antithrombin (AT), were used to specifically detect and quantify the activated forms of MASP‐1 and MASP‐2.
Results
Activated platelets were shown by flow cytometry to bind Ficolin‐1, ‐2 and ‐3 but not MBL, which was associated with activation of MASP‐1 and MASP‐2. We also demonstrated that fibrin and the plasmin‐generated fibrin fragment DD in plasma, bind and activate MASP‐1 and MASP‐2. As demonstrated by the ELISA and SDS‐PAGE/Western blotting, the fibrin‐associated activation was reflected in a specific inactivation by AT during clotting without the assistance of heparin. In all other cases the MASPs were, as previously reported, inactivated by C1‐INH. In systemic lupus erythematosus patients with thrombotic disease and in polytrauma patients, the levels of activated MASP‐1 and MASP‐2 in complex with both AT and C1‐INH were associated with markers of thrombotic disease and contact/coagulation system activation.
Conclusions
MASP‐1 and MASP‐2 are activated during blood clotting. This activation is triggered by activated platelets and by the generation of fibrin during thrombotic reactions in vitro and in vivo, and may represent a novel activation/amplification mechanism in thromboinflammation.
It is now well established that tumours undergo changes in cellular metabolism
. As this can reveal tumour cell vulnerabilities and because many tumours exhibit enhanced glucose uptake
, we have been ...interested in how tumour cells respond to different forms of sugar. Here we report that the monosaccharide mannose causes growth retardation in several tumour types in vitro, and enhances cell death in response to major forms of chemotherapy. We then show that these effects also occur in vivo in mice following the oral administration of mannose, without significantly affecting the weight and health of the animals. Mechanistically, mannose is taken up by the same transporter(s) as glucose
but accumulates as mannose-6-phosphate in cells, and this impairs the further metabolism of glucose in glycolysis, the tricarboxylic acid cycle, the pentose phosphate pathway and glycan synthesis. As a result, the administration of mannose in combination with conventional chemotherapy affects levels of anti-apoptotic proteins of the Bcl-2 family, leading to sensitization to cell death. Finally we show that susceptibility to mannose is dependent on the levels of phosphomannose isomerase (PMI). Cells with low levels of PMI are sensitive to mannose, whereas cells with high levels are resistant, but can be made sensitive by RNA-interference-mediated depletion of the enzyme. In addition, we use tissue microarrays to show that PMI levels also vary greatly between different patients and different tumour types, indicating that PMI levels could be used as a biomarker to direct the successful administration of mannose. We consider that the administration of mannose could be a simple, safe and selective therapy in the treatment of cancer, and could be applicable to multiple tumour types.
Abstract
Mannose-capped lipoarabinomannan (ManLAM), present in all members of the Mycobacterium tuberculosis complex and in other pathogenic Mycobacterium spp, is a high molecular mass amphipathic ...lipoglycan with a defined critical role in mycobacterial survival during infection. In particular, ManLAM is well-characterized for its importance in providing M. tuberculosis a safe portal of entry to phagocytes, regulating the intracellular trafficking network, as well as immune responses of infected host cells. These ManLAM immunological characteristics are thought to be linked to the subtle but unique and well-defined structural characteristics of this molecule, including but not limited to the degree of acylation, the length of the D-mannan and D-arabinan cores, the length of the mannose caps, as well as the presence of other acidic constituents such as succinates, lactates and/or malates, and also the presence of 5-methylthioxylosyl. The impact of all these structural features on ManLAM spatial conformation and biological functions during M. tuberculosis infection is still uncertain. In this review, we dissect the relationship between ManLAM structure and biological function addressing how this relationship determines M. tuberculosis interactions with host cells, and how it aids this exceptional pathogen during the course of infection.
Mycobacterium tuberculosis mannose-capped lipoarabinomannan: relationship between structure and biological function.
