SARS-CoV-2 Nucleocapsid Protein Is Not Responsible for Over-Activation of Complement Lectin Pathway.

The nucleocapsid (N) protein of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a viral structural protein that is abundant in the circulation of infected individuals. Previous published studies reported controversial data about the role of the N protein in the activation of the complement system. It was suggested that the N protein directly interacts with mannose-binding lectin-associated serine protease-2 (MASP-2) and stimulates lectin pathway overactivation/activity. In order to check these data and to reveal the mechanism of activation, we examined the effect of the N protein on lectin pathway activation. We found that the N protein does not bind to MASP-2 and MASP-1 and it does not stimulate lectin pathway activity in normal human serum. Furthermore, the N protein does not facilitate the activation of zymogen MASP-2, which is MASP-1 dependent. Moreover, the N protein does not boost the enzymatic activity of MASP-2 either on synthetic or on protein substrates. In some of our experiments, we observed that MASP-2 digests the N protein. However, it is questionable, whether this activity is biologically relevant. Although surface-bound N protein did not activate the lectin pathway, it did trigger the alternative pathway in 10% human serum. Additionally, we detected some classical pathway activation by the N protein. Nevertheless, we demonstrated that this activation was induced by the bound nucleic acid, rather than by the N protein itself.

Mannose-binding lectin gene 2 variant DD (rs 5030737) is associated with susceptibility to COVID-19 infection in the urban population of Patna City (India).

The study aimed to measure plasma levels of Mannose-Binding Lectin (MBL) and MBL-associated serine protease-2 (MASP-2) and their polymorphisms in COVID-19 patients and controls to detect association. As MBL is a protein of immunological importance, it may contribute to the first-line host defence against SARS-CoV-2. MBL initiates the lectin pathway of complement activation with help of MASP-1 and MASP-2. Hence, appropriate serum levels of MBL and MASPs are crucial in getting protection from the disease. The polymorphisms of MBL and MASP genes affect their plasma levels, impacting their protective function and thus may manifest susceptibility, extreme variability in the clinical symptoms and progression of COVID-19 disease. The present study was conducted to find plasma levels and genetic variations in MBL and MASP-2 in COVID-19 patients and controls using PCR-RFLP and ELISA, respectively.The present study was conducted to find plasma levels and genetic variations in MBL and MASP-2 in COVID-19 patients and controls using PCR-RFLP and ELISA, respectively. Our results indicate that median serum levels of MBL and MASP-2 were significantly low in diseased cases but attained normal levels on recovery. Only genotype DD was found to be associated with COVID-19 cases in the urban population of Patna city.

MASP2 inhibition by narsoplimab suppresses endotheliopathies characteristic of transplant-associated thrombotic microangiopathy: in vitro and ex vivo evidence.

Transplant-associated thrombotic microangiopathy (TA-TMA) is an endotheliopathy complicating up to 30% of allogeneic hematopoietic stem cell transplants (alloHSCT). Positive feedback loops among complement, pro-inflammatory, pro-apoptotic, and coagulation cascade likely assume dominant roles at different disease stages. We hypothesized that mannose-binding lectin-associated serine protease 2 (MASP2), principal activator of the lectin complement system, is involved in the microvascular endothelial cell (MVEC) injury characteristic of TA-TMA through pathways that are susceptible to suppression by anti-MASP2 monoclonal antibody narsoplimab. Pre-treatment plasmas from 8 of 9 TA-TMA patients achieving a complete TMA response in a narsoplimab clinical trial activated caspase 8, the initial step in apoptotic injury, in human MVEC. This was reduced to control levels following narsoplimab treatment in 7 of the 8 subjects. Plasmas from 8 individuals in an observational TA-TMA study, but not 8 alloHSCT subjects without TMA, similarly activated caspase 8, which was blocked in vitro by narsoplimab. mRNA sequencing of MVEC exposed to TA-TMA or control plasmas with and without narsoplimab suggested potential mechanisms of action. The top 40 narsoplimab-affected transcripts included upregulation of SerpinB2, which blocks apoptosis by inactivating procaspase 3; CHAC1, which inhibits apoptosis in association with mitigation of oxidative stress responses; and pro-angiogenesis proteins TM4SF18, ASPM, and ESM1. Narsoplimab also suppressed transcripts encoding pro-apoptotic and pro-inflammatory proteins ZNF521, IL1R1, Fibulin-5, aggrecan, SLC14A1, and LOX1, and TMEM204, which disrupts vascular integrity. Our data suggest benefits to narsoplimab use in high-risk TA-TMA and provide a potential mechanistic basis for the clinical efficacy of narsoplimab in this disorder.

