Mannan-binding Protein Research Articles

Establishment of a Multiplex Detection Method for Common Bacteria in Blood Based on Human Mannan-Binding Lectin Protein-Conjugated Magnetic Bead Enrichment Combined with Recombinase-Aided PCR Technology

ObjectiveRecombinase-aided polymerase chain reaction (RAP) is a sensitive, single-tube, two-stage nucleic acid amplification method. This study aimed to develop an assay that can be used for the early diagnosis of three types of bacteremia caused by Staphylococcus aureus (SA), Pseudomonas aeruginosa (PA), and Acinetobacter baumannii (AB) in the bloodstream based on recombinant human mannan-binding lectin protein (M1 protein)-conjugated magnetic bead (M1 bead) enrichment of pathogens combined with RAP. MethodsRecombinant plasmids were used to evaluate the assay sensitivity. Common blood influenza bacteria were used for the specific detection. Simulated and clinical plasma samples were enriched with M1 beads and then subjected to multiple recombinase-aided PCR (M-RAP) and quantitative PCR (qPCR) assays. Kappa analysis was used to evaluate the consistency between the two assays. ResultsThe M-RAP method had sensitivity rates of 1, 10, and 1 copies/μL for the detection of SA, PA, and AB plasmids, respectively, without cross-reaction to other bacterial species. The M-RAP assay obtained results for < 10 CFU/mL pathogens in the blood within 4 h, with higher sensitivity than qPCR. M-RAP and qPCR for SA, PA, and AB yielded Kappa values of 0.839, 0.815, and 0.856, respectively (P < 0.05). ConclusionAn M-RAP assay for SA, PA, and AB in blood samples utilizing M1 bead enrichment has been developed and can be potentially used for the early detection of bacteremia.

Adding MASP1 to the lectin pathway-Leprosy association puzzle: Hints from gene polymorphisms and protein levels.

Deposition of complement factors on Mycobacterium leprae may enhance phagocytosis. Such deposition may occur through the lectin pathway of complement. Three proteins of the lectin pathway are produced from the gene MASP1: Mannan-binding lectin-associated serine protease 1 (MASP-1) and MASP-3 and mannan-binding lectin-associated protein of 44 kDa (MAp44). Despite their obvious importance, the roles played by these proteins have never been investigated in leprosy disease. We haplotyped five MASP1 polymorphisms by multiplex sequence-specific PCR (intronic rs7609662*G>A and rs13064994*C>T, exon 12 3'-untranslated rs72549262*C>G, rs1109452*C>T and rs850314*G>A) and measured MASP-1, MASP-3 and MAp44 serum levels in 196 leprosy patients (60%, lepromatous) and 193 controls. Lower MASP-3 and MAp44 levels were observed in patients, compared with controls (P = 0.0002 and P<0.0001, respectively) and in lepromatous, compared with non-lepromatous patients (P = 0.008 and P = 0.002, respectively). Higher MASP-3 levels were present in controls carrying variants/haplotypes associated with leprosy resistance (rs13064994*T, rs1109452_rs850314*CG within GT_CCG and rs850314*A: OR = 0.5-0.6, Pcorr = 0.01-0.04). Controls with rs1109452*T, included in susceptibility haplotypes (GT_GTG/GT_CTG: OR = 2.0, Pcorr = 0.03), had higher MASP-1 and lower MASP-3 levels (P≤0.009). Those with GC_CCG, presented increasing susceptibility (OR = 1.7, Pcorr = 0.006) and higher MAp44 levels (P = 0.015). MASP-3 expression decreased in patients, compared with controls carrying rs1109452_rs850314*CA or CG (P≤0.02), which may rely on exon 12 CpG methylation and/or miR-2861/miR-3181 mRNA binding. Polymorphisms regulating MASP-3/MAp44 availability in serum modulate leprosy susceptibility, underlining the importance of lectin pathway regulation against pathogens that exploit phagocytosis to parasitize host macrophages.

