Association of variants of the gene for mannose-binding lectin with susceptibility to meningococcal disease. Meningococcal Research Group

Single nucleotide polymorphisms in genes of circulatory homeostasis in surviving pediatric intensive care patients with meningococcal infection

OBJECTIVE

In the course of a meningococcal infection, invasive and severe disease occurs in a restricted number of individuals. The predominant mechanism of death in case of meningococcal septic shock is circulatory failure. Inotropic requirements between patients vary widely. We investigated whether polymorphisms in genes regulating the hemodynamic response influence the amount of inotropics required or the susceptibility to severe meningococcal disease.

DESIGN

Retrospective case control study.

SETTING

Single-center pediatric intensive care unit (PICU).

PATIENTS

Fifty-six cases (all consecutive patients admitted to the PICU between 1993 and 2001 with a proven meningococcal infection) and 136 controls. Patients were divided into two groups according to their inotropic requirements.

INTERVENTION

DNA analysis was performed to determine the polymorphisms of the beta-adrenergic receptor gene-1, beta-adrenergic receptor gene-2, alpha-adducin, angiotensin converting enzyme, and angiotensin II type-1 receptor-1 genes.

RESULTS

For the alpha-adducin gene a significant difference of the genotype distribution was found between the cases and controls. The odds ratio for admission to the PICU with meningococcal sepsis with or without meningitis, for carriers of the variant allele (Gly460Trp or Trp460Trp) was 2.1 (95% confidence interval 1.11-4.04; p < 0.02). Cases, homozygote for the wild-type allele of the beta-1 adrenergic receptor at locus 389, were more likely to have a low pediatric risk of mortality score on admission (odds ratio 3.6, 95% confidence interval 1.11-11.76). No difference was found in the distribution of the beta-adrenergic receptor gene-1, beta-adrenergic receptor gene-2, angiotensin converting enzyme, and angiotensin II type-1 receptor-1 polymorphisms between the two groups of patients or between cases and controls.

CONCLUSIONS

Among patients admitted to the PICU with a meningococcal infection, the variant allele of the alpha-adducin gene was more prevalent compared with controls. Patients with the variant allele of the beta-adrenergic receptor gene-1 at locus 389 were more likely to have a high pediatric risk of mortality score on admission. The mechanism and clinical relevance of these findings is unclear.

Low serum mannose-binding lectin level increases the risk of death due to pneumococcal infection

BACKGROUND

Previous studies have shown associations between low mannose-binding lectin (MBL) level or variant MBL2 genotype and sepsis susceptibility. However, MBL deficiency has not been rigorously defined, and associations with sepsis outcomes have not been subjected to multivariable analysis.

METHODS

We reanalyzed MBL results in a large cohort with use of individual data from 4 studies involving a total of 1642 healthy control subjects and systematically defined a reliable deficiency cutoff. Subsequently, data were reassessed to extend previous MBL and sepsis associations, with adjustment for known outcome predictors. We reanalyzed individual data from 675 patients from 5 adult studies and 1 pediatric study of MBL and severe bacterial infection.

RESULTS

XA/O and O/O MBL2 genotypes had the lowest median MBL concentrations. Receiver operating characteristic analysis revealed that an MBL cutoff value of 0.5 microg/mL was a reliable predictor of low-producing MBL2 genotypes (sensitivity, 82%; specificity, 82%; negative predictive value, 98%). MBL deficiency was associated with increased likelihood of death among patients with severe bacterial infection (odds ratio, 2.11; 95% confidence interval, 1.30-3.43). In intensive care unit-based studies, there was a trend toward increased risk of death among MBL-deficient patients (odds ratio, 1.58; 95% confidence interval, 0.90-2.77) after adjustment for Acute Physiology and Chronic Health Enquiry II score. The risk of death was increased among MBL-deficient patients with Streptococcus pneumoniae infection (odds ratio, 5.62; 95% confidence interval, 1.27-24.92) after adjustment for bacteremia, comorbidities, and age.

CONCLUSIONS

We defined a serum level for MBL deficiency that can be used with confidence in future studies of MBL disease associations. The risk of death was increased among MBL-deficient patients with severe pneumococcal infection, highlighting the pathogenic significance of this innate immune defence protein.

An age-dependent association of mannose-binding lectin-2 genetic variants on HIV-1-related disease in children

BACKGROUND

Mannose-binding lectin (MBL) is part of the lectin pathway of complement activation against various pathogens; however, its role in innate immune responses against HIV-1 infection in children is unknown.

OBJECTIVE

This study evaluated the effects of mannose-binding lectin-2 (MBL2) alleles on HIV-1 disease progression and central nervous system (CNS) impairment in children.

METHODS

A cohort of 1037 HIV-1-infected children enrolled in Pediatrics AIDS Clinical Trial Group protocols P152 and P300 before the availability of effective antiretroviral therapy was genotyped for MBL2 and evaluated for disease progression.