Mannose binding lectin-associated serine protease 2 (MASP2) gene polymorphism and susceptibility to human T-lymphotropic virus type 1 (HTLV-1) infection in blood donors from Mashhad, Iran.

Mannose binding lectin-associated serine protease 2 (MASP2) is the effector part of mannose binding lectin (MBL) that activates the complement system in an antibody-independent manner. We aimed to investigate the role of genetic polymorphisms in the MASP2 gene and susceptibility to HTLV-1 infection. A total of 172 HTLV-1 infected individuals and 170 healthy blood donors were analyzed in this case-control study. Nine single nucleotide polymorphisms (SNPs) encompassing different regions of the MASP2 gene were genotyped with a polymerase chain reaction-sequence-specific primer (PCR-SSP) assay. The relation between the SNPs genotype and the susceptibility to HTLV-1 infection was investigated with a χ2 test considering P < 0.05 as statistically significant. Two of nine tested SNPs were associated with the risk of HTLV-1 infection. The genotype TT at rs17409276 decreased the risk of HTLV-1 (P = 0.005, OR = 0.301, 95% CI = 0.124-0.728). The genotypes CC and CT at rs2273346 were also associated with a higher risk of HTLV-1 acquisition (P = 0.004, OR = 2.225, 95% CI = 1.277-3.877). These findings highlight the importance of MASP2 genetic polymorphisms in the lectin pathway of complement activation and susceptibility to HTLV-1 infection.

Significance of Mannan Binding Lectin-Associated Serine Protease 2 in Urinary Extracellular Vesicles in IgA Nephropathy.

PURPOSE: Immunoglobulin A (IgA) nephropathy (IgAN) is a common chronic glomerulonephritis and the main cause of end-stage renal diseases. Recent evidence suggests that mannan binding lectin associated serine proteases 2 (MASP2) is related to IgAN; therefore, we investigated the expression and significance of MASP2 in serum and urinary extracellular vesicles (UEVs) in patients with IgAN. METHODS: Thirty-eight patients with IgAN and 17 healthy controls were enrolled in this study. UEVs were extracted by ultracentrifugation. The separation by ultra-high-speed centrifuge was verified by transmission electron microscopy (TEM) and nanoparticle tracking analysis (NTA). Candidate internal references (TSG101, CD9, flotillin, ß-actin and GAPDH) were identified by western blotting in the control group, and the expression of MASP2 in the UEVs was compared. The levels of MASP2 in the serum and UEVs in the IgAN and control groups were determined by enzyme-linked immunosorbent assay (ELISA). RESULTS: TEM and NTA results demonstrated that UEVs were successfully extracted. Western blotting results confirmed that TSG101 was suitable as an internal reference for this study. Compared with the control group, the IgAN group showed positive expression of MASP2. MASP2 levels in the UEVs, determined by ELISA, showed significant differences between IgAN and control groups, which were significantly positively correlated with the level of urinary microalbumin. CONCLUSIONS: The level of MASP2 in UEVs was related to IgAN and shows promise as a biomarker for evaluating the severity of renal injury and prognosis of IgAN, thereby helping to elucidate the role of MASP2 in the mannan-binding lectin pathway.

Association of MASP2 levels and MASP2 gene polymorphisms with systemic lupus erythematosus.