Plasma levels of MASP-1, MASP-3 and MAp44 in patients with type 2 diabetes: influence of glycaemic control, body composition and polymorphisms in the MASP1 gene.

Mounting evidence indicates that adverse activation of the complement system plays a role in the development of diabetic vascular complications. Plasma levels of the complement proteins mannan-binding lectin (MBL) and its associated serine proteases (MASP-1 and MASP-2) are elevated in diabetes. We hypothesized that single nucleotide polymorphisms (SNPs) in the MASP1 gene may contribute to altered plasma levels of the belonging gene products; MASP-1, MASP-3 and mannan-binding lectin-associated protein of 44 kDa (MAp44) in patients with type 2 diabetes. To investigate this, we compared plasma levels of MASP-1, MASP-3 and MAp44 in 100 patients with type 2 diabetes and 100 sex- and age-matched controls. Ten carefully selected SNPs were analysed using TaqMan® genotyping assay. Additionally, we included a streptozotocin-induced diabetes mouse model to directly examine the effect of inducing diabetes on MASP-1 levels. MASP-1 levels were significantly higher among patients with type 2 diabetes compared with healthy controls (P = 0·017). Five SNPs (rs874603, rs72549254, rs3774275, rs67143992, rs850312) in the MASP1 gene were associated with plasma levels of MASP-1, MASP-3 and MAp44. In the diabetes mouse model, diabetic mice had significantly higher MASP-1 levels than control mice (P = 0·003). In conclusion, MASP-1 levels were higher among patients with type 2 diabetes and diabetic mice. The mechanism behind this increase remains elusive.

Substrate adaptabilities of Thermotogae mannan binding proteins as a function of their evolutionary histories.

The Thermotogae possess a large number of ATP-binding cassette (ABC) transporters, including two mannan binding proteins, ManD and CelE (previously called ManE). We show that a gene encoding an ancestor of these was acquired by the Thermotogae from the archaea followed by gene duplication. To address the functional evolution of these proteins as a consequence of their evolutionary histories, we measured the binding affinities of ManD and CelE orthologs from representative Thermotogae. Both proteins bind cellobiose, cellotriose, cellotetraose, β-1,4-mannotriose, and β-1,4-mannotetraose. The CelE orthologs additionally bind β-1,4-mannobiose, laminaribiose, laminaritriose and sophorose while the ManD orthologs additionally only weakly bind β-1,4-mannobiose. The CelE orthologs have higher unfolding temperatures than the ManD orthologs. An examination of codon sites under positive selection revealed that many of these encode residues located near or in the binding site, suggesting that the proteins experienced selective pressures in regions that might have changed their functions. The gene arrangement, phylogeny, binding properties, and putative regulatory networks suggest that the ancestral mannan binding protein was a CelE ortholog which gave rise to the ManD orthologs. This study provides a window on how one class of proteins adapted to new functions and temperatures to fit the physiologies of their new hosts.

Mannan-Binding Protein, a C-Type Serum Lectin, Recognizes Primary Colorectal Carcinomas through Tumor-Associated Lewis Glycans