The humoral arm of innate immunity includes diverse molecules with antibody-like functions, some of which serve as disease severity biomarkers in coronavirus disease 2019 (COVID-19). The present ...study was designed to conduct a systematic investigation of the interaction of human humoral fluid-phase pattern recognition molecules (PRMs) with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Of 12 PRMs tested, the long pentraxin 3 (PTX3) and mannose-binding lectin (MBL) bound the viral nucleocapsid and spike proteins, respectively. MBL bound trimeric spike protein, including that of variants of concern (VoC), in a glycan-dependent manner and inhibited SARS-CoV-2 in three in vitro models. Moreover, after binding to spike protein, MBL activated the lectin pathway of complement activation. Based on retention of glycosylation sites and modeling, MBL was predicted to recognize the Omicron VoC. Genetic polymorphisms at the MBL2 locus were associated with disease severity. These results suggest that selected humoral fluid-phase PRMs can play an important role in resistance to, and pathogenesis of, COVID-19, a finding with translational implications.
The complement system is a first-line innate host immune defence against invading pathogens. It is activated via three pathways, termed Classical, Lectin and Alternative, which are mediated by ...antibodies, carbohydrate arrays or microbial liposaccharides, respectively. The three complement pathways converge in the formation of C3-convertase followed by the assembly of a lethal pore-like structure, the membrane attack complex (MAC), on the pathogen surface. We found that the infectious stage of the helminth parasite Fasciola hepatica, the newly excysted juvenile (NEJ), is resistant to the damaging effects of complement. Despite being coated with mannosylated proteins, the main initiator of the Lectin pathway, the mannose binding lectin (MBL), does not bind to the surface of live NEJ. In addition, we found that recombinantly expressed serine protease inhibitors secreted by NEJ (rFhSrp1 and rFhSrp2) selectively prevent activation of the complement via the Lectin pathway. Our experiments demonstrate that rFhSrp1 and rFhSrp2 inhibit native and recombinant MBL-associated serine proteases (MASPs), impairing the primary step that mediates C3b and C4b deposition on the NEJ surface. Indeed, immunofluorescence studies show that MBL, C3b, C4b or MAC are not deposited on the surface of NEJ incubated in normal human serum. Taken together, our findings uncover new means by which a helminth parasite prevents the activation of the Lectin complement pathway to become refractory to killing via this host response, in spite of presenting an assortment of glycans on their surface.
Background Community-acquired pneumonia (CAP) is the leading cause of death from infection in developed countries. Mannose-binding lectin (MBL) and MBL-associated serine protease 2 (MASP-2) ...deficiencies are common primary immunodeficiencies the clinical penetrance of which remains controversial. MBL is a serum lectin that mediates phagocytosis and activates the lectin pathway of complement involving MASP-2. Objective We sought to evaluate the significance of MBL deficiency ( O/O genotypes) and insufficiency ( O/O plus XA/O genotypes), as well as MASP-2 deficiency ( D105G mutation), in the susceptibility to and severity and outcome of CAP in adults. Methods MBL and MASP-2 serum levels, as well as lectin pathway activity with regard to MBL2 and MASP2 genotypes, were measured in healthy control subjects. For susceptibility, 848 patients with CAP, 1447 healthy control subjects, and a control group of 519 patients without relevant infectious diseases were studied in a case-control study. Severity and outcome were evaluated in a prospective study of the 848 patients. Results We found similar frequencies of MBL2 and MASP2 alleles and genotypes among patients and control subjects. However, in a multivariate analysis MBL insufficiency was associated with the development of the most severe forms of sepsis ( P = .007), acute respiratory failure ( P = .009), multiorgan dysfunction syndrome ( P = .036), intensive care unit admission ( P = .020), and death ( P = .003). Conclusion Our large study suggests that MBL plays a redundant role in human defenses against primary infection, at least in adults with CAP, and provides, for the first time, evidence that MBL insufficiency predisposes to higher severity and fatal outcome in patients with CAP, irrespective of the causal microorganisms.
