The 'involution' of mannose-binding lectin

Mannose-binding lectin (MBL) acts as a serum opsonin in innate immune defense and induces complement activation by the lectin pathway. In humans, low levels of functional serum MBL are caused by the dominant action of three single nucleotide substitutions in exon 1 that disrupt the glycine-rich backbone structure of the protein. The presence of common MBL variant alleles is associated with both infectious and autoimmune diseases. Conversely, it has also been suggested that MBL variants are maintained because of selective advantages for the host. In man, the MBL genetic system comprises one functional gene (MBL2) and one expressed pseudogene (MBL1P1), whereas the lower primate, the rhesus monkey resembles rodents with two functional MBL genes. We have investigated the molecular mechanisms behind the evolutionary loss of MBL expression from lower primates to man, including silencing of the MBL1P1 gene and the generation of MBL2 variant structural alleles and promoter polymorphisms leading to the present human MBL2 haplotypes. We present data showing that the MBL1P1 gene has been repeatedly hit throughout evolution and silenced eventually by mutations in the glycine residues of the collagen-like region. Our results indicate that the MBL1P1 gene has been selectively turned off during evolution through the same molecular mechanisms causing the MBL2 variant alleles in man, suggesting an evolutionary selection for low-producing MBL genes.     

Autoantibodies against mannose-binding lectin in systemic lupus erythematosus

In systemic lupus erythematosus (SLE), autoantibodies directed against complement components of the classical pathway, especially against C1q, are associated with severe disease and are of prognostic value for flares of lupus nephritis. Mannose-binding lectin (MBL), the recognition unit of the MBL pathway of complement activation, has structural similarities to C1q. Deficiencies of MBL have been shown to predispose to the development of SLE and to influence the course of the disease. We hypothesized that the presence of autoantibodies to MBL, analogous to autoantibodies to C1q in patients with SLE, may contribute to disease development. The occurrence of anti-MBL autoantibodies was assessed by enzyme-linked immunosorbent assay (ELISA) of 68 serum samples from 20 patients with SLE and in serum from 70 healthy controls. Levels of antibodies directed against MBL were significantly higher in patients with SLE compared to healthy subjects. No significant difference was found between patients with active disease compared to those with inactive disease. While the occurrence of anti-C1q autoantibodies was associated with renal involvement, no such relationship was found for anti-MBL autoantibodies. A significant correlation was found between anti-MBL and anti-C1q antibody levels. The level of anti-MBL antibodies was negatively correlated with MBL-complex activity of circulating MBL. Anti-MBL autoantibodies were of the immunoglobulin G (IgG) isotype and the binding site of IgG anti-MBL was located in the F(ab')2 portion. We conclude that anti-MBL are present in sera from SLE patients and influence the functional activity of MBL.     

The development of asthma in children infected with Chlamydia pneumoniae is dependent on the modifying effect of mannose-binding lectin

BACKGROUND: Although several studies found associations between infection with Chlamydia pneumoniae and asthma, these were mainly restricted to the exacerbation of the symptoms in adults with known asthma. Data about the role of C pneumoniae in the initiation and development of asthma in children are controversial. OBJECTIVE: We investigated the role of C pneumoniae infection in 139 children with asthma, comparing them with 174 healthy control subjects. Furthermore, we studied the modifying effect of mannose-binding lectin (MBL) variant alleles on the susceptibility to asthma in children infected with C pneumoniae. METHODS: C pneumoniae-specific antibodies were measured by means of ELISA, and MBL genotypes were determined by means of PCR-RFLP. RESULTS: There were no significant differences in the percentage of children with positive results for C pneumoniae-specific antibodies between patients and control subjects. Among asthmatic children carrying variant MBL alleles, there were significantly more patients with positive results for C pneumoniae-specific IgG than among control children with variant MBL genotypes (63.7% vs 40.7% of asthmatic vs control children, respectively; odds ratio adjusted for age and sex, 2.21; 95% CI, 1.10-4.41; P =.02). Infected children with variant MBL alleles were found to have a higher risk of asthma development than infected children with normal MBL genotype. This risk was especially high in children with chronic or recurrent infection (positive results for both IgA and IgG; adjusted odds ratio, 5.38; 95% CI, 1.75-14.36; P =.01), but no increased risk was seen in children with current C pneumoniae infection (positive results for IgM). CONCLUSION: This study indicates the important role of variant MBL alleles in the susceptibility to asthma in children infected with C pneumoniae.     