Systemic lupus erythematosus (SLE) is a chronic inflammatory autoimmune disorder. MASP2 is a mediator that plays an important role in complement system. As dysregulation of the complement system has been demonstrated to correlate with SLE pathogenesis, the role of MASP2 in lupus has not been widely discussed. In the present study, serum levels of MASP2 were evaluated in 61 lupus patients and 98 healthy controls by training cohort, and then a validation cohort including 100 lupus, 100 rheumatoid arthritis, 100 osteoarthritis, 100 gout, 44 Sjogren's syndrome, 41 ankylosing spondylitis patients confirmed the findings. Receiver operating characteristic (ROC) curve analysis determined the discriminatory capacity for serum MASP2. PCR methods tested the association of MASP2 gene polymorphisms (rs7548659, rs17409276, rs2273346, rs1782455 and rs6695096) and SLE risk. Impact of polymorphism on MASP2 serum levels was evaluated as well. Results showed that serum levels of MASP2 were significantly higher in lupus patients and correlated with some clinical, laboratory characteristics in the training cohort, and were much higher as compared to that in different rheumatic diseases patients in the validation cohort. Serum MASP2 showed a good diagnostic ability for lupus. Genotype frequencies and allele frequency of polymorphisms rs7548659, rs2273346 were strongly related to SLE risk, and genotypes of rs17409276, rs1782455, rs76695096 were significantly correlated with lupus genetic susceptibility. Interestingly, patients carrying GA genotype of rs17409276, TT, TC genotype of rs6695096 showed higher levels of serum MASP2. The findings suggested that MASP2 may be a potential disease marker for lupus, and correlate with SLE pathogenesis.

Novel MASP-2 inhibitors developed via directed evolution of human TFPI1 are potent lectin pathway inhibitors.

The lectin pathway (LP) of the complement system is an important antimicrobial defense mechanism, but it also contributes significantly to ischemia reperfusion injury (IRI) associated with myocardial infarct, stroke, and several other clinical conditions. Mannan-binding lectin-associated serine proteinase 2 (MASP-2) is essential for LP activation, and therefore, it is a potential drug target. We have previously developed the first two generations of MASP-2 inhibitors by in vitro evolution of two unrelated canonical serine proteinase inhibitors. These inhibitors were selective LP inhibitors, but their nonhuman origin rendered them suboptimal lead molecules for drug development. Here, we present our third-generation MASP-2 inhibitors that were developed based on a human inhibitor scaffold. We subjected the second Kunitz domain of human tissue factor pathway inhibitor 1 (TFPI1 D2) to directed evolution using phage display to yield inhibitors against human and rat MASP-2. These novel TFPI1-based MASP-2 inhibitor (TFMI-2) variants are potent and selective LP inhibitors in both human and rat serum. Directed evolution of the first Kunitz domain of TFPI1 had already yielded the potent kallikrein inhibitor, Kalbitor® (ecallantide), which is an FDA-approved drug to treat acute attacks of hereditary angioedema. Like hereditary angioedema, acute IRI is also related to the uncontrolled activation of a specific plasma serine proteinase. Therefore, TFMI-2 variants are promising lead molecules for drug development against IRI.

Anti-complement C5 therapy with eculizumab in three cases of critical COVID-19.

Respiratory failure and acute kidney injury (AKI) are associated with high mortality in SARS-CoV-2-associated Coronavirus disease 2019 (COVID-19). These manifestations are linked to a hypercoaguable, pro-inflammatory state with persistent, systemic complement activation. Three critical COVID-19 patients recalcitrant to multiple interventions had skin biopsies documenting deposition of the terminal complement component C5b-9, the lectin complement pathway enzyme MASP2, and C4d in microvascular endothelium. Administration of anti-C5 monoclonal antibody eculizumab led to a marked decline in D-dimers and neutrophil counts in all three cases, and normalization of liver functions and creatinine in two. One patient with severe heart failure and AKI had a complete remission. The other two individuals had partial remissions, one with resolution of his AKI but ultimately succumbing to respiratory failure, and another with a significant decline in FiO2 requirements, but persistent renal failure. In conclusion, anti-complement therapy may be beneficial in at least some patients with critical COVID-19.

Should MASP-2 Deficiency Be Considered a Primary Immunodeficiency? Relevance of the Lectin Pathway.