Mannan (mannose)-binding protein (MBP) is a C-type serum lectin that plays a key role in innate immunity. MBP forms large multimers (200-600 kDa) and exhibits broad specificity for mannose, N-acetylglucosamine, and fucose. MBP exhibits high affinity for unique oligosaccharides that have been isolated from human colorectal carcinoma (SW1116) cells and characterized as highly fucosylated high m.w. type 1 Lewis glycans. In this study, we first demonstrated that MBP recognizes human primary colorectal carcinoma tissues through tumor-associated MBP ligands. We performed fluorescence-based histochemistry of MBP in human colorectal carcinoma tissues and showed that MBP clearly stained cancer mucosae in a Ca(2+)-dependent manner. Coincubation with plant (Aleuria aurantia) lectin, but not Con A, blocked MBP staining, indicating that fucose, rather than mannose, is involved in this interaction. The expression of MBP ligands was detected in 127 of 330 patients (38.5%), whereas, most significantly, there was no expression in 69 nonmalignant tissues. The MBP-staining pattern in cancer mucosae significantly overlapped with that of Lewis b [Fucα1-2Galβ1-3(Fucα1-4)GlcNAc] staining, but the Lewis b staining in normal tissues was not associated with MBP staining. In addition, the MBP staining correlated inversely with the expression of CA19-9 Ag, and MBP stained 11 of 25 (44%) CA19-9 (sialyl Lewis a [NeuAc(α2-3)Galβ1-3(Fucα1-4)GlcNAc])(-) colorectal carcinoma tissues. We found a favorable prognosis in patients with MBP ligand(+) tumors. These results suggest that selective recognition of cancer cells by endogenous MBP seems to be associated with an antitumor effect and that tissue staining with MBP in combination with CA19-9 may serve as a novel indicator of colorectal carcinoma tissues.

Functional assay using lectin gene targeting technologies (over-expression).

Function of lectin depends on its amino acid sequence of carbohydrate-recognition domain (CRD), conformation, and extracellular/intracellular localization. Altering lectin gene expression by over-expression or knockdown is a powerful tool for analyzing its cellular function. Here, we describe a method of lectin gene over-expression, taking a C-type lectin, mannan-binding protein (MBP), as an example. Carbohydrate-binding ability of MBP, its subcellular localization, and functional co-localization with ligand glycoprotein are assayed comparing with an inactive mutant MBP.

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.

Affinity chromatographic purification of human immunoglobulin M from human B lymphocyte cell culture supernatant

Compared to immunoglobulin G purification with extensively studied affinity ligands such as protein A and protein G, little work has been done on affinity chromatographic purification of immunoglobulin M. Hexamer peptide ligand HWRGWV, previously shown to bind specifically to the Fc fragment of IgG, also demonstrated potential for IgM purification. This study presents further characterization and investigation of this ligand for its potential for purification of IgM. Different running conditions were employed in order to improve the recovery and purity of IgM. The final recovery and purity of the antibody is feedstock dependent, but can reach levels of both recovery and purity as high as 95%. The dependence of the recovery and purity on total loading amount and initial IgM concentration were investigated and discussed. Although relatively low dynamic binding capacities (DBC) in the range of 4.6–13.1mg IgM/mL resin at linear flow rates from 173 to 35cm/h were obtained for IgM compared to IgG because of the large molecular weight of IgM, the DBC value of HWRGWV for IgM is much greater than protein-based IgM affinity ligands found in the literature and is competitive with current commercially available affinity ligands, such as KAPTIVE-M, CaptureSelect IgM and Ultralink Immobilized Mannan Binding Protein.

Growth Hormone Abuse and Biological Passport: Is Mannan-Binding Lectin a Complementary Candidate?

In the detection of human growth hormone (GH) abuse, the approach based on altered GH-related biomarkers is also being considered with respect to its application within the context of a biological passport. As a potential biomarker, mannan-binding lectin (MBL), which is reported to respond to recombinant GH (rGH) administration, is evaluated here. Randomized and single blind and approved by the Ethical Committee (Comité Ético de Investigación Clínica-Instituto Municipal de Asistencia Sanitaria). One group of 12 male subjects (24.2 ± 2.2 years; 76.1 ± 6.1 kg) was studied. Mannan-binding lectin concentration was measured in 12 healthy individuals after subcutaneous daily doses of 6 IU of rGH administration. Mannan-binding lectin serum concentration increased after rGH administration. Mannan-binding lectin concentration increases were observed 48 hours after the first administration and remained elevated for several days after the final dose. Mannan-binding lectin concentration increase and elapsed time to recover initial MBL values after the last rGH administration. Absolute values displayed high interindividual variability, and 1 individual did not show any MBL increase (potential MBL deficiency). Mannan-binding lectin protein showed a clear concentration increase after continued rGH administration, despite the high heterogeneity found between individuals. The use of MBL as a complementary GH-related biomarker could be of interest, taking advantage of the high increases (up to 700%) and the relatively slow recovery time.