The association between mannose-binding lectin gene polymorphism and rheumatic heart disease

Mannan-binding lectin (MBL) is an innate pattern recognition molecule known to play a key role in pathogen clearance. As MBL2 gene polymorphism is associated to an increased susceptibility to infection, we aimed to determine genetic variations in the MBL2 gene in rheumatic heart disease (RHD). Genetic variations in the promoter and exon 1 region of the MBL2 gene were analyzed in 107 patients with RHD and 105 controls by real-time polymerase chain reaction. The frequency of MBL2* A/A genotype was significantly higher in RHD patients (71/107, 66.36% vs 52/105, 49.52%, p ≤ 0.02, OR = 1.99, 95% CI, 1.15–3.50). A/A genotypes were associated with higher levels of MBL in RHD compared with controls with the same genotype (p ≤ 0.004). The frequency of HYPA/HYPA, HYPA/LYQA, and LYQA/LYQA haplotypes was also increased in RHD (p ≤ 0.03, OR = 1.98, 95% CI, 1.05–3.73). However, the frequency of MBL2 variant alleles (termed “O”) was lower among patients (39/214, 18.2% vs 63/210, 30.0%, p ≤ 0.006, OR = 0.52, 95% CI, 0.33–0.82), which was also seen for O/O genotypes (3/107, 2.8% vs 10/105, 9.5%, p ≤ 0.05, OR = 0.27, 95% CI, 0.07–1.03). This data suggests a role for MBL genotypes in the susceptibility to RHD. However, it still remains unclear whether A/A homozygosity is a risk factor for RHD or rheumatic fever itself.     

Significantly increased levels of mannose-binding lectin (MBL) in rheumatic heart disease: a beneficial role for MBL deficiency

Although mannose-binding lectin (MBL) is known to be involved in the primary defense against microorganisms, there are emerging lines of evidence for an active proinflammatory role for MBL in different chronic diseases. In this study we determined the circulating levels of MBL in patients with rheumatic heart disease (RHD). A total of 100 patients (77 women, 23 men; mean age 45.8 +/- 11 years, range 19-76 years) with chronic RHD, and a previous diagnosis of rheumatic fever, were studied. Transthoracic echocardiography was performed in all patients to evaluate valvular heart disease. Ninety-nine healthy individuals matched for age, sex and ethnic origin were included as controls. MBL concentration was measured by enzyme-linked immunosorbent assay and C3 and C4 levels by turbidimetry. MBL levels were significantly higher in patients with RHD than in healthy subjects (mean +/- SEM: 3036.2 +/- 298.9 ng/ml versus 1942.6 +/- 185.5 ng/ml, P <0.003). In addition, MBL deficiency was more prevalent in controls (17.1%) than in patients (9% P <0.09). Concentrations of C4 were within the normal range (22.7 +/- 0.8 mg/dl, normal: 10.0-40.0 mg/dl), while C3 concentrations were found to be elevated (109.2 +/- 3.6 mg/dl, normal: 50.0-90.0 mg/dl). No correlation was observed between serum MBL levels and valve area or the type of surgical procedure. The significantly elevated circulating MBL levels in patients with RHD together with the greater prevalence of MBL deficiency in controls suggest that MBL may cause undesirable complement activation contributing to the pathogenesis of RHD.     