Mannose-binding lectin (MBL)-associated serine protease-2 (MASP-2) is an indispensable enzyme for the activation of the lectin pathway of complement. Its deficiency is classified as a primary immunodeficiency associated to pyogenic bacterial infections, inflammatory lung disease, and autoimmunity. In Europeans, MASP-2 deficiency, due to homozygosity for c.359A > G (p.D120G), occurs in 7 to 14/10,000 individuals. We analyzed the presence of the p.D120G mutation in adults (increasing the sample size of our previous studies) and children. Different groups of patients (1495 adults hospitalized with community-acquired pneumonia, 186 adults with systemic lupus erythematosus, 103 pediatric patients with invasive pneumococcal disease) and control individuals (1119 healthy adult volunteers, 520 adult patients without history of relevant infectious diseases, and a pediatric control group of 311 individuals) were studied. Besides our previously reported MASP-2-deficient healthy adults, we found a new p.D120G homozygous individual from the pediatric control group. We also reviewed p.D120G homozygous individuals reported so far: a total of eleven patients with a highly heterogeneous range of disorders and nine healthy controls (including our four MASP-2-deficient individuals) have been identified by chance in association studies. Individuals with complete deficiencies of several pattern recognition molecules of the lectin pathway (MBL, collectin-10 and collectin-11, and ficolin-3) as well as of MASP-1 and MASP-3 have also been reviewed. Cumulative evidence suggests that MASP-2, and even other components of the LP, are largely redundant in human defenses and that individuals with MASP-2 deficiency do not seem to be particularly prone to infectious or autoimmune diseases.

Is Early Complement Activation in Renal Transplantation Associated with Later Graft Outcome?

BACKGROUND/AIMS: Complement activation is important in post-transplantation renal injury, but data on its role as predictor of transplant outcome/complications when assessed in donor kidneys are lacking. METHODS: In human renal transplant biopsies with delayed graft function (DGF, n=12), antibody mediated rejection (ABMR, n=8), T-cell mediated rejection (TCMR, n=11), 1 year protocol biopsies (control, n=10) and corresponding zero-biopsies we performed immunohistochemical analyses of 6 complement factors using FFPE sections and correlated the findings with kidney function, as assessed by serum creatinine, and morphological changes including interstitial fibrosis and tubular atrophy (IF/TA). RESULTS: In DGF, TCMR and ABMR significant complement deposition was observed, which was less pronounced in corresponding zero-biopsies. Zero-biopsies with subsequent ABMR showed glomerular complement factor D and C3c expression. Moreover, glomerular C3c and C9 and tubular MASP-2 and Collectin-11 expression in zero-biopsies significantly correlated with serum creatinine at diagnosis of DGF, TCMR or ABMR. Glomerular C1q was significantly increased in ABMR, but not in DGF and TCMR. In contrast, peritubular C1q was significantly enhanced in DGF and TCMR compared to zero-biopsies. Using C3d as a surrogate marker for complement activity we could confirm that stained complement factors are frequently associated with complement activity. CONCLUSION: Complement deposition strongly correlated with histopathological changes observed in renal transplants. All 3 complement pathways were operational in biopsies with DGF, TCMR and ABMR albeit with differential abundance and localization. Since complement deposition in zero-biopsies correlated with graft function and morphological changes, early specific complement inhibition in renal transplantation may be a new therapeutic option to prevent graft loss.

Effects of MASP2 haplotypes and MASP-2 levels in hepatitis C-infected patients.

Mannan-binding lectin (MBL) and MBL-associated serine protease 2 (MASP-2) are components of the lectin pathway, which activate the complement system after binding to the HCV structural proteins E1 and E2. We haplotyped 11 MASP2 polymorphisms in 103 HCV patients and 205 controls and measured MASP-2 levels in 67 HCV patients and 77 controls to better understand the role of MASP-2 in hepatitis C susceptibility and disease severity according to viral genotype and fibrosis levels. The haplotype block MASP2*ARDP was associated with protection against HCV infection (OR = 0.49, p = .044) and lower MASP-2 levels in controls (p = .021), while haplotype block AGTDVRC was significantly increased in patients (OR = 7.58, p = .003). MASP-2 levels were lower in patients than in controls (p < .001) and in patients with viral genotype 1 or 4 (poor responders to treatment) than genotype 3 (p = .022) and correlated inversely with the levels of alkaline phosphatase, especially in individuals with fibrosis 3 or 4 (R = -.7, p = .005). MASP2 gene polymorphisms modulate basal gene expression, which may influence the quality of complement response against HCV. MASP-2 levels decrease during chronic disease, independently of MASP2 genotypes, most probably due to consumption and attenuation mechanisms of viral origin and by the reduced liver function, the site of MASP-2 production.

