Association of mannose-binding lectin gene variation with disease severity and infections in a population-based cohort of systemic lupus erythematosus patients

Infections in systemic lupus erythematosus

Infections are an important cause of morbidity and mortality in systemic lupus erythematosus (SLE). Survival rates for SLE patients in developing countries are comparatively lower than those reported in industrialized countries, with early death from infection and active disease. In addition to the role of immunosuppressive agents in enhancing susceptibility to infection, infectious agents are also known to trigger lupus disease expression and activity. The endemicity of certain infections like tuberculosis further poses a special health issue in developing countries.

Association of mannose-binding lectin gene polymorphisms with Kawasaki disease in the Japanese

OBJECTIVE

Kawasaki disease (KD) is a systemic vasculitis in childhood; its etiology is unknown. The possibility that KD is an infectious disease has been discussed and investigated for decades, in light of the implication that infections are involved in the pathogenesis of KD. Young children rely on their innate immune system for protection against virus and micro-organisms. Human mannose binding lectin (MBL) is a C-type serum lectin synthesized by the liver as an acute phase protein and it plays an important role in the innate immune system. Here, we investigate the relationship between the MBL gene polymorphisms and the occurrence of KD in the Japanese population.

METHOD

The frequencies of the genotypes, defined as mutations in codons 52, 54 and 57, and the functional promoter variants of the MBL were determined in 45 patients with KD.

RESULTS

The MBL codon-54 polymorphism frequency of heterozygote (GGC/GAC) and promoter variants were significantly higher in the KD group than that in the control group (P < 0.05). Neither group showed codon 52 nor 57 polymorphisms.

CONCLUSION

It is possible that mutations of the MBL gene might be related to the trigger of the pathogenesis of Kawasaki disease.

Recombinant form of human wild type mannan-binding lectin (MBL/A) but not its structural variant (MBL/C) promotes phagocytosis of zymosan by activating complement

Mannan-binding lectin (MBL) mediates innate immune responses, such as activation of the complement lectin pathway and phagocytosis, to help fight infections. In the present study, employing recombinant forms of human MBL (rMBL), the role of wild type MBL (rMBL/A) and its structural variant rMBL/C in mediating THP-1 phagocytosis of fluorescent-labeled zymosan was examined and compared to MBL purified from human plasma (pMBL/A). Flow cytometric analyses revealed that opsonization of zymosan with rMBL/A and pMBL/A (0.5-30microg/ml) resulted in a 1.9- and 2.7-fold enhancement in its uptake by THP-1 cells in the presence of serum that was depleted of both MBL and the classical pathway component, C1q (MBL/C1q Dpl serum). In contrast, no enhancement in phagocytosis was observed when zymosan was opsonized with rMBL/C. Addition of MBL monoclonal antibody, EDTA, or mannan to the opsonization reaction mixture inhibited THP-1 phagocytosis of pMBL/A opsonized zymosan. Heat inactivation of MBL/C1q Dpl serum abolished the 2-fold increase in phagocytosis and in the absence of serum the direct opsonic activity of MBL did not contribute significantly to the uptake of zymosan into THP-1 cells. Activation products of complement components C3 and C4 were deposited on zymosan opsonized with pMBL/A and rMBL/A but not rMBL/C indicating that MBL-mediated phagocytosis of zymosan requires activation of the complement lectin pathway. The findings imply that impaired MBL-mediated phagocytosis may put individuals homozygous for the mutant allele MBL/C but not wild type MBL/A at increased risk to infections such as yeast.

APOE epsilon4 and MBL-2 O/O genotypes are associated with neurocognitive impairment in HIV-infected plasma donors

BACKGROUND

Host genetic factors are important determinants for risk of HIV-1 infection and disease progression. This study examined associations of host genetic variants and neurocognitive impairment in Chinese individuals infected through contaminated blood products.

METHODS

Two hundred and one HIV-infected patients from Anhui, China, had neuropsychological tests at baseline and 12 months. DNA was genotyped for APOE epsilon2, epsilon3 and epsilon4 alleles; MBL2-A/O; CCR5-wt/Delta32; CCR5-59029-G/A; CCR2-180-G/A; SDF-1-G/A; IL4-589-C/T; MCP-1-2518-A/G; CX3CR1-745-G/A; -849-C/T polymorphisms and CCL3L1 copy number variants using real-time PCR. Univariate and multivariate analyses were performed.

RESULTS

The cohort included 61% men, with mean education 5.5 years, AIDS diagnosis 113 (55%), on antiretrovirals 114 (56%), mean baseline CD4(+) cell count 349 cells/microl and mean log10 RNA 4.09. At baseline, 37% had global neuropsychological impairment increasing to 44% after 12 months. Of 43 patients with the APOE epsilon4 allele, 58% were cognitively impaired compared with 31% without the epsilon4 allele (P = 0.001, odds ratio 3.09, 95% confidence interval 1.54-6.18). The mean global deficit score (GDS) for epsilon4-positive participants on antiretrovirals for 12 months was 0.88 (0.55) compared with 0.63 (0.54) for epsilon4-negative participants (P = 0.053, 95% confidence interval -0.004 to 0.51). For MBL2, 52% of patients with the O/O genotype declined in cognitive function over 12 months compared with 23% with A/A (odds ratio 3.62, 95% confidence interval 1.46-9.03, P = 0.004). No associations were observed for the other genetic variants.

CONCLUSION

The APOE epsilon4 allele was associated with increased risk for cognitive deficits, whereas the MBL2 O/O genotype was associated with increased risk for progressive cognitive decline in Chinese individuals infected with HIV through contaminated blood products.

Systemic lupus erythematosus and ethnicity: nature versus nurture or nature and nurture?