RESULTS

Children with the homozygous variant MBL2-O/O genotype were more likely to experience rapid disease progression and CNS impairment than those with the wild-type AA genotype. The effects were predominantly observed in children younger than 2 years. In unadjusted Cox proportional hazards models, children younger than 2 years with MBL2-O/O experienced more rapid disease progression (O/O vs AA: relative hazard [RH], 1.54; 95% CI, 1.07-2.22; P = .02; O/O vs A/O: RH, 2.28; 95% CI, 1.09-4.79; P = .029). Similarly, children with MBL2-O/O were more likely to experience rapid progression to CNS impairment (O/O vs A/A: RH, 2.78; 95% CI, 1.06-2.69, P = .027; O/O vs A/O: RH, 1.69; 95% CI, 1.07-7.21; P = .035). The effects remained significant after adjustment for CD4(+) lymphocyte count, plasma HIV-1 RNA, and other genotypes.

CONCLUSIONS

MBL2-O/O genotypes, which result in lower expression of MBL, are associated with more rapid HIV-1-related disease progression, including CNS impairment, predominantly in children younger than 2 years. These data suggest that MBL2 variants are associated with altered HIV-1 disease progression, particularly in young children.

Mannose-binding lectin gene polymorphic variants predispose to the development of bronchopulmonary complications but have no influence on other clinical and laboratory symptoms or signs of common variable immunodeficiency

Mannose-binding lectin (MBL), activating protein of the lectin pathway of the complement system, is an important component of the non-specific immune response. MBL2 gene polymorphisms, both in the coding and promoter regions, lead to low or deficient serum MBL levels. Low serum MBL levels were shown to be associated with serious infectious complications, mainly in patients in whom other non-specific immune system barriers were disturbed (granulocytopenia, cystic fibrosis). We have analysed two promoter (-550 and -221) and three exon (codons 52, 54 and 57) MBL2 polymorphisms in a total of 94 patients with common variable immunodeficiency (CVID) from two immunodeficiency centres. Low-producing genotypes were associated with the presence of bronchiectasis (P = 0.009), lung fibrosis (P = 0.037) and also with respiratory insufficiency (P = 0.029). We could not demonstrate any association of MBL deficiency with age at onset of clinical symptoms, age at diagnosis, the number of pneumonias before diagnosis or serum immunoglobulin (Ig)G, IgA and IgM levels before initiation of Ig treatment. No association with emphysema development was observed, such as with lung function test abnormalities. No effect of MBL2 genotypes on the presence of diarrhoea, granuloma formation, lymphadenopathy, splenomegaly, frequency of respiratory tract infection or the number of antibiotic courses of the patients was observed. Our study suggests that low MBL-producing genotypes predispose to bronchiectasis formation, and also fibrosis and respiratory insufficiency development, but have no effect on other complications in CVID patients.

Genetic approach to pediatric septic shock

Septic shock is a complex and heterogeneous clinical syndrome, triggered by infection, and having significant morbidity and mortality in children. Emerging data indicate that the genetic make-up of the pediatric host may have a strong influence on the development and outcome of septic shock in children. Herein, we review this broad topic by focusing on pediatric-specific data (both recent and historical), as well as the broad topics of SNPs, genome-wide association studies and epigenetics. The historical and emerging data strongly suggest that a genetics-based perspective will need to be considered in future investigations and strategies aimed at improving the outcome of children with septic shock.

Mannose-binding lectin in HIV infection

Infection with HIV represents a significant global health problem, with high infection rates and high mortality worldwide. Treatment with antiretroviral therapy is inaccessible to many patients and efficacy is limited by development of resistance and side effects. The interactions of HIV with the human immune system, both innate and humoral, are complex and complicated by the profound ability of the virus to disable the host immune response. Mannose-binding lectin, a component of the innate immune system, has been demonstrated to play a role in host-virus interactions. This protein may have a key role in determining host susceptibility to infection, pathogenesis and progression of disease, and may contribute to the extensive variability of host response to infection. Further understanding and manipulation of the mannose-binding lectin response may represent a target for immunomodulation in HIV infection, which may, in conjunction with highly active antiretroviral therapy, allow development of a novel therapeutic approach to HIV infection.

Mannose-binding lectin haplotypes influence Brucella abortus infection in the water buffalo (Bubalus bubalis)

A case-control study established that the haplotype pair HYA/HYA at the MBL (mannose binding lectin) locus of water buffalo is associated with resistance to Brucella abortus infection (P < 10(-7)) and the haplotype pairs LYD/LYD with susceptibility to the same pathogen (P < 10(-7)). The subjects included in the present study were tested twice-at a 1-month interval-for the presence of anti-B. abortus antibodies in the serum by agglutination, complement fixation and flow cytometry. Cases (335 subjects) included animals consistently positive to all these tests; controls (335 subjects) comprised animals exposed yet negative by the same tests. The serum from genetically resistant subjects displayed in vitro significantly higher antibacterial activity compared to the serum from genetically susceptible subjects, lending biological significance to the results from the association study. Inhibition of the antibacterial activity following heat treatment of the serum, addition of specific MBL inhibitors (EDTA, mannose, N-acetyl-D: -glucosamine) or anti-human MBL antiserum provide convincing evidence that the antibacterial activity present in the serum results from the interaction between MBL and B. abortus. A replication study (comprising 100 cases and 100 controls) confirmed the results from the original study.