Role of interaction of mannan-binding protein with meprins at the initial step of complement activation in ischemia/reperfusion injury to mouse kidney

Ischemia/reperfusion (I/R) is an important cause of acute renal failure. Recent studies have shown that the complement system mediated by the mannan-binding protein (MBP), which is a C-type serum lectin recognizing mannose, fucose and N-acetylglucosamine residues, plays a critical role in the pathogenesis of ischemic acute renal failure. MBP causes complement activation through the MBP lectin pathway and a resulting complement component, C3b, is accumulated on the brush borders of kidney proximal tubules in a renal I/R-operated mouse kidney. However, the initial step of the complement activation has not been studied extensively. We previously identified both meprins α and β, highly glycosylated zinc metalloproteases, localized on kidney proximal tubules as endogenous MBP ligands. In the present study, we demonstrated that serum-type MBP (S-MBP) and C3b were co-localized with meprins on both the cortex and the medulla in the renal I/R-operated mouse kidney. S-MBP was indicated to interact with meprins in vivo in the I/R-operated mouse kidney and was shown to initiate the complement activation through the interaction with meprins in vitro. Taken together, the present study strongly suggested that the binding of S-MBP to meprins triggers the complement activation through the lectin pathway and may cause the acute renal failure due to I/R on kidney transplantation and hemorrhagic shock.

The carbohydrate recognition domain of collectins

Collectins are effector molecules of the innate immune system that play an important role in the first line of defence against bacteria, viruses and fungi. Most of their interactions with microorganisms are mediated through their carbohydrate recognition domain (CRD), which binds in a Ca(2+)-dependent manner to glycoconjugates. This domain is a well-known structure that is present in a larger group of proteins comprising the C-type lectin domain family. Collectins form a subgroup within this family based on the presence of a collagen domain and the trimerization of CRDs, which are essential for the ligand-binding properties of these proteins. The ligand specificity among the nine collectin members is significantly different as a result of both the structural organization of the trimers and specific sequence changes in the binding pocket of the CRD. In addition, some collectin members have additional features, such as N-linked glycosylation of CRD residues and additional loop structures within the CRD that have a large impact on their interaction with the glycoconjugates present on microorganisms or host cells. The availability of crystal structures of three members of the collectin family (surfactant proteins A and D and mannan-binding protein) provides an important tool for addressing the impact of these CRD differences on ligand binding. In this review, the structural differences and similarities between the CRDs of collectins are summarized and their relationship with their ligand-binding characteristics is discussed.

Single nucleotide polymorphisms in collagenous lectins and other innate immune genes in pigs with common infectious diseases

Innate immune recognition of pathogens involves various surface receptors and soluble proteins that precede agglutination, complement activation, phagocytosis, and the adaptive immune response. Mannan-binding lectins (MBLs), ficolins (FCNs) and surfactant protein A (SP-A) are soluble collagenous lectins that bind surface structures of various bacteria, viruses and fungi. Some single nucleotide polymorphisms (SNPs) in collagenous lectin genes of humans and other species, including pigs, have been implicated in variation in susceptibility to infectious and inflammatory diseases. In this study we determined the frequencies of 13 SNP alleles of MBL-A, MBL-C, ficolin-α, ficolin-β, and SP-A in 1324 healthy pigs and 461 pigs diagnosed with common infectious diseases at necropsy. For comparison, we also analyzed 12 other SNP alleles in several other innate immune genes, including galectins and TLRs. Several SNPs within genes encoding porcine MBL-A, MBL-C and SP-A were more frequent in pigs diagnosed at necropsy with various diseases or pathogens. These findings suggest that several collagenous lectin SNPs are associated with disease susceptibility and therefore might be genetic markers of impaired innate immune function.