Construction of human MASP-2-CCP1/2SP, CCP2SP, SP plasmid DNA nanolipoplexes and the effects on tuberculosis in BCG-infected mice.

The lectin pathway, one of the complement cascade systems, provides the primary line of defense against invading pathogens. The serine protease of MASP-2 plays an essential role in complement activation of the lectin pathway. The C-terminal segment of MASP-2 is comprised of the CCP1-CCP2-SP domains, and is the crucial catalytic segment. However, what is the effect of CCP1-CCP2-SP domains in controlling chronic infection is unknown. In order to evaluate the potential impact of CCP1-CCP2-SP domains on tuberculosis, we constructed the human MASP-2 CCP1/2SP, CCP2SP and SP recombinant plasmids, and delivered these plasmids by DNA-DOTAP:cholesterol cationic nanolipoplexes to BCG-infected mice. After 21 days post DNA-DOTAP:chol nanolipoplexes application, we analyzed bacteria loads of pulmonary, pathology of granuloma, lymphocyte subpopulations. The C3a, C4a and MASP-2 levels in serum were measured with enzyme-linked immunosorbent assays. Compared to the control group that received GFP DNA-DOTAP:chol nanolipoplexes, MASP-2 CCP1/2SP DNA-DOTAP:chol nanolipoplexes treated group showed significantly enlarged pulmonary granulomas lesion (P < 0.05) and did not reduce bacteria loads in the lung tissue (P < 0.05). Furthermore, the levels of C3a in serum were decreased (P < 0.05), the number and percentage of PD1+ and Tim3+ cells subgroups were increased in BCG-infected mice after treated with MASP-2 CCP1/2SP DNA-DOTAP:chol nanolipoplexes (P < 0.05). But, there was no statistical difference in the serum C4a and MASP-2 level among DNA nanolipoplexes treated groups (P > 0.05). These findings provided experimental evidence that MASP-2 CCP1/2SP DNA nanolipoplexes shown the negative efficacy in controlling Mycobacterium tuberculosis infection, and displayed a potential role of down-regulating T-cell-mediated immunity in tuberculosis.

TFPI inhibits lectin pathway of complement activation by direct interaction with MASP-2.

The lectin pathway (LP) of complement has a protective function against invading pathogens. Recent studies have also shown that the LP plays an important role in ischemia/reperfusion (I/R)-injury. MBL-associated serine protease (MASP)-2 appears to be crucial in this process. The serpin C1-inhibitor is the major inhibitor of MASP-2. In addition, aprotinin, a Kunitz-type inhibitor, was shown to inhibit MASP-2 activity in vitro. In this study we investigated whether the Kunitz-type inhibitor tissue factor pathway inhibitor (TFPI) is also able to inhibit MASP-2. Ex vivo LP was induced and detected by C4-deposition on mannan-coated plates. The MASP-2 activity was measured in a fluid-phase chromogenic assay. rTFPI in the absence or presence of specific monoclonal antibodies was used to investigate which TFPI-domains contribute to MASP-2 inhibition. Here, we identify TFPI as a novel selective inhibitor of MASP-2, without affecting MASP-1 or the classical pathway proteases C1s and C1r. Kunitz-2 domain of TFPI is required for the inhibition of MASP-2. Considering the role of MASP-2 in complement-mediated I/R-injury, the inhibition of this protease by TFPI could be an interesting therapeutic approach to limit the tissue damage in conditions such as cerebral stroke, myocardial infarction or solid organ transplantation.