Ethnic variation in the frequency and outcome of systemic lupus erythematosus (SLE) has been recognized for decades. The reasons underlying these discrepancies are not completely understood but it is most likely that both genetic and nongenetic factors are responsible for them. Sorting out the extent to which these factors, particularly those of a nongenetic nature, exert their influence in SLE is not easy given inherent methodological difficulties in studying them. To establish this review properly, we would like to make it clear from the outset that ethnicity is a broad construct that implies not only biological but also nonbiological features including cultural and sociodemographic, among others. We will then describe the epidemiological differences of SLE among Caucasian and non-Caucasian populations followed by a succinct review of the genetic predisposition to SLE with special emphasis in ethnic heterogeneity. Differences in disease activity, lupus nephritis, damage and mortality as a function of ethnic group will then be described. Finally, we will present a comprehensive model of the influence of ethnicity on SLE.

Dendritic cell function in lupus: Independent contributors or victims of aberrant immune regulation

Dendritic cells (DCs) represent an important component of the immune system connecting the innate and adaptive immune responses. They are able to trigger strong immunity as well as tolerance against certain antigens, and therefore it is obvious that they have a central role in the expression of immunological diseases. However, because DCs are sparse, heterogeneous and plastic, their exact role in complex autoimmune diseases, such as systemic lupus erythematosus (SLE) remains not well defined. In this review, we make an attempt to summarize critically recent knowledge on the role of conventional DCs in the expression of autoimmunity and pathology in SLE.

Childhood exposure to secondhand smoke and functional mannose binding lectin polymorphisms are associated with increased lung cancer risk

BACKGROUND

Exposure to secondhand smoke during adulthood has detrimental health effects, including increased lung cancer risk. Compared with adults, children may be more susceptible to secondhand smoke. This susceptibility may be exacerbated by alterations in inherited genetic variants of innate immunity genes. We hypothesized a positive association between childhood secondhand smoke exposure and lung cancer risk that would be modified by genetic polymorphisms in the mannose binding lectin-2 (MBL2) gene resulting in well-known functional changes in innate immunity.

METHODS

Childhood secondhand smoke exposure and lung cancer risk was assessed among men and women in the ongoing National Cancer Institute-Maryland Lung Cancer (NCI-MD) study, which included 624 cases and 348 controls. Secondhand smoke history was collected via in-person interviews. DNA was used for genotyping the MBL2 gene. To replicate, we used an independent case-control study from Mayo Clinic consisting of 461 never smokers, made up of 172 cases and 289 controls. All statistical tests were two-sided.

RESULTS

In the NCI-MD study, secondhand smoke exposure during childhood was associated with increased lung cancer risk among never smokers [odds ratio (OR), 2.25; 95% confidence interval (95% CI), 1.04-4.90]. This was confirmed in the Mayo study (OR, 1.47; 95% CI, 1.00-2.15). A functional MBL2 haplotype associated with high circulating levels of MBL and increased MBL2 activity was associated with increased lung cancer risk among those exposed to childhood secondhand smoke in both the NCI-MD and Mayo studies (OR, 2.52; 95% CI, 1.13-5.60, and OR, 2.78; 95% CI, 1.18-3.85, respectively).

CONCLUSIONS

Secondhand smoke exposure during childhood is associated with increased lung cancer risk among never smokers, particularly among those possessing a haplotype corresponding to a known overactive complement pathway of the innate immune system.

Infection in systemic lupus erythematosus: friend or foe?

Infectious agents have long been implicated in the pathogenesis of systemic lupus erythematosus. Common viruses, such as the Epstein-Barr virus, transfusion transmitted virus, parvovirus and cytomegalovirus, have an increased prevalence in patients with systemic lupus erythematosus. They may contribute to disease pathogenesis through triggering autoimmunity via structural or functional molecular mimicry, encoding proteins that induce cross-reactive immune responses to self antigens or modulate antigen processing, activation, or apoptosis of B and T cells, macrophages or dendritic cells. Alternatively, some infectious agents, such as malaria, Toxoplasma gondii and Helicobacter pylori, may have a protective effect. Vaccinations may play dual roles by protecting against friend and foe alike.

Infection—genetics relationship in systemic lupus erythematosus

Genetic, environmental, and hormonal factors contribute to disease susceptibility in systemic lupus erythematosus. Among environmental factors, infectious agents play a major role. When considering the complex relationship between genetic predisposition and infections in the pathogenesis of systemic lupus erythematosus, we have to consider that infectious agents can interact with the immune system in several ways. For example, molecular mimicry, altered apoptosis of the host cells, exposure of as yet masked antigens to the immune system by a given microorganism, and direct viral invasion of immunocompetent cells are all mechanisms that may give rise to dysfunction of the immune system; in addition, some genetically determined deficit of the immune system, such as complement deficiency or deficit of mannose binding lectine, may cause insufficient clearance of infectious agents, whose persistence in the host may determine autoimmunity. Finally, evidence has been emerging suggesting that the production of autoantibodies, by infected B-lymphocytes, may be drawn by altered expression of particular microRNA in these cells. In this paper, we review some of the distinct scenarios that can account for the role of infectious agents, acting on a genetically prone host, in determining systemic lupus erythematosus.

Clinical significance of complement deficiencies

The complement system is composed of more than 30 serum and membrane-bound proteins, all of which are needed for normal function of complement in innate and adaptive immunity. Historically, deficiencies within the complement system have been suspected when young children have had recurrent and difficult-to-control infections. As our understanding of the complement system has increased, many other diseases have been attributed to deficiencies within the complement system. Generally, complement deficiencies within the classical pathway lead to increased susceptibility to encapsulated bacterial infections as well as a syndrome resembling systemic lupus erythematosus. Complement deficiencies within the mannose-binding lectin pathway generally lead to increased bacterial infections, and deficiencies within the alternative pathway usually lead to an increased frequency of Neisseria infections. However, factor H deficiency can lead to membranoproliferative glomerulonephritis and hemolytic uremic syndrome. Finally, deficiencies within the terminal complement pathway lead to an increased incidence of Neisseria infections. Two other notable complement-associated deficiencies are complement receptor 3 and 4 deficiency, which result from a deficiency of CD18, a disease known as leukocyte adhesion deficiency type 1, and CD59 deficiency, which causes paroxysmal nocturnal hemoglobinuria. Most inherited deficiencies of the complement system are autosomal recessive, but properidin deficiency is X-linked recessive, deficiency of C1 inhibitor is autosomal dominant, and mannose-binding lectin and factor I deficiencies are autosomal co-dominant. The diversity of clinical manifestations of complement deficiencies reflects the complexity of the complement system.