Heterozygosity of mannose-binding lectin (MBL2) genotypes predicts advantage (heterosis) in relation to fatal outcome in intensive care patients

Polymorphisms in the MBL2 gene, which affect the structure and influence on the serum concentration of mannose-binding lectin (MBL), are associated with inflammatory and infectious conditions. The importance of MBL2 polymorphisms on outcome in critical ill patients is unclear. Five hundred and thirty-two consecutive critically ill patients admitted to an intensive care unit (ICU) were included over a period of 18 months. Five hundred and thirty-three individuals served as controls. Vital status was obtained 15.5 months after the last patient was included. MBL2 polymorphisms were determined by a PCR-based assay. Homozygosity for MBL2 variant alleles (O/O) causing MBL structural defects was associated with the highest adjusted mortality rate followed by homozygosity for the normal MBL2 allele (A/A) encoding high MBL levels, whereas heterozygous A/O patients had the most favourable outcome (P = 0.015). MBL2 alleles were not associated with death in ICU (n = 166, P = 0.7), but the association appeared soon after discharge from ICU (n = 366): hazard ratio (HR) for O/O using A/A as reference was 1.33 (95% CI: 0.8-2.2) and for A/O it was 0.62 (95% CI: 0.4-0.8) respectively (P = 0.0045) at completion. No difference in MBL2 frequency was observed between patients and controls at baseline, and between patients classified as having sepsis or not. However, patients with the MBL2 O/O genotype had an increased frequency of Gram-positive bacterial infection (P = 0.01). Heterozygosity for MBL2 alleles confers a protective effect whereas homozygosity is associated with the worst outcome soon after discharge from ICU. This may be an example of heterosis.     

Association of mannose-binding lectin gene (MBL2) polymorphisms with rheumatoid arthritis in an Indian cohort of case-control samples

Single nucleotide polymorphisms in the mannose-binding lectin (MBL2) gene, as well as the serum MBL2 level, have been associated with various autoimmune diseases. We investigated whether such polymorphisms and/or the serum MBL2 level were associated with rheumatoid arthritis (RA) in an Indian population. The frequency of the B variant (codon 54) of the MBL2 gene was quite frequent in the healthy Indian population and was significantly (P=6.35×10^–6) lower in RA patients. We replicated this association (P=1.78×10^–5) in an independent cohort of control individuals. Promoter polymorphism at –550 nt showed a significant overrepresentation (P=0.003) of the minor allele G in severe RA patients compared with the less severe group. Haplotype LYA frequency was significantly (P=0.03) high in the less severe group, while the frequency of the HYA haplotype was significantly (P=0.04) increased in the severe RA patients. No statistically significant difference in serum MBL2 was observed as a whole, but the individuals homozygous for the LYA haplotype had significantly lower (P=0.017) serum MBL2 levels compared with individuals homozygous for the HYA haplotype. Therefore, the B variant of the MBL2 gene may be associated with protection from RA in our study population, and the promoter polymorphism (–550 nt) seems to have some role in disease progression.     

High-producing MBL2 genotypes increase the risk of acute and chronic carditis in patients with history of rheumatic fever

Rheumatic fever (RF) and its most severe sequela, chronic rheumatic heart disease (CRHD), are mediated by an abnormal immunological host response following a Streptococcus pyogenes oropharyngeal infection. Mannan-binding lectin (MBL), a collectin that activates complement, binds to N-acetylglucosamine, a molecule present on the streptococcus cell wall and on human heart valves. As high levels of MBL and MBL2 associated genotypes have previously been seen to be associated with CRHD, we investigated the association between MBL2 polymorphisms and the presence of acute carditis and arthritis in patients with a history of RF. Polymorphisms in exon 1 and in the X/Y promoter region of the MBL2 gene were determined by PCR-SSP in 149 patients with a history of RF and 147 controls. Genotypes associated with the high production of MBL (YA/YA and YA/XA) were more frequent in the patients with acute (26/35, 74%) and chronic carditis (79/107, 74%) when compared to the controls (79/147, 54%; OR 2.48, 95% CI 1.09-5.67, p=0.035 and OR 2.42, 95% CI 1.41-4.16, p=0.001, respectively). Logistic regression analysis showed that MBL levels >2800ng/ml increased the risk of CRHD (OR 2.91, 95% CI 1.41-6.03, p=0.003). Among the RF patients without cardiac sequela, YA/YA and YA/XA genotypes were significantly associated with acute carditis when compared to the patients without this clinical manifestation (26/28, 93% vs. 9/14, 64%, OR 7.22, 95% CI 1.18-43.98, p=0.031); on the other hand, arthritis was more frequently observed in those patients presenting MBL2 genotypes related to the low production of MBL (10/14, 71% vs. 10/28, 36%; p=0.048, OR 0.22, 95% CI 0.05-0.89). We concluded that MBL2 genotypes associated with the high production of MBL seem to be involved in the pathogenesis of rheumatic carditis and its progression to CRHD.     