Frequency and distribution of FCN2 and FCN3 functional variants among MBL2 genotypes.

The six types of pattern recognition molecules (PRMs) that initiate complement via the lectin pathway (LP) comprise collectins and ficolins. The importance of having various PRMs to initiate the LP is currently unclear. Mannan-binding lectin (MBL) is a collectin member of the LP PRMs. MBL deficiency is common with mild clinical consequence. Thus, the lack of MBL may be compensated for by the other PRMs. We hypothesized that variants FCN2 + 6424 and FCN3 + 1637delC that cause gene-dose-dependent reduction in ficolin-2 and ficolin-3 levels, respectively, may be rare in MBL-deficient individuals due to the importance of compensation within the LP. The aim of this study was to investigate the distribution and frequency of these variants among MBL2 genotypes in healthy subjects. The allele frequency of FCN2 + 6424 and FCN3 + 1637delC was 0.099 and 0.015, respectively, in the cohort (n = 498). The frequency of FCN2 + 6424 tended to be lower among MBL-deficient subjects (n = 53) than among MBL-sufficient subjects (n = 445) (0.047 versus 0.106, P = 0.057). In addition, individuals who were homozygous for FCN2 + 6424 were sufficient MBL producers. The frequency of FCN3 + 1637delC did not differ between the groups. The frequency of FCN2 + 6424 was similar in FCN3 + 1637delC carriers (n = 15) versus wild type (n = 498). Furthermore, subjects that were heterozygote carriers of both FCN2 + 6424 and FCN3 + 1637delC were sufficient MBL producers. In conclusion, FCN2 + 6424 carriers with MBL deficiency tend to be rare among healthy individuals. MBL-deficient individuals with additional LP PRM defects may be at risk to morbidity.

Plasma levels of mannan-binding lectin-associated serine proteases MASP-1 and MASP-2 are elevated in type 1 diabetes and correlate with glycaemic control.

There is increasing evidence that the complement system plays an important role in diabetes and the development of diabetic vascular complications. In particular, mannan-binding lectin (MBL) levels are elevated in diabetes patients, and diabetes patients with diabetic nephropathy have higher MBL levels than diabetes patients with normal renal function. The MBL-associated serine proteases (MASPs) MASP-1, MASP-2 and MASP-3 and MBL-associated protein MAp44 have not yet been studied in diabetes patients. We therefore measured plasma levels of MASP-1, MASP-2, MASP-3 and MAp44 in 30 children with type 1 diabetes mellitus (T1DM) and 17 matched control subjects, and in 45 adults with T1DM and 31 matched control subjects. MASP-1 and MASP-2 levels were significantly higher in children and adults with T1DM than in their respective control groups, whereas MASP-3 and MAp44 levels did not differ between patients and controls. MASP-1 and MASP-2 levels correlated with HbA1c, and MASP levels decreased when glycaemic control improved. Because MASP-1 and MASP-2 have been shown to interact directly with blood coagulation, elevated levels of these proteins may play a role in the enhanced thrombotic environment and consequent vascular complications in diabetes.

Low MBL-associated serine protease 2 (MASP-2) levels correlate with urogenital schistosomiasis in Nigerian children.

OBJECTIVES: The human mannose-binding lectin (MBL) and ficolins (FCN) are involved in pathogen recognition in the first line of defence. They support activation of the complement lectin cascade in the presence of MBL-associated serine protease 2 (MASP-2), a protein that cleaves the C4 and C2 complement components. Recent studies found that distinct MBL2 and FCN2 promoter variants and their corresponding serum levels are associated with relative protection from urogenital schistosomiasis. METHODS: We investigated the contribution of MASP-2 levels and MASP2 polymorphisms in a Nigerian study group, of 163 individuals infected with Schistosoma haematobium and 183 healthy subjects. RESULTS: MASP-2 serum levels varied between younger children (≤12 years) and older children (>12 years) and adults (P = 0.0001). Younger children with a patent infection had significantly lower MASP-2 serum levels than uninfected children (P = 0.0074). Older children and adults (>12 years) with a current infection had higher serum MASP-2 levels than controls (P = 0.032). MBL serum levels correlated positively with MASP-2 serum levels (P = 0.01). MASP2 secretor haplotypes were associated with MASP-2 serum levels in healthy subjects. The heterozygous MASP2 p.P126L variant was associated with reduced serum MASP-2 levels (P = 0.01). CONCLUSIONS: The findings indicate that higher MASP-2 serum levels are associated with relative protection from urogenital schistosomiasis in Nigerian children.