Circulating Surfactant Protein D Is Decreased in Systemic Lupus Erythematosus

Objective.

Deficiencies of innate immune molecules like mannan binding lectin (MBL) have been implicated in the pathogenesis of systemic lupus erythematosus (SLE). Surfactant protein D (SP-D) and MBL belong to the same family of innate immune molecules — the collectins, which share important structural and functional properties. We aimed to compare concentrations of serum SP-D in patients with SLE and in healthy controls, and to investigate if SP-D is associated with selected disease indicators. We investigated the possible association of the Met11Thr polymorphism with disease, since this polymorphism is an important determinant for serum level, oligomerization pattern, and function of SP-D.

Methods.

Serum SP-D was measured using a 5-layer ELISA in 70 SLE patients and 1476 healthy subjects. DNA was genotyped for the Met11Thr variant.

Results.

Median SP-D level in serum was 911 ng/ml (95% CI 776–1118) in patients and 1068 ng/ml (95% CI 901–1246) in controls (p = 0.0004). Circulating SP-D did not differ significantly in patients with high, intermediate, or low SLE disease activity. Similarly, SP-D did not correlate with C-reactive protein, erythrocyte sedimentation rate, and anti-dsDNA seropositivity. Genetic analysis did not support an association of the Met11Thr genotype with SLE.

Conclusion.

These findings suggest that low SP-D, unrelated to conventional disease indicators, represents an aspect of SLE etiopathogenesis.

Malignancy in systemic lupus erythematosus: what have we learned?

What have we learnt about cancer risk in systemic lupus erythematosus (SLE) over the past decade? One important lesson is that data do confirm a slightly increased risk in SLE for all cancers combined, compared to that in the general population. However, it is clear that this is largely driven by an increased risk for haematological malignancies, particularly non-Hodgkin's lymphoma (NHL), although Hodgkin's lymphoma may be increased as well. In addition, there is evidence for a moderately increased risk of lung cancer, and possibly for rarer cancer types such as hepatobiliary and vulvar/vaginal malignancies. Unfortunately, the most clinically relevant question--the mechanism underlying the association between cancer and SLE--remains largely unanswered. Key issues remaining relate to the links between cancer risk, SLE disease activity, and medication exposures. Much of the recent data suggest that disease-related factors may be at least as important as medication exposures for certain cancers, such as NHL. The independent effects of drug exposures versus disease activity in mediating cancer risk in SLE remain unknown. Work is in progress to further elucidate these important issues. Meanwhile, there is good evidence that cervical dysplasia is increased in women with SLE. This may be mediated by decreased clearance of the human papilloma virus, which some suggest is an innate characteristic of SLE patients. However, an increased risk of cervical dysplasia is also associated with immunosuppressive medication exposures, particularly cyclophosphamide. For these reasons, it is important that women with SLE follow established guidelines for cervical cancer screening.

Accelerated atherosclerosis, arterial thromboembolism, and preventive strategies in systemic lupus erythematosus

With improved disease survival, arterial thromboembolism has become an important cause of morbidity in patients with systemic lupus erythematosus (SLE). A number of conventional and non-conventional risk factors are associated with accelerated atherosclerosis. Regular surveillance and control of traditional risk factors is mandatory, and so is the appropriate use of the statins, anti-malarial agents, anti-platelet agents, and anti-coagulation for primary and secondary prevention of arterial thromboembolism in SLE patients. Judicious use of corticosteroids, calcineurin inhibitors, hormonal replacement therapy, and the cyclooxygenase 2 inhibitors is equally important.

Structural polymorphism of the mannose-binding lectin 2 (MBL2 ) gene in HCV-infected patients with a serological marker for thyroid autoimmunity

We studied the association of the mannose-binding lectin-2 (MBL2) polymorphism with anti-thyroid antibodies (ATA) in hepatitis C virus (HCV)-infected Brazilian patients (n = 162) and 124 healthy volunteers screened for ATA. Our results showed that patients with ATA had higher frequency of genotype 00 than controls. MBL may play a role as disease modifier in HCV infection.

Murine Lupus Autoantibodies Identify Distinct Subsets of Apoptotic Bodies

The specific modification of autoantigens and their redistribution into blebs at the surface of apoptotic cells contribute to the induction of autoimmune responses. Blebs containing fragments of the apoptotic nucleus separate from the remainder of the cell to form membrane-bound sub-cellular particles (SCPs), otherwise known as apoptotic bodies. To determine whether apoptotic bodies containing nuclear antigens represent a defined subset of SCPs, we examined the heterogeneity of particles generated by Jurkat cells following synchronization of the cell cycle by serum withdrawal and inhibition of topoisomerase I by camptothecin. Particles were purified by filtration, incubated in the presence of antinucleosome or anti-cardiolipin autoantibodies, annexin V, and Sytox Orange and analyzed by flow cytometry and confocal microscopy. We demonstrate that nuclear autoantigens are associated with one clearly defined subset of SCPs that can be distinguished from other products of late apoptosis. Our experiments represent an important step towards characterizing the heterogeneity of SCPs that are generated in late apoptosis and identifying their contributions to tolerance and autoimmunity.