Recognition of Endogenous Ligands by C-Type Lectins:Interaction of Serum Mannan-binding Protein with Tumor-associated Oligosaccharide Epitopes

動物レクチンはヒトや動物に含まれる糖鎖の生理的役割の解明に大きく貢献してきた。マンナン結合タンパク質（MBP）は、その糖鎖認識ドメイン(CRD) に存在する糖結合部位を介してマンノース、N-アセチルグルコサミン、L-フコースに結合する。病原微生物では、細胞表層のマンノオリゴ糖がMBPに結合する主要な糖鎖である。これに対し、内在性の標的であるヒト結腸癌細胞株SW1116の場合、I型のルイス型オリゴ糖鎖がMBPの主要な結合相手となる。すなわち、SW1116細胞の可溶化物オリゴ糖鎖をMBPカラムにかけると、4個以上のFuc(Hex-HexNAc)ユニットをもつ複合型糖鎖(MLO)がカラムに結合するのに対して、3個以下のFuc(Hex-HexNAc)ユニットを持つ複合型糖鎖および高マンース型糖鎖 (Man5 to Man8)はMBPカラムに結合しない。これらの結果は、MLOがこれまで報告のない新規な癌関連糖鎖であることを示している。なぜMLOがこのように高い親和性を示すのか、今後の研究課題であるが、コンピュータモデリングによるとMBPの3量体と Leb-(Lea)x4-Lex糖鎖の間に興味深い複合体の形成が可能なことが示されている。

First report on the isolation of immunoglobulin M of guppy, Poecilia reticulata, for the production of polyclonal antibodies

As guppies are one of the commercially important fish in freshwater ornamental aquaculture industry, it is important to gain an understanding of guppy immune response for infectious disease control. Till now, the number of study that examined the immune response of guppies is limited and effective tools for monitoring guppy antibody have not been reported. In this study, we successfully isolated guppy IgM using mannan-binding protein (MBP) affinity chromatography and produced specific polyclonal antibodies against guppy IgM heavy and light chains, that showed a molecular weight of approximately 74 and 23kDa respectively. The produced polyclonal antibodies were used to develop an enzyme-linked immunosorbent assay (ELISA) and have demonstrated to be an effective tool for the detection and quantification of antigen-specific antibody of guppies immunized with Pseudomonas fluorescens. In conclusion, the produced anti-guppy IgM polyclonal antibodies should prove its future implications for immunology and epidemiology studies in guppies.

Characterization of the interaction between serum mannan-binding protein and nucleic acid ligands

Serum MBP, also known as MBL, is a C-type lectin that is known to be a soluble host defense factor involved in innate immunity. It has been well established that dying microbes and apoptotic cells release highly viscous DNA that induces inflammation and septic shock, and apoptotic cells display fragmented DNA on their surfaces. However, PRRs that mediate the recognition and clearance of free DNA and fragmented DNA in apoptotic cells have not been characterized clearly. Although MBP was reported recently to bind DNA as a novel ligand, binding characterization and the recognition implications have not been addressed yet. In this study, we show that MBP can bind DNA and RNA in a calcium-dependent manner from a variety of origins, including bacteria, plasmids, synthetic oligonucleotides, and fragmented DNA of apoptotic cells. Direct binding and competition studies indicate that MBP binds nucleic acids via its CRD to varying degrees and that MBP binds dsDNA more effectively than ssDNA and ssRNA. Furthermore, we reveal that the MBP-DNA complex does not trigger complement activation via the MBP lectin pathway, and the lectin pathway of complement activation is required for MBP-mediated enhancement of phagocytosis of targets bearing MBP ligands and that MBP can recognize the fragmented DNA presented on apoptotic cells. Therefore, we propose that the MBP lectin pathway may support effective recognition and clearance of cellular debris by facilitating phagocytosis, possibly through immunomodulatory mechanisms, thus preventing autoimmunity.

Isolation of murine and human immunoglobulin m and murine immunoglobulin D.

