Mannan-binding lectin insufficiency in children with recurrent infections of the respiratory system.
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Blood samples were collected over a 4-year period from 335 children (aged 1-16 years) suffering from recurrent respiratory infections and 78 controls. The patients were subdivided into four groups: I, children with no immune system defects detected (n = 101); II, children with allergies (n = 94); III, children with humoral response defects (n = 93); and IV, children with disturbances of cellular immunity (n = 66). Nineteen patients had both humoral and cellular abnormalities. All patients and controls were investigated to determine the exon 1 and promoter region variants of the mbl-2 gene. MBL serum concentrations were also determined in samples from 291 patients and 75 controls. The proportion of O (B, D or C) alleles was significantly higher in the patient group compared to controls, and this association was strongest for subgroup III. The promoter LX variant frequency was also commoner in the patients as a whole, and significantly so in subgroups II and IV. Genotypes markedly influenced MBL concentrations in all groups, and correlated with ability to activate the lectin pathway of complement activation. The strongest and most significant inverse correlations between serum MBL and respiratory disease were found in patient group III and in 17 patients with multiple humoral and/or cellular abnormalities. Among nine patients with unexpectedly low LP activity in view of their MBL concentrations, one person was found to be MASP-2 deficient. Our results indicate that mannan-binding lectin insufficiency, with or without a coexisting immune defect, is associated with the occurrence of recurrent respiratory infections in childhood, and this relationship is particularly strong and statistically significant in children with concomitant impairments of humoral immunity. (+info)
Cloning and characterization of a novel mannose-binding protein of Acanthamoeba.
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Acanthamoebae produce a painful, blinding infection of the cornea. The mannose-binding protein (MBP) of Acanthamoeba is thought to play a key role in the pathogenesis of the infection by mediating the adhesion of parasites to the host cells. We describe here the isolation and molecular cloning of Acanthamoeba MBP. The MBP was isolated by chromatography on the mannose affinity gel. Gel filtration experiments revealed that the Acanthamoeba lectin is a approximately 400-kDa protein that is constituted of multiple 130-kDa subunits. Cloning and sequencing experiments indicated that the Acanthamoeba MBP gene is composed of 6 exons and 5 introns that span 3.6 kb of the amoeba genome and that MBP cDNA codes for a precursor protein of 833 amino acids. That the cloned cDNA encodes authentic MBP was demonstrated by showing that: (i). recombinant MBP possesses mannose binding activity, and (ii). polyclonal antibodies prepared against Acanthamoeba MBP bound to the recombinant protein. Sequence analysis revealed that the MBP contains a large N-terminal extracellular domain, a transmembrane domain, and a short C-terminal cytoplasmic domain. Despite extensive BLAST searches using the MBP sequence, no significant matches were retrieved. The most striking feature of the Acanthamoeba MBP sequence is the presence of a cysteine-rich region containing 14 CXCXC motifs within the extracellular domain. In summary, we have isolated, cloned, and characterized a novel MBP from Acanthamoeba. Because the presence of antibodies to MBP in tears provides protection against infection, the availability of the MBP cDNA sequence and rMBP should help develop: (i). a tear-based test to identify individuals who are at risk of developing the keratitis and (ii). strategies to immunize high-risk individuals. (+info)
The X-ray structure of human mannan-binding lectin-associated protein 19 (MAp19) and its interaction site with mannan-binding lectin and L-ficolin.