Bench-to-bedside review: Association of genetic variation with sepsis

Susceptibility and response to infectious disease is, in part, heritable. Initial attempts to identify the causal genetic polymorphisms have not been entirely successful because of the complexity of the genetic, epigenetic, and environmental factors that influence susceptibility and response to infectious disease and because of flaws in study design. Potential associations between clinical outcome from sepsis and many inflammatory cytokine gene polymorphisms, innate immunity pathway gene polymorphisms, and coagulation cascade polymorphisms have been observed. Confirmation in large, well conducted, multicenter studies is required to confirm current findings and to make them clinically applicable. Unbiased investigation of all genes in the human genome is an emerging approach. New, economical, high-throughput technologies may make this possible. It is now feasible to genotype thousands of tag single nucleotide polymorphisms across the genome in thousands of patients, thus addressing the issues of small sample size and bias in selecting candidate polymorphisms and genes for genetic association studies. By performing genome-wide association studies, genome-wide scans of nonsynonymous single nucleotide polymorphisms, and testing for differential allelic expression and copy number polymorphisms, we may yet be able to tease out the complex influence of genetic variation on susceptibility and response to infectious disease.

Immunity and acquired alterations in cognition and emotion: lessons from SLE

Classic immunologic teaching describes the brain as an immunologically privileged site. Studies of neuroimmunology have focused for many years almost exclusively on multiple sclerosis, a disease in which inflammatory cells actually infiltrate brain tissue, and the rodent model of this disease, experimental allergic encephalitis. Over the past decade, however, increasingly, brain-reactive antibodies have been demonstrated in the serum of patients with numerous neurological diseases. The contribution these antibodies make to neuronal dysfunction has, in general, not been determined. Here, we describe recent studies showing that serum antibodies to the N-methyl-D-aspartate receptor occur frequently in patients with systemic lupus erythematosus and can cause alterations in cognition and behavior following a breach in the blood-brain barrier.

New insights on the structural/functional properties of recombinant human mannan-binding lectin and its variants

Inefficient activation of complement lectin pathway in individuals with variant mannan-binding lectin (MBL) genotypes has been attributed to poor formation of higher order oligomers by MBL. But recent studies have shown the presence of large oligomers of MBL (approximately 450 kDa) in serum of individuals with variant MBL alleles. The recombinant forms of MBL (rMBL) variants except MBL/B that assemble into higher order oligomers have not yet been reported. In the present study, structural/functional properties of recombinant forms of wild type MBL (rMBL/A) and its three structural variants, rMBL/B, C, and D generated in insect cells were examined. Western blot analysis indicated covalently linked monomers to hexamers while gel filtration chromatography exhibited non-covalently linked higher order oligomers in addition to prevalent low oligomeric forms. Mannan binding determined by ELISA showed rMBL/A but not the structural variants bind to mannan. Apparent avidity of monoclonal antibody used was found to be about 18- to 52-fold weaker for rMBL structural variants than rMBL/A. Complement activation varied with maximum impairment apparent in rMBL/C followed by rMBL/B, but rMBL/D was functional to the same extent as rMBL/A. Comparison of rMBL/A to MBL purified from plasma (pMBL/A) indicated 8- and 24-fold weaker binding to mannan by BIAcore analysis and ELISA and about 5-fold lesser efficiency in activating complement. The findings provide new insights on the structural/functional properties of rMBL variants and imply that lectin pathway activation may be impaired in individuals, homozygous for the mutant alleles, MBL/C and to a lesser extent MBL/B but not MBL/D.

MBL2 single nucleotide polymorphism diversity among four ethnic groups as revealed by a bead-based liquid array profiling

In the present work we established a rapid, cost-effective and high-throughput method for genotyping using a multiplexed microsphere-based suspension array platform - Luminex xMAP which enabled us to analyze 3 SNPs in the MBL2 gene promoter and 5' UTR, and 3 coding SNPs exon 1 haplotypes, associated with different levels of MBL2 expression. Using this system MBL2 diversity in four different ethnic groups, namely, Asian (Japanese), Caucasian, Hispanic and African-American-assessed. Results showed significant variability in terms of allele, genotype, and haplotype distribution. Characteristic MBL haplotype patterns were defined for each ethnic group. A prevalence of haplotypes coding functional proteins capable of complement activation and pathogen opsonization was observed. Regardless of the significant diversity of individual haplotypes, a high, almost similar (25-28%) proportion of haplotypes associated with MBL deficiency was found in the four ethic groups. The proportion of individuals homozygous for the haplotypes resulting in complete MBL2 deficiency was also significant (2-10%). Considering the role of MBL2 in innate immunity and as a clinically relevant marker, the genotyping approach developed and the knowledge of the genetic variation in different ethnic groups will be relevant to future medical genetic studies.

Detrimental effects of mannose-binding lectin (MBL2) promoter genotype XA/XA on HIV-1 vertical transmission and AIDS progression

BACKGROUND

The literature on the involvement of mannose-binding lectin (MBL) in human immunodeficiency virus (HIV) transmission and acquired immunodeficiency syndrome (AIDS) is conflicting. Polymorphisms in the MBL2 gene reduce the level of protein and alter its structure. Thus, we investigated whether MBL2 alleles and plasma concentrations of MBL are associated with perinatal HIV transmission and disease progression.

METHODS

Frequencies of MBL2 allelic variants (B, C, D, and X) were estimated among 345 HIV-exposed children and 147 blood donors. AIDS-free time was evaluated for different MBL2 genotypes and MBL plasma levels. The median duration of follow-up was 96.5 months.

RESULTS

In the Argentinean population, gene frequencies of MBL2 variants were 18%, 15%, and 3% for the X, B, and D alleles, respectively, with no identified C allele. The haplotype XA/XA was associated with an 8-fold risk of acquiring HIV-1 (P= .054; odds ratio [OR], 8.11 [95% confidence interval {CI}, 0.96-67.86]) and almost a 3-fold risk of progression to pediatric AIDS (P= .026; OR, 2.81 [95% CI, 1.14-7.47]). We also found an independent positive correlation between the rate of AIDS progression and MBL plasma concentration (P= .008; OR, 1.28 [95% CI, 1.07-1.55]).

CONCLUSIONS

Our results demonstrate that homozygosity for the MBL2 promoter genotype XA/XA is an important genetic determinant of HIV-1 acquisition through vertical transmission and the pathogenesis of pediatric HIV/AIDS, via a mechanism that remains to be established.