This unit describes two classical protocols for the purification of IgM-dialysis of ascites fluid, tissue culture medium, or bioreactor supernatants against distilled water to precipitate pure IgM, and ammonium sulfate precipitation. Both protocols can be followed by size-exclusion chromatography to obtain a highly purified product. Recently, an affinity method for purification of IgM has been developed using mannan-binding protein, and is described here. The third approach presented is a one-step IgD purification method, designed specifically for murine derived samples, that uses Sepharose coupled to lectin derived from the seeds of Griffonia simplicifolia-1. This represents a simple, rapid, and gentle, approach to isolating this highly labile immunoglobulin from IgD-containing ascites or hybridoma sources.

재조합 mannose-binding lectin 단백질과 anti-mannose-binding lectin polyclonal 항체 제작

선천성 면역은 숙주의 물리적 방어벽을 뚫고 침입하는 감염성 질병 원인균에 대항하는 첫 번째 방어로서 아주 중요한 역할을 한다. Mannose-binding lectin (MBL 또는 mannan-binding protein, MBP)은 혈청 내에 존재하는 면역성 단백질로서 감염 후 즉시 유발되는 acute phase response의 특정 단백질이다. MBL 단백질은 세균, 바이러스, 곰팡이, 기생충 등의 탄수화합물 구조에 결합하여 식균 작용을 돕거나 보체경로를 활성화 시킨다. MBL 단백질은 C-말단이 탄수화물을 인식하는 도메인이며, 연결 목 부위와 콜라겐 부위로 구성되어 있다. 혈청 내의 MBL 농도가 낮으면 높은 빈도로 면역결핍현상이 관찰된다고 알려져 있다. MBL 단백질의 기능과 유전에 대해 많은 연구가 되어져 왔으나 아직 MBL 단백질 복합체 등에 대한 연구는 많이 이루어져 있지 않다. 따라서 MBL 연구에 필수적인 MBL cDNA 제조와 재조합 단백질의 합성, 그리고 재조합 단백질을 항원으로 사용하여 polyclonal antibody를 생산한 연구 결과를 보고하는 바이다. 본 연구결과로 획득한 MBL cDNA, 재조합 단백질과 anti-MBL 항체는 앞으로의 MBL 연구에 절대적으로 필요한 도구가 될 것으로 생각된다. The innate immune system is important for the first line of host defence against infectious agents, which have penetrated the mechanical barriers. Mannose-binding lectin (MBL or mannan-binding protein, MBP) is a serum protein that is synthesized in the liver as a part of the acute phase response. MBL binds to carbohydrate structures presented by a wide range of pathogenic bacteria, viruses, fungi, and parasites. MBL is synthesized as a monomer that has a carboxy-terminal carbohydrate recognition domain, a neck region and a collagen region. Low MBL level was reported to be the most frequent immuno-deficiency syndrome. Although extensive studies have yielded detailed information on the structure of MBL, functions of the MBL complex are not fully understood yet. We, here, present cloning process of MBL cDNA from the rat liver and production of truncated recombinant MBL protein using a bacterial expression system in order to produce anti-MBL polyclonal antibody. Anti-MBL polyclonal antibody was raised in a New Zealand rabbit and its affinity was tested against recombinant protein using western blot technique. MBL cDNA, recombinant protein and anti-MBL antibody could be used as great arsenals to dissect cellular biochemistry of MBL.

Highly fucosylated N-glycan ligands for mannan-binding protein expressed specifically on CD26 (DPPVI) isolated from a human colorectal carcinoma cell line, SW1116