Revisiting the interaction between complement lectin pathway protease MASP-2 and SARS-CoV-2 nucleoprotein.

Complement activation is considered to contribute to the pathogenesis of severe SARS-CoV-2 infection, mainly by generating potent immune effector mechanisms including a strong inflammatory response. Involvement of the lectin complement pathway, a major actor of the innate immune anti-viral defense, has been reported previously. It is initiated by recognition of the viral surface Spike glycoprotein by mannose-binding lectin (MBL), which induces activation of the MBL-associated protease MASP-2 and triggers the proteolytic complement cascade. A role for the viral nucleoprotein (N) has also been reported, through binding to MASP-2, leading to protease overactivation and potentiation of the lectin pathway. In the present study, we reinvestigated the interactions of the SARS-CoV-2 N protein, produced either in bacteria or secreted by mammalian cells, with full-length MASP-2 or its catalytic domain, in either active or proenzyme form. We could not confirm the interaction of the N protein with the catalytic domain of MASP-2 but observed N protein binding to proenzyme MASP-2. We did not find a role of the N protein in MBL-mediated activation of the lectin pathway. Finally, we showed that incubation of the N protein with MASP-2 results in proteolysis of the viral protein, an observation that requires further investigation to understand a potential functional significance in infected patients.

Compassionate Use Narsoplimab for Severe Refractory Transplantation-Associated Thrombotic Microangiopathy in Children.

Transplant-associated thrombotic microangiopathy (TA-TMA) is a common and potentially severe complication of hematopoietic cell transplantation. TA-TMA-directed therapy with eculizumab, a complement C5 inhibitor, has resulted in a survival benefit in some studies. However, children with TA-TMA refractory to C5 inhibition with eculizumab (rTA-TMA) have mortality rates exceeding 80%, and there are no other known therapies. Narsoplimab, an inhibitor of the MASP-2 effector enzyme of the lectin pathway, has been studied in adults with TA-TMA as first-line therapy with a response rate of 61%. Although there are limited data on narsoplimab use as a second-line agent in children, we hypothesized, that complement pathways proximal to C5 are activated in rTA-TMA, and that narsoplimab may ameliorate rTA-TMA in children. In this single-center study, children were enrolled on single-patient, Institutional Review Board-approved compassionate use protocols for narsoplimab treatment. Clinical complement lab tests were obtained at the discretion of the treating physician, although all patients were also offered participation in a companion biomarker study. Research blood samples were obtained at the time of TA-TMA diagnosis, prior to eculizumab treatment, at the time of refractory TA-TMA diagnosis prior to the first narsoplimab dose, and 2 weeks after the first narsoplimab dose. Single ELISA kits were used to measure markers of complement activation according to the manufacture's instructions. Five children with rTA-TMA received narsoplimab; 3 were in multiorgan failure and 2 had worsening multiorgan dysfunction at the time of treatment. Additional comorbidities at the time of treatment included sinusoidal obstructive syndrome (SOS; n = 3), viral infection (n = 3), and steroid-refractory stage 4 lower gut grade IV acute graft-versus-host disease (aGVHD, n = 3). Two infants with concurrent SOS and no aGVHD had resolution of organ dysfunction; 1 also developed transfusion-independence (complete response), and the other's hematologic response was not assessable in the setting of leukemia and chemotherapy (partial response). One additional patient achieved transfusion independence but had no improvement in organ manifestations (partial response), and 2 patients treated late in the course of disease had no response. Narsoplimab was well tolerated without any attributed adverse effects. Three patients consented to provide additional research blood samples. One patient with resolution of organ failure demonstrated evidence of proximal pathway activation prior to narsoplimab treatment with subsequent declines in Ba, Bb, C3a, and C5a and increases in C3 in both clinical and research lab tests. Otherwise, there was no clear pattern of other complement markers, including MASP-2 levels, after therapy. In this cohort of ill children with rTA-TMA and multiple comorbidities, 3 patients benefited from narsoplimab. Notably, the 2 patients with resolution of organ involvement did not have steroid-refractory aGVHD, which is thought to be a critical driver of TA-TMA. Additional studies are needed to determine which patients are most likely to benefit from narsoplimab and which markers may be most helpful for monitoring lectin pathway activation and inhibition.