General aspects of the genetics of SLE

The application of genetic techniques to the study of systemic lupus erythematosus (SLE) has identified candidate genes with diverse immunological function. There is a growing understanding that susceptibility to SLE is due to a complex interaction of multiple genes and environmental factors, and that many of these may be shared with other autoimmune diseases. In this first of a series of review articles we outline our current understanding of SLE genetics, in particular summarising the results of recent association studies.

Characterization of a polymorphism in the coding sequence of FCN3 resulting in a Ficolin-3 (Hakata antigen) deficiency state

Ficolin-3 (Hakata antigen or H-ficolin) is a soluble pattern recognition molecule in the lectin complement pathway. We speculated whether common genetic variations in the FCN3 gene contribute to deficiency of Ficolin-3. The FCN3 gene was sequenced in 237 healthy Danish Caucasians. The relevance of polymorphisms was assessed with antibodies against Ficolin-3 in a novel ELISA system and by production of recombinant Ficolin-3 variants. Ficolin-3 serum profiles were analyzed by SDS-PAGE and western blotting. Ficolin-3 serum concentration varied 10-fold (median, 24microg/ml; range, 3-54microg/ml). Out of several polymorphisms one FCN3+1637delC causing a reading frame shift and a distortion of the C-terminal end of the molecule with an allele frequency of 0.011 was particularly interesting. In individuals heterozygous for the FCN3+1637delC deletion lowered Ficolin-3 concentration was observed (P=0.025). SDS-PAGE and western blotting of serum revealed a weak band corresponding to the truncated molecule in addition to the normal Ficolin-3 pattern. Characterization of recombinant Ficolin-3 derived from FCN3+1637delC showed that in the homozygous situation this allelic variant would lead to Ficolin-3 deficiency. In conclusion an FCN3+1637delC deletion variant disrupting the possibility for pattern recognition was detected. Characterization of recombinant variant Ficolin-3 shows that homozygosity for the FCN3+1637delC deletion may lead to Ficolin-3 deficiency and may thus be the basis for a novel complement deficiency state.

Clinical and genetic risk factors for pneumonia in systemic lupus erythematosus

OBJECTIVE

To define the contribution of polymorphisms in genes encoding tumor necrosis factor (TNF), mannose-binding lectin (MBL), and Fcgamma receptor IIa (FCGR2A) as well as clinical factors, to the development of pneumonia in patients with systemic lupus erythematosus (SLE).

METHODS

We studied 282 SLE patients from a multiethnic cohort. Pneumonia events and clinical risk factors for pneumonia were identified through medical record review. Genotyping was performed for MBL (+223, +230, and +239), TNF (-308, -238, and +488), and FCGR2A (-131H/R) polymorphisms. Univariate analyses were performed to identify clinical and genetic risk factors for pneumonia. Covariates for multivariate analysis included sex, ethnicity, treatment with immunomodulators, and leukopenia.

RESULTS

Forty-two patients (15%) had at least 1 episode of pneumonia. Polymorphism of the TNF gene, particularly the -238A allele and a related haplotype, revealed the most striking and consistent association with pneumonia in univariate analyses. Results of multivariate analyses indicated an odds ratio (OR) for the TNF -238A allele of 3.5 (P = 0.007) and an OR for the related haplotype of 5.4 (P = 0.001). Male sex, treatment with immunomodulators, and leukopenia also influenced the risk of pneumonia.

CONCLUSION

These findings suggest that specific TNF variants may identify SLE patients who are at particularly high risk of developing pneumonia. Given the prevalence and excessive morbidity associated with pneumonia in SLE, these findings have clinical relevance and provide insight into the pathogenesis.

Complement activating soluble pattern recognition molecules with collagen-like regions, mannan-binding lectin, ficolins and associated proteins

Mannan-binding lectin (MBL), L-ficolin, M-ficolin and H-ficolin are all complement activating soluble pattern recognition molecules with recognition domains linked to collagen-like regions. All four may form complexes with four structurally related proteins, the three MBL-associated serine proteases (MASPs), MASP-1, MASP-2 and MASP-3, and a smaller MBL-associated protein (MAp19). The four recognition molecules recognize patterns of carbohydrate or acetyl-group containing ligands. After binding to the relevant targets all four are able to activate the complement system. We thus have a system where four different and/or overlapping patterns of microbial origin or patterns of altered-self may be recognized, but in all cases the signalling molecules, the MASPs, are shared. MASP-1 and MASP-3 are formed from one gene, MASP1/3, by alternative splicing generating two different mRNAs from a single primary transcript. Similarly MASP-2 and MAp19 are both generated from one gene, MASP-2/MAp19, by alternative splicing. A number of non-synonymous polymorphisms of the four recognition molecules and of the MASPs are known, and the implications of these alterations are being studied. The clinical impact of deficiencies will be discussed.

The role myeloid dendritic cells play in the pathogenesis of systemic lupus erythematosus

Dendritic cells (DC) play a pivotal role in the development of immune responses and the maintenance of peripheral tolerance. They continuously patrol tissues and sample antigens in search for the presence of inflammatory or pathogen-derived signals; they mature in accordance to signs prevalent in their environment and, by doing so, acquire certain features that will allow them to convey a precise message--either productive or regulatory--to the T cells they will encounter within regional lymph nodes. Evidence suggests that DC are involved in the pathogenesis of SLE. Their capacity to induce an antinuclear-oriented autoimmune response has been proven in animal models. Further, their maturation process is abnormal and their cytokine secretion and T cell stimulation is biased in patients with SLE. Lupus, however, is a problematic environment for their study and characterization. Sera from SLE patients contain several factors capable of inducing phenotypic and functional changes in DC. Thus, the abnormalities that have been reported may represent DC-intrinsic defects, a skewed phenotype due to an abnormal milieu, or a combination of both. In this review we discuss the available information in an attempt to reconcile these issues.