Association of a new mannose-binding lectin variant with severe malaria in Gabonese children

Mannose-binding lectin (MBL2) variants that decrease the plasma level of the protein or encode dysfunctional proteins are frequently associated with the severity of a number of infections and autoimmune disorders. The high frequencies of these variants in most populations of the world are probably maintained by some selective advantage against widespread diseases. We found 14 new MBL2 allelic haplotypes, two of them with non-synonymous variants, by screening 136 children with uncomplicated malaria, 131 children with severe malaria and 39 older healthy schoolchildren. We also found a significant association of a novel variant with susceptibility to severe malaria (P=0.010). Increased MBL plasma levels and corresponding MBL2 genotypes were associated with lower concentration of several cytokines and chemokines in plasma of malaria patients. We suggest that malaria could have been one of the evolutionary driving forces shaping the MBL2 polymorphism in the African population.     

A new strategy for mannose-binding lectin gene haplotyping

The mannose-binding lectin 2 (MBL2) gene is polymorphic and codes for a protein with an important role in the innate immune response, whose variants have been associated with a great number of diseases. Point variations have been described in the 5' regulatory region at positions -550 (MBL2*H or *L) and -221 (*X or *Y), in the 5' untranslated sequence at position +4 (*P or *Q), and in the coding sequence of exon 1 at codons 52, 54, and 57 (MBL2*A or D, A or B, and A or C, respectively). These can be in cis or in trans configuration. The different haplotypes influence the immunological phenotype of the individual, which makes MBL2 haplotyping very important. Previously described MBL2-typing methods do not present adequate haplotype resolution or are too complex and costly. We have developed a new MBL2-typing strategy that is economical and renders rapid and reliable results without ambiguities. We typed 202 individuals of European, 32 of African, and 16 of Oriental descent. Only five to six reactions from 10 possible PCR-SSPs (sequence-specific polymerase chain reactions) were sufficient to genotype one individual unambiguously. The reactions were specific for amplification of the variants located upstream of the coding sequence. The results were associated to the results of hybridizations of the amplified products with eight sequence-specific oligonucleotide probes (SSOP). The strategy led to identification of eight alleles: MBL2*HYPA, HYPD, LYPA, LYPB, LYPD, LYQA, LYQC, and LXPA. Their frequencies in each of the groups were similar to those of other populations studied to date, with MBL2*LYPD (g.[-550G>C; -221C>G; 4T>C; 223C>T; 230A>G; 239A>G]) being novel. All samples were found to be in Hardy-Weinberg equilibrium.     

Lack of association between hepatitis B virus infection and polymorphism of mannose-binding lectin gene in Korean population

Mannose-binding lectin (MBL) plays an important role in immune defense. This study was undertaken to investigate the association between hepatitis B virus infection and polymorphisms of MBL gene. We assessed the single nucleotide polymorphism at codon 54 in exon 1 of MBL in patients with hepatitis B virus infection and HBsAg negative controls in Korean population. A total of 498 enrolled subjects was classified into four groups. Group 1; Clearance, Group 2; Inactive healthy carrier, Group 3; Chronic hepatitis, Group 4; Liver cirrhosis. MBL gene polymorphisms at codon 54 led to three genotypes (G/G, G/A, A/A). When we divided subjects into clearance group (group 1) and persistence group (group 2-4), G/G genotype and A-allele carrier were observed in 55.6% and 44.4% in clearance group, 64.8% and 35.2% in persistence group (p=0.081), respectively. When hepatitis B virus persistent cases were divided into inactive healthy carrier (group 2) and disease progression group (group 3 and 4), MBL gene polymorphisms at codon 54 were not related to disease progression (p=0.166). MBL gene polymorphism at codon 54 was not associated with the clearance of hepatitis B virus infection nor progression of disease in chronic hepatitis B virus infection.     