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MAp19 is an alternative splicing product of the MASP-2 gene comprising the N-terminal CUB1-epidermal growth factor (EGF) segment of MASP-2, plus four additional residues at its C-terminal end. Like full-length MASP-2, it forms Ca(2+)-dependent complexes with mannan-binding lectin (MBL) and L-ficolin. The x-ray structure of human MAp19 was solved to a resolution of 2.5 A. It shows a head to tail homodimer held together by interactions between the CUB1 module of one monomer and the EGF module of its counterpart. A Ca(2+) ion bound to each EGF module stabilizes the dimer interfaces. A second Ca(2+) ion is bound to the distal end of each CUB1 module, through six ligands contributed by Glu(52), Asp(60), Asp(105), Ser(107), Asn(108), and a water molecule. Compared with its counterpart in human C1s, the N-terminal end of the MAp19 CUB1 module contains a 7-residue extension that forms additional inter-monomer contacts. To identify the residues involved in the interaction of MAp19 with MBL and L-ficolin, point mutants were generated and their binding ability was determined using surface plasmon resonance spectroscopy. Six mutations at Tyr(59), Asp(60), Glu(83), Asp(105), Tyr(106), and Glu(109) either strongly decreased or abolished interaction with both MBL and L-ficolin. These mutations map a common binding site for these proteins located at the distal end of each CUB1 module and stabilized by the Ca(2+) ion. (+info)
Nucleic acid is a novel ligand for innate, immune pattern recognition collectins surfactant proteins A and D and mannose-binding lectin.
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Collectins are a family of innate immune proteins that contain fibrillar collagen-like regions and globular carbohydrate recognition domains (CRDs). The CRDs of these proteins recognize various microbial surface-specific carbohydrate patterns, particularly hexoses. We hypothesized that collectins, such as pulmonary surfactant proteins (SPs) SP-A and SP-D and serum protein mannose-binding lectin, could recognize nucleic acids, pentose-based anionic phosphate polymers. Here we show that collectins bind DNA from a variety of origins, including bacteria, mice, and synthetic oligonucleotides. Pentoses, such as arabinose, ribose, and deoxyribose, inhibit the interaction between SP-D and mannan, one of the well-studied hexose ligands for SP-D, and biologically relevant d-forms of the pentoses are better competitors than the l-forms. In addition, DNA and RNA polymer-related compounds, such as nucleotide diphosphates and triphosphates, also inhibit the carbohydrate binding ability of SP-D, or approximately 60 kDa trimeric recombinant fragments of SP-D that are composed of the alpha-helical coiled-coil neck region and three CRDs (SP-D(n/CRD)) or SP-D(n/CRD) with eight GXY repeats (SPD(GXY)(8)(n/CRD)). Direct binding and competition studies suggest that collectins bind nucleic acid via their CRDs as well as by their collagen-like regions, and that SP-D binds DNA more effectively than do SP-A and mannose-binding lectin at physiological salt conditions. Furthermore, the SP-D(GXY)(8)(n/CRD) fragments co-localize with DNA, and the protein competes the interaction between propidium iodide, a DNA-binding dye, and apoptotic cells. In conclusion, we show that collectins are a new class of proteins that bind free DNA and the DNA present on apoptotic cells by both their globular CRDs and collagen-like regions. Collectins may therefore play an important role in decreasing the inflammation caused by DNA in lungs and other tissues. (+info)
Human Mannose-binding Lectin in Immunity: Friend, Foe, or Both?
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Human mannose-binding lectin (MBL) recognizes a wide range of microorganisms and triggers the most ancient pathway of complement activation. However, approximately 5% of individuals lack functional serum MBL and have not been found to be prone to severe infections in prospective studies. These data suggest that human MBL is largely redundant for protective immunity and may even have been subject to counter selection because of a deleterious impact. (+info)
Mannose-binding lectin-deficient mice are susceptible to infection with Staphylococcus aureus.