Mechanisms of disease: the complement system in renal injury--new ways of looking at an old foe

The fact that the complement system is activated during immune-complex glomerular disease has been known for nearly 50 years. Detection of complement deposition in the glomerulus using immunochemistry has become an important element of the histological analysis of renal biopsies, and is key to the diagnosis of many types of glomerulonephritis. In recent years it has become evident that complement activation is involved in the pathogenesis of other types of renal disease; complement activation is implicated in transplant injury, atypical hemolytic uremic syndrome and progressive tubulointerstitial fibrosis. Emergence of this evidence has provided insight into how these diseases develop, and has yielded useful diagnostic tools and potential targets for therapeutic intervention. Clinicians have, by using plasma-based therapies, unknowingly treated abnormalities of the complement system in renal patients for many years. Advances in antibody and protein technologies have led to the development of complement inhibitors that have been used in phase III clinical studies. More-specific agents and applications are likely to be developed over the coming years and are discussed in this Review.

The role of the mannose-binding lectin in innate immunity

The innate immune system, which includes mannose-binding lectin (MBL), recognizes a broad range of molecular patterns on a broad range of infectious agents and is able to distinguish them from self. MBL is a liver-derived serum protein and is secreted into the serum, where it can activate an immune response before the induction of antigen-specific immunity. Circumstantial evidence in human populations suggests that low serum levels of MBL predispose to infection. To analyze the role of MBL in vivo, we created MBL-null mice and challenged these mice with infection under various conditions. Our results suggest that MBL plays an important role as a first-line host defense against certain infectious agents. In addition, it is likely that MBL is a key regulator of inflammation beyond expected roles in the infection.

Deficiency of functional mannose-binding lectin is not associated with infections in patients with systemic lupus erythematosus

Infection imposes a serious burden on patients with systemic lupus erythematosus (SLE). The increased infection rate in SLE patients has been attributed in part to defects of immune defence. Recently, the lectin pathway of complement activation has also been suggested to play a role in the occurrence of infections in SLE. In previous studies, SLE patients homozygous for mannose-binding lectin (MBL) variant alleles were at an increased risk of acquiring serious infections in comparison with patients who were heterozygous or homozygous for the normal allele. This association suggests a correlation between functional MBL level and occurrence of infections in SLE patients. We therefore investigated the biological activity of MBL and its relationship with the occurrence of infections in patients with SLE. Demographic and clinical data were collected in 103 patients with SLE. Functional MBL serum levels and MBL-induced C4 deposition were measured by enzyme-linked immunosorbent assay using mannan as coat and an MBL- or C4b-specific monoclonal antibody. The complete MBL-dependent pathway activity was determined by using an assay that measures the complete MBL pathway activity in serum, starting with binding of MBL to mannan, and was detected with a specific monoclonal antibody against C5b-9. Charts were systematically reviewed to obtain information on documented infections since diagnosis of SLE. Major infections were defined as infections requiring hospital admission and intravenous administration of antibiotics. In total, 115 infections since diagnosis of lupus, including 42 major infections, were documented in the 103 SLE patients (mean age 41 ± 13 years, mean disease duration 7 ± 4 years). The percentage of SLE patients with severe MBL deficiency was similar to that in 100 healthy controls: 13% versus 14%, respectively. Although deposition of C4 to mannan and MBL pathway activity were reduced in 21% and 43% of 103 SLE patients, respectively, neither functional MBL serum levels nor MBL pathway activity was associated with infections or major infections in regression analyses. In conclusion, SLE patients frequently suffer from infections, but deficiency of functional MBL does not confer additional risk.

Infections in systemic lupus erythematosus: a prospective and controlled study of 110 patients

We decided to analyse the incidence and characteristics of infection in systemic lupus erythematosus (SLE) and determine the related risks factors. One-hundred and ten SLE patients and 220 controls were prospectively followed up over three years and all the infectious episodes were recorded. A case-control design was established to identify risk factors of infection. Thirty-nine SLE patients suffered at least one infection (36%) versus 53 controls (22%), RR = 1.63 (P < 0.05). The incidence of urinary infections, pneumonia and bacteraemia without known focus was significantly greater in SLE. E. coli was the chief isolated microorganism (21.3%). In the univariate analysis, nephritis, SLE activity, leucopenia, anti-dsDNA levels above 20 IU/mL, CH50 levels under 300 IU/mL, ever use of steroids, daily dose of prednisone higher than 10 mg and ever use of cyclophosphamide were significantly associated with infection. In the multivariate analysis, total serum complement levels below 300 UU/mL and a daily dose of prednisone above 20 mg during at least one month plus ever use of cyclophosphamide were found to be significant (P < 0.0001). We conclude that patients with SLE have an increased overall risk for infection and they are especially prone to develop urinary infection, pneumonia and bacteraemia without focus. Hypocomplementaemia represents an independent predictive factor for infection. It seems mandatory to closely follow up SLE patients with low complement levels and instruct them to report any suspicious sign of infection, especially in those receiving more than 20 mg/day of prednisone who have also been administered cyclophosphamide.

Autoimmunity to protective molecules: is it the perpetuum mobile (vicious cycle) of autoimmune rheumatic diseases?

Apoptotic defects and impaired clearance of cellular debris are considered key events in the development of autoimmunity, as they can contribute to autoantigen overload and might be involved in the initiation of an autoimmune response. The C1q protein and mannose-binding lectin are activators of the complement system. The pentraxins are a group of highly conserved proteins including the short pentraxins, C-reactive protein and serum amyloid P, and the long pentraxin family member, pentraxin 3, all of which are involved in innate immunity and in acute-phase responses. In addition to their role in innate immunity and inflammation, each of these proteins participates in the removal of damaged and apoptotic cells. In this article, we discuss the clinical significance of different levels of these proteins, their role in the induction of or protection against autoimmunity, and the presence of specific autoantibodies against them in various autoimmune diseases.