Mannan-binding lectin in children with Escherichia coli O157:H7 haemmorrhagic colitis and haemolytic uraemic syndrome

Mannan-binding lectin (MBL) triggers complement activation upon binding to microbial surfaces. MBL deficiency has been associated with increased susceptibility to severe bacterial infections. We hypothesized that MBL deficiency may predispose children to Shiga toxin-producing Escherichia coli (STEC) O157:H7 infections and the associated haemolytic uraemic syndrome (HUS). We compared circulating levels of MBL among children with uncomplicated O157:H7 haemorrhagic colitis (HC), patients with O157:H7 HUS, normal and diseases control groups. Circulating MBL concentrations on admission were as follows: 3.22 +/- 2.43 micro g/ml among normal controls (n = 23); 2.90 +/- 2.44 micro g/ml in patients with rotavirus enteritis (n = 10); 2.78 +/- 1.65 micro g/ml in children with HC due to non-STEC bacterial pathogen (n = 15); 2.67 +/- 2.44 micro g/ml in patients with uncomplicated O157:H7 HC (n = 27); 2.80 +/- 2.97 micro g/ml in children with O157:H7 HUS (n = 15); 6.70 +/- 4.49 micro g/ml in patients with chronic renal failure unrelated to O157:H7 infection (n = 6). Higher MBL levels were found in patients with chronic renal failure compared to O157:H7 HC (P < 0.047). However, MBL concentrations <0.5 micro g/ml, which have been associated with MBL deficiency in relation to increased susceptibility to infections, were noted at comparable rates between the different groups (P = NS). Our data does not support that MBL deficiency may predispose to O157:H7 infections nor than the development of diarrhoea associated HUS.     

Influence of mannose-binding lectin on HIV infection and tuberculosis in a Western-European population

Mannose-binding lectin (MBL) is a serum lectin that mediates phagocytosis and activates complement. Its deficiency has been associated with increased susceptibility to infectious diseases, mainly in childhood. However, non-producer mbl-2 alleles are common in most populations, suggesting a selective advantage of these alleles. We have analysed the association of mbl-2 structural and promoter polymorphisms with HIV infection and tuberculosis (TBC) in a white Spanish population, including 615 HIV patients with and without TBC, 127 no-HIV TBC patients, 142 TBC household contacts and 344 controls. The frequency of low or non-producer mbl-2 genotypes was lower in HIV patients than in controls. HIV-TBC patients presented lower frequencies of low or non-producer alleles and genotypes than HIV no-TBC patients and controls. Additionally, we found a significantly positive correlation between the incidence of TBC and the frequency of non-producer mbl-2 alleles in Western Europe. Therefore, MBL deficiency may be associated with a lower risk of HIV infection, and also of active TBC, at least in HIV patients. The protective role of low-producer mbl-2 genotypes against TBC together with the positive correlation observed between non-producer mbl-2 alleles and TBC incidence, suggest a balancing selection: in spite of an increased susceptibility to respiratory infections associated with MBL deficiency, mbl-2 deficient alleles would have been selected along different populations as a consequence of its selective advantage against intracellular pathogens, such as M. tuberculosis.     