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Gram-positive organisms like Staphylococcus aureus are a major cause of morbidity and mortality worldwide. Humoral response molecules together with phagocytes play a role in host responses to S. aureus. The mannose-binding lectin (MBL, also known as mannose-binding protein) is an oligomeric serum molecule that recognizes carbohydrates decorating a broad range of infectious agents including S. aureus. Circumstantial evidence in vitro and in vivo suggests that MBL plays a key role in first line host defense. We tested this contention directly in vivo by generating mice that were devoid of all MBL activity. We found that 100% of MBL-null mice died 48 h after exposure to an intravenous inoculation of S. aureus compared with 45% mortality in wild-type mice. Furthermore, we demonstrated that neutrophils and MBL are required to limit intraperitoneal infection with S. aureus. Our study provides direct evidence that MBL plays a key role in restricting the complications associated with S. aureus infection in mice and raises the idea that the MBL gene may act as a disease susceptibility gene against staphylococci infections in humans. (+info)
A population-based study of morbidity and mortality in mannose-binding lectin deficiency.
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Reduced levels of wild-type mannose-binding lectin (MBL) may increase susceptibility for infection, other common diseases, and death. We investigated associations between MBL deficiency and risk of infection, other common diseases, and death during 24, 24, and 8 yr of follow-up, respectively. We genotyped 9,245 individuals from the adult Danish population for three MBL deficiency alleles, B, C, and D, as opposed to the normal noncarrier A allele. Hospitalization incidence per 10,000 person. yr was 644 in noncarriers compared with 631 in heterozygotes (log-rank: P = 0.39) and 658 in deficiency homozygotes (P = 0.53). Death incidence per 10,000 person. yr was 235 in noncarriers compared with 244 in heterozygotes (P = 0.44) and 274 in deficiency homozygotes (P = 0.12). After stratification by specific cause of hospitalization or death, only hospitalization from cardiovascular disorders was increased in deficiency homozygotes versus noncarriers (P = 0.02). When retested in two case control studies, this association could not be confirmed. Incidence of hospitalization or death from infections or other serious common disorders did not differ between deficiency homozygotes and noncarriers. In conclusion, in this large study in an ethnically homogeneous Caucasian population, there was no evidence for significant differences in infectious disease or mortality in MBL-deficient individuals versus controls. Our results suggest that MBL deficiency is not a major risk factor for morbidity or death in the adult Caucasian population. (+info)
Association between mannose-binding lectin and vascular complications in type 1 diabetes.
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Complement activation and inflammation have been suggested in the pathogenesis of diabetic vascular lesions. We investigated serum mannose-binding lectin (MBL) levels and polymorphisms in the MBL gene in type 1 diabetic patients with and without diabetic nephropathy and associated macrovascular complications. Polymorphisms in the MBL gene and serum MBL levels were determined in 199 type 1 diabetic patients with overt nephropathy and 192 type 1 diabetic patients with persistent normoalbuminuria matched for age, sex, and duration of diabetes, as well as in 100 healthy control subjects. The frequencies of high- and low-expression MBL genotypes were similar in patients with type 1 diabetic and healthy control subjects. High MBL genotypes were significantly more frequent in diabetic patients with nephropathy than in the normoalbuminuric group, and the risk of having nephropathy given a high MBL genotype assessed by odds ratio (OR) was 1.52 (1.02-2.27, P = 0.04). Median serum MBL concentrations were significantly higher in patients with nephropathy than in patients with normoalbuminuria: 2,306 microg/l (interquartile range [IQR] 753-4,867 microg/l) vs. 1,491 microg/l (577-2,944 microg/l), P = 0.0003. In addition, even when comparing patients with identical genotypes, serum MBL levels were higher in the nephropathy group than in the normoalbuminuric group. Patients with a history of cardiovascular disease had significantly elevated MBL levels independent of nephropathy status (3,178 microg/l [IQR 636-5,231 microg/l] vs. 1,741 microg/l [656-3,149 microg/l], P = 0.02). The differences in MBL levels between patients with and without vascular complications were driven primarily by pronounced differences among carriers of high MBL genotypes (P < 0.0001). Our findings suggest that MBL may be involved in the pathogenesis of micro- and macrovascular complications in type 1 diabetes, and that determination of MBL status might be used to identify patients at increased risk of developing these complications. (+info)