Infections in Systemic Connective Tissue Diseases: Systemic Lupus Erythematosus, Scleroderma, and Polymyositis/Dermatomyositis

In SLE, scleroderma, and PM/DM, infections are important causes of morbidity and mortality. This increased risk for developing infections is the result of immune abnormalities and of organ system manifestations associated with these diseases and their treatments. Common bacteria are responsible for most mild and lethal infections; however, opportunistic microorganisms cause death in some patients, particularly in those receiving high doses of corticosteroid and immunosuppressive therapy. Various viral and fungal infections also contribute to the morbidity and mortality associated with these diseases. Regardless of the cause of infections, adequate and prompt recognition and proper treatment of the infected patient are imperative. Patients who have these diseases, especially when receiving high doses of corticosteroids and immunosuppressive therapy, need to be monitored closely for these infections. This care and concern is necessary to ensure optimal patient outcomes, both in morbidity and mortality.

Mannose-binding lectin in innate immunity: past, present and future

The human collectin, mannose‐binding lectin (MBL), is an important protein of the humoral innate immune system. With multiple carbohydrate‐recognition domains, it is able to bind to sugar groups displayed on the surfaces of a wide range of microorganisms and thereby provide first‐line defence. Importantly, it also activates the complement system through a distinctive third pathway, independent of both antibody and the C1 complex. Three single point mutations in exon 1 of the expressed human MBL‐2 gene appear to impair the generation of functional oligomers. Such deficiencies of functional protein are common in certain populations, e.g. in sub‐Saharan Africa, but virtually absent in others, e.g. indigenous Australians. MBL disease association studies have been a fruitful area of research and implicate a role for MBL in infective, inflammatory and autoimmune disease processes. Overall, there appears to be a genetic balance in which individuals generally benefit from high levels of the protein. However, in certain situations, reduced levels of circulating MBL may be beneficial to the host and this may explain the persistence of the deleterious gene polymorphisms in many population groups.

Multiplex family?based study in systemic lupus erythematosus: association between the R620W polymorphism of PTPN22 and the Fc?RIIa (CD32A) R131 allele

A functional polymorphism in PTPN22, a gene encoding a phosphatase involved in T-cell signaling, has been associated with autoimmunity. We checked for the prevalence of the PTPN22 R620W polymorphism in multiplex families affected with systemic lupus erythematosus (SLE) and other autoimmune diseases. Its association with other polymorphisms in mannose binding lectin (MBL) and FcgammaRIIa (CD32A) genes was also studied. Deoxyribonucleic acid samples were obtained from 233 Spanish individuals who belonged to 21 families in which at least two members had been diagnosed with some autoimmune disease, mainly SLE. A healthy control population was also included (n= 129). Genotyping for the R620W single-nucleotide polymorphism (SNP) was performed by restriction fragment length polymorphism analysis of polymerase chain reaction products. Allele frequency for the T allele was slightly higher in the families with autoimmune disease, especially when considering the affected individuals (0.094 vs 0.062). Actually, 18.8% affected family members vs 11.6% controls had the polymorphism (P= 0.179). Nineteen percent of affected individuals had both the PTPN22 T and the CD32A R131 alleles, whereas only 8.5% unaffected relatives had both susceptibility alleles simultaneously [P= 0.031, odds ratios 2.508 (95% confidence interval 1.066-5.896)]. The tendency toward finding the T allele more frequently in members affected with some particular autoimmune disorder suggests that this SNP may confer susceptibility to autoimmunity. The fact that more affected than unaffected relatives carried both the T and the R131 alleles simultaneously leads us to think about the existence of a combinatorial effect between genes that could help define individuals prone to autoimmune diseases.

Unraveling the genetics of systemic lupus erythematosus

The capacity to locate polymorphisms on a virtually complete map of the human genome coupled with the ability to accurately evaluate large numbers (by historical standards) of genetic markers has led to gene identification in complex diseases, such as systemic lupus erythematosus (SLE or lupus). While this is a phenotype with enormous clinical variation, the twin studies and the observed familial aggregation, along with the genetic effects now known, suggest a strong genetic component. Unlike type 1 diabetes, lupus genetics is not dominated by the powerful effect of a single locus. Instead, there are at least six known genetic association effects in lupus of smaller magnitude (odds ratio <2), and at least 17 robust linkages (established and arguably confirmed independently) defining potentially responsible genes that largely remain to be discovered. The more convincing genetic associations include the human leukocyte antigen region (with multiple genes), C1q, PTPN22, PDCD1, Fc receptor-like 3, FcgammaRIIA, FcgammaRIIIA, interferon regulatory factor 5, and others. How they contribute to disease risk remains yet to be clarified, beyond the obvious speculation derived from what has previously been learned about these genes. Certainly, they are expected to contribute to lupus risk independently and in combination with each other, with genes not yet identified, and with the environment. A substantial number of genes (>10) are expected to be identified to contribute to lupus or in its many subsets defined by clinical and laboratory features.

Complement proteins C1q and MBL are pattern recognition molecules that signal immediate and long-term protective immune functions

C1q and mannose binding lectin, members of the "defense collagen" family, are pattern recognition molecules that can trigger rapid enhanced phagocytosis resulting in efficient containment of pathogens or clearance of cellular debris, apoptotic cells and immune complexes. In addition, interaction of C1q and mannose binding lectin with the phagocyte alters subsequent phagocyte cytokine synthesis, and thus may have important implications in directing acute inflammation as well as long-term protective immunity. The importance of the role of defense collagens in phagocytosis of apoptotic cells is highlighted by studies in vivo of mice deficient in C1q, pulmonary surfactant D and mannose binding lectin in which there is delayed clearance of apoptotic cells. Indeed, deficiency of C1q is a risk factor for the development of autoimmunity in both humans and mice, consistent with the hypothesis that inefficient clearance of apoptotic cells results in release of autoantigens and contributes to the pathology associated with autoimmune diseases such as systemic lupus erythematosus. Further understanding of the importance of C1q and mannose binding lectin in the clearance of apoptotic cells and regulation of cytokine synthesis and identification of the receptors implicated in mediating these processes should provide novel targets for therapeutic intervention in the control and manipulation of the immune response in terms of both host defense against infectious disease and tissue repair and remodeling.