Mannose-binding lectin gene (MBL2) polymorphisms related to the mannose-binding lectin low levels are associated to dengue disease severity

Dengue is the main arbovirosis in the tropical and subtropical areas of the world. The majority of infected individuals present an asymptomatic outcome while others progress to dengue fever (DF) or dengue haemorrhagic fever (DHF). Dengue infection evolution to severe outcomes is in part, related to innate immunity response. The MBL2 gene encodes for a pathogen recognition pattern molecule, the mannose-binding lectin (MBL). Variant alleles at promoter and structural regions of the MBL2 are related to serum MBL levels and function. Due to the important inflammatory modulation role of MBL, MBL2 polymorphisms could influence dengue progression. Therefore, this study investigated associations of MBL2 polymorphisms and serum MBL levels in patients with dengue. Genotyping of promoter and structural regions of MBL2 was performed by real-time PCR using Taqman® probes in 161 patients presenting DF or DHF outcome. For the serum MBL determination a commercial ELISA kit was used. The variant OO genotype and O allele were associated with DHF (p = 0.008 and p = 0.009 respectively). Haplotypes correlated to MBL low levels were associated with DHF (p = 0.04). Our results support the hypothesis that patients carrying genotypes or haplotypes of low production of MBL would be more susceptible to DHF.     

Restricted polymorphism of the mannose-binding lectin gene of indigenous Australians

Mannose-binding lectin (MBL) is an important complement-activating protein of the human innate immune system. Deficiency of MBL is associated with an increased risk of various infections and arises from three structural gene mutations in exon 1 (variants B, C and D) and/or the presence of a low efficiency promoter. The C allele is found in sub-Saharan Africa whereas the B allele is found elsewhere, suggesting that these mutations occurred after the suggested hominid migration out of Africa [100-150 000 years before present (BP)]. Paradoxically, these alleles may have a selective advantage in protection against intracellular pathogens and occur at particularly high frequencies in sub-Saharan Africa (C variant) and South America (B variant). Since hominids reached Australia at least 50 000 years ago, a study of MBL polymorphisms in the indigenous population was of interest. Using heteroduplex technology we found a paucity of MBL structural gene mutations in two population groups from geographically distinct regions. Of 293 individuals tested, 289 were wild-type and four were heterozygous for either the B or D allele. In each individual with an MBL mutation the HLA haplotype profile suggested some Caucasian admixture. We also found a restricted range of MBL promoter haplotypes and the serum MBL levels were higher than those of any other ethnic group studied to date (median 3.07 microg/ml). Our data suggest that the B mutation probably arose between 50 000 and 20 000 BP. Its absence from the founder gene pool of indigenous Australians may also partly explain their vulnerability to intracellular infections such as tuberculosis.     

Association between mannose-binding lectin deficiency and septic shock following acute pyelonephritis due to Escherichia coli

Structural and promoter MBL2 gene polymorphisms responsible for low MBL levels are associated with increased risk of infection. The objective of this study was to assess the possible association between polymorphisms of the MBL2 gene and the incidence of septic shock and bacteremia in patients with acute pyelonephritis due to Escherichia coli. The study included 62 female patients with acute pyelonephritis due to E. coli who required hospital admission, as well as 133 healthy control subjects. Six single-nucleotide polymorphisms (-550 G/C, -221 C/G, +4 C/T, codon 52 CGT/TGT, codon 54 GGC/GAC, and codon 57 GGA/GAA) in the MBL2 gene were genotyped by using a sequence-based typing technique. No significant differences were observed in the frequencies for low-expression MBL2 genotypes (O/O and LXA/O) between patients with acute pyelonephritis and healthy controls. Patients with acute pyelonephritis and septic shock had a higher incidence of low-expression MBL2 genotypes than patients with acute pyelonephritis without septic shock (odds ratio = 9.019, 95% confidence interval = 1.23 to 65.93; P = 0.03). No association was found between bacteremic acute pyelonephritis and low-expression MBL2 genotypes. We found that low-expression MBL2 genotypes predispose to septic shock but not to bacteremia in patients with E. coli-induced acute pyelonephritis. Determination of MBL2 polymorphisms could be useful for assessing the risk of septic shock in women undergoing acute pyelonephritis.     

