Mannose-binding lectin deficiency - revisited

Department of Clinical Immunology, Tissue Typing Laboratory-7631, Rigshospitalet, Blegdamsvej 9, DK-2100 Copenhagen, Denmark.
Molecular Immunology (Impact Factor: 3). 10/2003; 40(2-4):73-84. DOI: 10.1016/S0161-5890(03)00104-4
Source: PubMed

ABSTRACT There is an emerging interest for mannose-binding lectin (MBL) due to its role in innate immunity. In this survey we present a mixture of old and new data describing the effect MBL polymorphisms may have on the level and function of the molecule. Three single nucleotide substitutions in exon 1 of the mbl2 gene cause a dominant decrease of functional MBL in the circulation. Additionally, promoter variants influence expression of MBL. It has been assumed that the structural variant alleles may disrupt the assembly of MBL trimers or accelerate the degradation of the protein, thereby causing the decrease in MBL serum concentrations. We have analysed 1183 different sera in a double sandwich antibody ELISA using the same antibody to capture and detect MBL and find the same results as have been presented previously showing that different MBL promoter alleles have profound effect of on the MBL serum concentration. The use of a new anti-MBL monoclonal antibody, however, has shown that the amount of MBL in the circulation is less dependent on the presence of structural variant alleles than previously anticipated. Molecular characterisation of MBL revealed that sera from donors homozygous for the normal MBL genotype predominantly contained high molecular weight MBL, while sera from individuals heterozygous for the variant alleles contained both high and low molecular weight MBL. The ratio between high and low molecular weight MBL was dependent on the MBL promoter type on the normal haplotype. Sera deriving from individuals homozygous for MBL variant alleles contained mainly low molecular weight MBL. Of the different oligomers of MBL only the high molecular weight forms bound mannan efficiently and activated complement. In contrast to a previous notion, we demonstrate that variant alleles give rise to relatively high levels of MBL in the circulation. However, the variant MBL has lower molecular weight and is dysfunctional compared to normal MBL. The physiological relevance of variant MBL remains to be established.

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    • "The presence of the X allele at position − 221 of the MBL2 promoter produces a lower amount of circulating MBL than that found in the presence of the Y allele. In addition, missense mutations in exon 1 abolish the assembly of the protein into its biologically active form [6] [7] [8]. "
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    ABSTRACT: Background There is a considerable variation in the phenotype and course of the disease in cystic fibrosis (CF) even in patients with the same CFTR genotype, suggesting that other factors are important for prognosis. Mannose-binding lectin (MBL) has been proposed as one of these factors. We therefore investigated the influence of MBL2 gene variants on disease severity, age at acquisition of Pseudomonas aeruginosa, and survival in CF patients. Methods MBL2 variants were studied in 106 Argentinean pediatric CF patients carrying two severe CFTR mutations. Clinical phenotype was defined according to the Shwachman score and lung function tests. Age at infection with P. aeruginosa and age at death were also recorded. Results MBL insufficiency was associated with a 3.5-fold risk of having a severe phenotype (CI 95%: 1.2–10.3, p = 0.03). It was also associated with an earlier onset of infection with P. aeruginosa (p = 0.035). No statistically significant differences were found in FEV1 and survival. Conclusions MBL insufficiency was associated with detrimental progression of the disease. These results together with previous findings suggest that the effect of MBL2 expression may be a major determinant of the severity of the clinical phenotype in patients with CF.
    Journal of Cystic Fibrosis 01/2015; 14(1):78-83. DOI:10.1016/j.jcf.2014.07.012 · 3.82 Impact Factor
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    • "It has been shown that heterozygous genotypes have less stable MBL oligomers (Larsen et al., 2004), which could result in an increased degradation of the protein (Matsushita et al., 1995; Naito et al., 1999). It has also been shown that less oligomerized MBL binds poorly to mannan and would therefore be less likely to be detected in the functional assays, which are mostly used to measure MBL levels (Garred et al., 2003b) and is less able to activate the LP (Larsen et al., 2004). In this review MBL-deficiency is defined by the measurement of functional binding of MBL to the ligand, unless otherwise stated. "
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    ABSTRACT: 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.
    Molecular Immunology 10/2014; 61(2). DOI:10.1016/j.molimm.2014.06.005 · 3.00 Impact Factor
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    • "Human mannose binding lectin (MBL) is a C-type (Ca 2 + dependent ) mammalian lectin of the innate immune system, coded by the MBL2 gene and specifically synthesized in the liver in two forms, serum MBL (S-MBL) and intracellular MBL (I-MBL), encoded by a single mRNA (Garred, 2003; Kilpatrick, 2002; Ma, 1997; Turner, 2003). Both forms exist as homo-oligomers of 32 kDa units and three subunits form a " structural unit " (Kurata, 1994). "
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    ABSTRACT: Human immunodeficiency virus -1 (HIV-1) enters the brain early during infection and leads to severe neuronal damage and central nervous system impairment. HIV-1 envelope glycoprotein 120 (gp120), a neurotoxin, undergoes intracellular trafficking and transport across neurons; however mechanisms of gp120 trafficking in neurons are unclear. Our results show that mannose binding lectin (MBL) that binds to the N-linked mannose residues on gp120, participates in intravesicular packaging of gp120 in neuronal subcellular organelles and also in subcellular trafficking of these vesicles in neuronal cells. Perinuclear MBL:gp120 vesicular complexes were observed and MBL facilitated the subcellular trafficking of gp120 via the endoplasmic reticulum (ER) and Golgi vesicles. The functional carbohydrate recognition domain of MBL was required for perinuclear organization, distribution and subcellular trafficking of MBL:gp120 vesicular complexes. Nocodazole, an agent that depolymerizes the microtubule network, abolished the trafficking of MBL:gp120 vesicles, suggesting that these vesicular complexes were transported along the microtubule network. Live cell imaging confirmed the association of the MBL:gp120 complexes with dynamic subcellular vesicles that underwent trafficking in neuronal soma and along the neurites. Thus, our findings suggest that intracellular MBL mediates subcellular trafficking and transport of viral glycoproteins in a microtubule-dependent mechanism in the neurons.
    Neurobiology of Disease 09/2014; 69. DOI:10.1016/j.nbd.2014.05.002 · 5.20 Impact Factor
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