Mannose binding lectin and mannose binding lectin-associated serine protease-2 genes polymorphisms in human T-lymphotropic virus infection.

Variations in genes involved in the immune response pathways may influence the interaction between viruses (such as Human T-lymphotropic virus, HTLV-1) and the host. The mannose binding lectin (MBL) and its associated serine protease type 2 (MASP-2) promote the activation of the lectin pathway of the complement system. As the interaction of complement system with HTLV-1 is not well understood, the MBL2 promoter/exon 1 polymorphisms and a MASP2 missense polymorphism were examined in a Northeast Brazilian population, looking for a possible relationship between these variations and the susceptibility to HTLV-1 infection. The present study describes an association between a polymorphism in the MASP2 gene and susceptibility to HTLV-1 infection, and provides further evidence of an association between the MBL2 gene and HTLV-1 infection. These findings suggest an important role of the complement system activation, via the lectin pathway, in the susceptibility to HTLV-1 infection.

Development and characterization of narsoplimab, a selective MASP-2 inhibitor, for the treatment of lectin-pathway-mediated disorders.

Introduction: Overactivation of the lectin pathway of complement plays a pathogenic role in a broad range of immune-mediated and inflammatory disorders; mannan-binding lectin-associated serine protease-2 (MASP-2) is the key effector enzyme of the lectin pathway. We developed a fully human monoclonal antibody, narsoplimab, to bind to MASP-2 and specifically inhibit lectin pathway activation. Herein, we describe the preclinical characterization of narsoplimab that supports its evaluation in clinical trials. Methods and results: ELISA binding studies demonstrated that narsoplimab interacted with both zymogen and enzymatically active forms of human MASP-2 with high affinity (KD 0.062 and 0.089 nM, respectively) and a selectivity ratio of >5,000-fold relative to closely related serine proteases C1r, C1s, MASP-1, and MASP-3. Interaction studies using surface plasmon resonance and ELISA demonstrated approximately 100-fold greater binding affinity for intact narsoplimab compared to a monovalent antigen binding fragment, suggesting an important contribution of functional bivalency to high-affinity binding. In functional assays conducted in dilute serum under pathway-specific assay conditions, narsoplimab selectively inhibited lectin pathway-dependent activation of C5b-9 with high potency (IC50 ~ 1 nM) but had no observable effect on classical pathway or alternative pathway activity at concentrations up to 500 nM. In functional assays conducted in 90% serum, narsoplimab inhibited lectin pathway activation in human serum with high potency (IC50 ~ 3.4 nM) whereas its potency in cynomolgus monkey serum was approximately 10-fold lower (IC50 ~ 33 nM). Following single dose intravenous administration to cynomolgus monkeys, narsoplimab exposure increased in an approximately dose-proportional manner. Clear dose-dependent pharmacodynamic responses were observed at doses >1.5 mg/kg, as evidenced by a reduction in lectin pathway activity assessed ex vivo that increased in magnitude and duration with increasing dose. Analysis of pharmacokinetic and pharmacodynamic data revealed a well-defined concentration-effect relationship with an ex vivo EC50 value of approximately 6.1 µg/mL, which was comparable to the in vitro functional potency (IC50 33 nM; ~ 5 µg/mL). Discussion: Based on these results, narsoplimab has been evaluated in clinical trials for the treatment of conditions associated with inappropriate lectin pathway activation, such as hematopoietic stem cell transplantation-associated thrombotic microangiopathy.