High prevalence of mannose-binding lectin (MBL) deficiency in premature neonates

Mannose-binding lectin (MBL) is a component of innate immunity and thus particularly important in neonates in whom adaptive immunity is not yet completely developed. Promoter polymorphisms and structural exon-1 mutations in the MBL2 gene cause reduced or deficient MBL plasma concentrations. The aim of our study was to determine the prevalence of MBL deficiency in neonates admitted to the neonatal intensive care unit (NICU). Eighty-five NICU patients (69 premature) were included in the study. We measured MBL concentrations in umbilical cord and neonatal blood within 24 h after birth by ELISA technique. MBL2 genotypes (n = 67) were determined by Taqman analysis. MBL concentrations were measured longitudinally during three weeks in 26 premature neonates. The association between pre- and intra-partum clinical data and MBL concentrations was investigated. At birth, 29 (42%) premature and six (38%) term neonates had MBL plasma concentrations < or = 0.7 microg/ml which was regarded as deficient. Twenty-one (38%) premature and four (36%) term neonates had variant MBL2 haplotypes, corresponding to exon-1 mutations and the LXPA haplotype. MBL concentrations increased over time in neonates with wild-type MBL2 haplotypes, but not in neonates with variant haplotypes. Low MBL plasma concentrations were related to lower gestational age and variant MBL2 haplotypes. Umbilical cord and neonatal MBL plasma concentrations appeared to be similar. In conclusion, almost half of our NICU patients, especially the premature ones, were MBL-deficient at birth. These infants may be at increased risk of neonatal infections. MBL concentration can reliably be measured in umbilical cord blood and it is positively correlated with gestational and postnatal age.     

Association between combined properdin and mannose-binding lectin deficiency and infection with Neisseria meningitidis

BACKGROUND: Individuals genetically deficient of properdin are more susceptible to meningococcal disease. Likewise low concentration or decreased biological activity of mannose-binding lectin (MBL) is associated with higher incidence of bacterial infections during childhood. In this study we report our findings in a Danish family with a remarkably high incidence of meningococcal meningitis-in total four cases, one of them fatal. METHODS: Properdin and MBL were quantified by ELISA and the properdin gene was screened for sequence variations using denaturing high-performance liquid chromatography (DHPLC) and subsequent sequencing of abnormal patterns. The MBL gene was genotyped for the three known variant alleles (B, C and D) as well as three promoter polymorphisms (-221Y/X, -550H/L and +4P/Q). RESULTS: Two out of six males with undetectable properdin activity had meningitis. They had also low MBL serum levels or carried an MBL variant allele, whereas high MBL concentrations were measured in three out of four properdin deficient males--without meningitis. A splice site mutation in exon 10 (c.1487-2A>G) was found in the properdin gene and co segregated with biochemically measured properdin deficiency. CONCLUSION: Our results indicate that a combined deficiency of both properdin and MBL increases the risk of infection with Neisseria meningitidis and stress the importance of epistatic genetic interactions in disease susceptibility.     

Increased frequency of the mannose-binding lectin LX haplotype in Chinese systemic lupus erythematosus patients.

Mannose-binding lectin (MBL) is an important complement-activating protein of the human immune system. As a result of one of three structural gene mutations in exon 1 (variants B, C and D) and/or the presence of a low-efficiency promoter polymorphism, MBL deficiency may be associated with increased susceptibility to infectious diseases and to autoimmune disorders, including systemic lupus erythematosus (SLE). Using a combined approach of heteroduplex generator and polymerase chain reaction, a systematic search for mutations in exon 1 and the promoter region of the MBL gene was performed in a Chinese study population comprising 41 SLE patients and 111 healthy controls. Two alleles, a wild-type allele A and a variant allele B (a previously reported mutation of GGC to GAC at codon 54), were identified in MBL exon 1. The frequency of the B allele (0.15) was higher in the SLE patients than in the healthy controls (0.09), but the difference did not attain statistical significance (P > 0.05). However, for two polymorphisms at positions -550 and -221 in the promoter region, the frequency of the low-MBL-producing haplotype (LX) in the patients (0.2073) was significantly higher than that in the controls (0.0855) (P = 0.003, relative risk = 2.79). Our results suggest that the LX haplotype represents a strong risk factor among Chinese SLE patients. Although of lesser importance, the MBL B allele also may be a risk component in the developing process of SLE in Chinese patients.