Chemotherapy-related infections in patients with multiple myeloma: associations with mannan-binding lectin genotypes

OBJECTIVES

To study a possible association between mannan-binding lectin genotypes and severe infections in patients with multiple myeloma receiving moderate strength induction chemotherapy.

METHODS

Chemotherapy-related infections were identified retrospectively using clinical records and database files. Mannan-binding lectin genotypes were identified with polymerase chain reaction on stored samples of stem cells or formalin-fixed paraffin-embedded bone marrow biopsies.

RESULTS

We included 138 myeloma patients. In five patients, data were incomplete, and 133 patients were analysed. Eighty-eight patients were homozygous for wild-type MBL2 (AA) and forty-five patients were heterozygous or homozygous for variant genotypes (AO/OO). A total of 390 chemotherapy cycles were reviewed. Common Toxicity Criteria grades 3 and 4 infections in general were seen in relation to 104 cycles and were not more common in patient with variant MBL2 (P = 0.90). Septicaemia was seen after 10% of chemotherapy cycles in AA patients vs. 15% in AO/OO patients (P = 0.15). In multi-variate analyses, we found indication of a reduced risk of septicaemia in AA patients [OR 0.27 (0.08-0.90), P = 0.03], after first chemotherapy cycle, but reduction of the risk including all cycles was not significant. A similar trend was seen for grades 3 and 4 infections in general.

CONCLUSIONS

During induction chemotherapy in patients with multiple myeloma, a general protective effect of wild-type MBL2 against chemotherapy-related infections was not apparent in this study. However, we found indications of a reduced occurrence of septicaemia in patients with wild-type compared with variant MBL2. Further studies in larger cohorts of patients are relevant.

Mechanisms of Disease: the complement system and the pathogenesis of systemic lupus erythematosus

Complement activation is common in patients with systemic lupus erythematosus (SLE), resulting in hypocomplementemia and deposition of complement at sites of tissue damage. The availability of mice with specific deficiencies of components of the complement system has provided new insights into the mechanisms by which complement might be involved in autoimmunity and tissue injury in SLE. In humans, deficiencies of early components of the classical complement pathway are strongly associated with SLE. Mice lacking C1q or C4 are also predisposed to autoimmunity, which is associated with the failure of normal clearance of apoptotic cells bearing on their surfaces many of the autoantigens involved in SLE. Antiphospholipid syndrome is common in patients with SLE and studies in an animal model of fetal loss caused by antiphospholipid syndrome have shown that injury is dependent on activation of complement with subsequent neutrophil influx and synthesis of tumor necrosis factor. Insights from animal models might enable the design of more rational therapeutic approaches for manipulating the complement system in human SLE.

Mannose-Binding Lectin: Clinical Implications for Infection, Transplantation, and Autoimmunity

Mannose-binding lectin (MBL) is a recognition molecule of the lectin pathway of complement and a key component of innate immunity. MBL variant alleles have been described in the coding region of the MBL gene, which are associated with low MBL serum concentration and impaired MBL structure and function. Both high and low serum levels of functional MBL have been associated with a variety of diseases and disease complications. Functioning as double-edged sword, low MBL serum levels have been shown to enhance the risk for infections. On the other hand, high MBL serum levels and high MBL activity have been associated with inflammatory diseases, transplant rejection, and diabetic nephropathy. Underscoring the Jekyll-and-Hyde character of MBL, both high and low serum MBL levels are associated with several aspects of autoimmune diseases. This review provides a general outline of the genetic and molecular characteristics of MBL and discusses MBL-disease association and its consequence in infection, transplantation, and autoimmunity.

Clinical manifestations of mannan-binding lectin deficiency

Mannan-binding lectin (MBL) is a plasma protein of the innate immune system with the ability to initiate antimicrobial and inflammatory actions. MBL deficiency is common. More than 10% of the general population may, depending on definition, be classified as MBL deficient, underlining the redundancy of the immune system. Ongoing research attempt to illuminate at which conditions MBL deficiency may lead to disease. With examples, this review illustrates the diversity of results obtained so far.

The association between inherited cytokine polymorphisms and cerebral palsy

OBJECTIVE

The purpose of this study was to investigate associations between inherited cytokine polymorphisms and cerebral palsy.

STUDY DESIGN

This was a case-control study that used DNA from the newborn infant screening cards of 443 white infants with cerebral palsy and 883 white control infants to test for the following cytokine polymorphisms: tumor necrosis factor-alpha-308, mannose-binding lectin-221, and 3 polymorphisms in exon-1 of the mannose-binding lectin gene at codon-52, -54, and -57.

RESULTS

At all gestational ages mannose-binding lectin codon-54 increased the risk of the development of diplegia (homozygous or heterozygous odds ratio, 1.55; 95% CI, 1.03-2.32). For babies who were born at term, the risk of the development of quadriplegia was associated with heterozygous tumor necrosis factor-alpha (odds ratio, 1.82; 95% CI, 1.04-3.15), and mannose-binding lectin codon-54 was associated with diplegia (homozygous or heterozygous odds ratio, 2.12; 95% CI, 1.10-4.05). The presence of any polymorphism in mannose-binding lectin exon-1 at term approximately doubled the risk of the development of diplegia (odds ratio, 1.94; 95% CI, 1.05-3.62). Homozygous or heterozygous tumor necrosis factor-alpha was associated with hemiplegia for babies who were born at <32 weeks of gestation (odds ratio, 2.38; 95% CI, 1.02-5.58). Overall, the presence of any cytokine polymorphism was associated with cerebral palsy (odds ratio, 1.37; 95% CI, 1.02-1.84).

CONCLUSION

Carriage of polymorphisms in the tumor necrosis factor-alpha and mannose-binding lectin genes are associated with an increased risk of cerebral palsy.