The serum mannan-binding protein (MBP) is a host defense C-type lectin specific for mannose, N-acetylglucosamine, and fucose residues, and exhibits growth inhibitory activity toward human colorectal carcinoma cells. The MBP-ligand oligosaccharides (MLO) isolated from a human colorectal carcinoma cell line, SW1116, are large, multiantennary N-glycans with highly fucosylated polylactosamine-type structures having Le(b)-Le(a) or tandem repeats of the Le(a) structure at their nonreducing ends. In this study, we isolated the major MBP-ligand glycoproteins from SW1116 cell lysates with an MBP column and identified them as CD26/dipeptidyl peptidase IV (DPPIV) (110 kDa) and CD98 heavy chain (CD98hc)/4F2hc (82 kDa). Glycosidase digestion revealed that CD26 contained such complex-type N-glycans that appear to mediate the MBP binding. MALDI-MS of the N-glycans released from CD26 by PNGase F demonstrated conclusively that CD26 is the major MLO-carrying protein. More interestingly, a comparison of the N-glycans released from the MBP-binding and non-MBP-binding glycopeptides suggested that complex-type N-glycans carrying a minimum of 4 Le(a)/Le(b) epitopes arranged either as multimeric tandem repeats or terminal epitopes on multiantennary structures are critically important for the high affinity binding to MBP. Analysis of the N-glycan attachment sites demonstrated that the high affinity MLO was expressed preferentially at some N-glycosylation sites, but this site preference was not so stringent. Finally, hypothetical 3D models of tandem repeats of the Le(a) epitope and the MBP-Lewis oligosaccharide complex were presented.

The level of the serum opsonin, mannan-binding protein in HIV-1 antibody-positive patients.

The concentrations of mannan-binding protein (MBP) in consecutive samples from 10 HIV+ persons were estimated using an ELISA based on polyclonal rabbit anti-MBP. The changes in MBP with time were similar in HIV+ and HIV- persons, and did not appear to be of clinical significance. MBP was determined in a further 70 persons found HIV-1+ during a period of 2.5 years (1984-1986). Out of the total of 80 patients, 32 have by now died from AIDS. According to the serum level of MBP the HIV-infected persons were grouped into high (> 650 ng MBP/ml), intermediate (101-650 ng/ml), and low MBP (< 101 ng/ml). At the termination of the study the frequency of deaths/total in each of the groups were: high MBP, 14/39 (36%); intermediate MBP, 12/26 (46%); and low MBP, 6/14 (43%). There was no association between the MBP level of the individual and the progressive loss of CD4+ T cells, and the level of MBP was not predictive for the length of time between the detection of HIV antibodies and development of AIDS, nor for the duration of AIDS before death occurred. The number of HIV+ persons without detectable MBP (10%) was significantly higher than previously reported for healthy persons (2.4%, P = 0.027). The course of HIV infection does not seem to be influenced by the level of MBP, nor does the antimicrobial activity of MBP appear to affect the progression of AIDS. Further studies are required to substantiate the significance of absence of MBP in the susceptibility to HIV.

Gene frequency and partial protein characterization of an allelic variant of mannan binding protein associated with low serum concentrations.

Low plasma concentration of mannan binding protein (MBP) has been shown to be the basis for a common opsonic deficiency and suggested to be caused by a single nucleotide substitution at base 230 of exon 1 in the MBP gene. This substitution causes a replacement of glycine (codon GGC) with aspartic acid (codon GAC). Of 123 healthy Danish individuals investigated by polymerase chain reaction performed on exon 1, followed by restriction fragment length polymorphism or allospecific probing, 93 were homozygous (75.6%) for GGC, 28 heterozygous (22.8%), and two homozygous for GAC (1.6%). The gene frequency of the GAC allele was found to be 0.13. DNA sequencing of the cloned exon 1 from one GAC homozygous individual revealed no other substitution. The median MBP concentration in the group containing the GAC allele was 6.4 times lower than in the GGC homozygous group (195 and 1234 micrograms/l respectively). However, the range in plasma concentrations of MBP was wide and overlapping between the groups. MBP protein was detected in both the GAC homozygotes (9 and 387 micrograms/l). Furthermore, no difference in relative mass and biological activity (mannan binding) was found when sera containing the two forms of MBP were investigated. Accordingly, it can be concluded that the GAC allele is able to produce a functional MBP protein which may be detected in serum at low concentrations.