•Narsoplimab down-modulates SARS-CoV-2-induced activation of the lectin pathway and endothelial cell damage.•Narsoplimab can reduce the thrombotic risk of Covid-19 patients.•All patients treated with ...narsoplimab improved and survived without any drug-related adverse events.
In COVID-19, acute respiratory distress syndrome (ARDS) and thrombotic events are frequent, life-threatening complications. Autopsies commonly show arterial thrombosis and severe endothelial damage. Endothelial damage, which can play an early and central pathogenic role in ARDS and thrombosis, activates the lectin pathway of complement. Mannan-binding lectin-associated serine protease-2 (MASP-2), the lectin pathway’s effector enzyme, binds the nucleocapsid protein of severe acute respiratory syndrome-associated coronavirus-2 (SARS-CoV-2), resulting in complement activation and lung injury. Narsoplimab, a fully human immunoglobulin gamma 4 (IgG4) monoclonal antibody against MASP-2, inhibits lectin pathway activation and has anticoagulant effects. In this study, the first time a lectin-pathway inhibitor was used to treat COVID-19, six COVID-19 patients with ARDS requiring continuous positive airway pressure (CPAP) or intubation received narsoplimab under compassionate use. At baseline and during treatment, circulating endothelial cell (CEC) counts and serum levels of interleukin-6 (IL-6), interleukin-8 (IL-8), C-reactive protein (CRP) and lactate dehydrogenase (LDH) were assessed. Narsoplimab treatment was associated with rapid and sustained reduction of CEC and concurrent reduction of serum IL-6, IL-8, CRP and LDH. Narsoplimab was well tolerated; no adverse drug reactions were reported. Two control groups were used for retrospective comparison, both showing significantly higher mortality than the narsoplimab-treated group. All narsoplimab-treated patients recovered and survived. Narsoplimab may be an effective treatment for COVID-19 by reducing COVID-19-related endothelial cell damage and the resultant inflammation and thrombotic risk.
We investigated clinical associations of ficolins and mannose-binding lectin (MBL) in 157 patients suffering from acute myeloid leukaemia (AML). Concentrations of ficolin-1, ficolin-2, ficolin-3 and ...MBL (before chemotherapy) in serum were determined as were selected polymorphisms of the corresponding genes (FCN1, FCN2, FCN3 and MBL2). The control group (C) consisted of 267 healthy unrelated individuals. Median level of ficolin-1 in patients was lower (p < 0.000001) while median levels of ficolin-2, ficolin-3 and MBL were higher (p < 0.000001, p < 0.000001 and p = 0.0016, respectively) compared with controls. These findings were generally associated with AML itself, however the highest MBL levels predicted higher risk of severe hospital infections (accompanied with bacteremia and/or fungaemia) (p = 0.012) while the lowest ficolin-1 concentrations tended to be associated with prolonged (> 7 days) fever (p = 0.026). Genotyping indicated an association of G/G homozygosity (corresponding to FCN1 gene - 542 G > A polymorphism) with malignancy p = 0.004, OR = 2.95, 95% CI (1.41-6.16). Based on ROC analysis, ficolin-1, -2 and -3 may be considered candidate supplementary biomarkers of AML. Their high potential to differentiate between patients from non-malignant controls but also from persons suffering from other haematological cancers (multiple myeloma and lymphoma) was demonstrated.
MBL-deficiency is a commonly occurring deficiency of the innate immune system, affecting a substantial part of the population and has been extensively studied. MBL appears to function as a disease ...modifier. The role of MBL in different conditions is context-dependent. Many clinical studies show conflicting results, which can be partially explained by different definitions of MBL-deficiency, including phenotype- and genotype-based approaches. In this review we give an overview of literature of MBL, its role in different pathologies, diseases and patient populations. We review MBL replacement studies, and discuss the potential of MBL substitution therapy. We finally suggest that new MBL substitution trials should be conducted within a predefined patient population. MBL-deficiency should be based on serum levels and confirmed by genotyping.
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