Mannose-binding lectin variant associated with severe malaria in young African children

Mannose-binding lectin (MBL) is a serum protein which initiates innate immune responses to microbial pathogens by binding to non-self surface oligosaccharides. MBL deficiency is the most common congenital immunodeficiency of human and has been shown to predispose to infections, particularly in children and immune compromised. In a matched case-control study among 870 Ghanaian children, we examined the influence of six polymorphisms of the MBL2 gene on Plasmodium falciparum infection and severe malaria. A missense mutation resulting in low MBL activity (MBL2*C) was found in 35% of healthy controls, but in 42% of asymptomatically infected children (P=0.01), and in 46% of patients with severe malaria (P=0.007). Heterozygosity for MBL2*C was associated with increased odds of infection (odds ratio (OR), 1.6; 95% confidence interval (CI), 1.1-2.1), severe malaria (OR, 1.7; 95% CI, 1.2-2.4), and of severe anemia in particular (OR, 2.3; 95% CI, 1.4-3.8). The population attributable fraction of severe malaria cases attributable to MBL2*C heterozygosity was 17%. Our results suggest that the MBL pathway of the complement system is a critical determinant of both, susceptibility to P. falciparum infection and manifestation of severe malaria, particularly in young children in whom specific immune responses are weak or absent.

Association of polymorphisms in the mannose-binding lectin gene and pulmonary morbidity in preterm infants

Deficiency in the collectin mannose-binding lectin (MBL) increases the risk for pulmonary and systemic infections and its complications in children and adults. The aim of this prospective cohort study was to determine the genetic association of sequence variations within the MBL gene with systemic infections and pulmonary short- and long-term complications in preterm infants below 32 weeks gestational age (GA). Three single-nucleotide polymorphisms (SNPs) in the coding region and one SNP in the promotor region of MBL2 were genotyped by direct sequencing and with sequence-specific probes in 284 newborn infants <32 weeks GA. Clinical variables were comprehensively monitored. An association was found between two SNPs and the development of bronchopulmonary dysplasia (BPD), defined as persistent oxygen requirement at 36 weeks postmenstrual age, adjusting for covariates GA, grade of respiratory distress syndrome and days on mechanical ventilation (rs1800450 (exon 1 at codon 54, B variant): odds ratio dominant model (OR)=3.59, 95% confidence interval (CI)=1.62-7.98; rs7096206 (-221, X variant): OR=2.40, 95% CI=1.16-4.96). Haplotype analyses confirmed the association to BPD, and a single haplotype (frequency 56%) including all SNPs in their wild-type form showed a negative association with the development of BPD. We detected no association between the MBL gene variations and the development of early-onset infections or further pulmonary complications. Frequent variants of the MBL gene, leading to low MBL concentrations, are associated with the diagnosis of BPD in preterm infants. This provides a basis for potential therapeutic options and further genetic and proteomic analysis of the function of MBL in the resistance against pulmonary long-term complications in preterm infants.

Meningococcal disease in a kidney transplant recipient with mannose-binding lectin deficiency

We describe the case of a kidney transplant recipient who developed meningococcemia, without meningeal signs, 2 months after transplantation. Plasma levels of complement components C3, C4, and CH 50 were within the normal range. However, using a method to screen for the functional activity of all 3 pathways of complement, no activation via the mannose-binding lectin (MBL) pathway could be detected (0%). A subsequent quantification of MBL pathway components revealed normal levels of MASP 2 but undetectable amounts of MBL. To our knowledge, this is the first report of meningococcal disease after organ transplantation in a patient with MBL deficiency.

MBL2 genetic polymorphisms in Italian children with adenotonsillar hypertrophy

We investigated the role of the polymorphisms in the first exon of MBL2 gene in the susceptibility to recurrent tonsillitis in a selected group of Italian children and healthy controls. Significant difference has been observed in MBL2 genotype and allelic frequencies between children with recurrent tonsillitis and healthy controls matched for sex and age. Children characterized by a "low MBL" producer genotype, namely 00, are more prone to recurrent tonsillitis when compared to the healthy controls. To our knowledge this is the first report on the role of MBL2 polymorphisms in adenotonsillar hypertrophy and our results shown that presence of MBL2 00 genotype could be used as a prognostic marker in subjects with adenotonsillar hypertrophy.

Epidemic meningitis, meningococcaemia, and Neisseria meningitidis

Meningococcus, an obligate human bacterial pathogen, remains a worldwide and devastating cause of epidemic meningitis and sepsis. However, advances have been made in our understanding of meningococcal biology and pathogenesis, global epidemiology, transmission and carriage, host susceptibility, pathophysiology, and clinical presentations. Approaches to diagnosis, treatment, and chemoprophylaxis are now in use on the basis of these advances. Importantly, the next generation of meningococcal conjugate vaccines for serogroups A, C, Y, W-135, and broadly effective serogroup B vaccines are on the horizon, which could eliminate the organism as a major threat to human health in industrialised countries in the next decade. The crucial challenge will be effective introduction of new meningococcal vaccines into developing countries, especially in sub-Saharan Africa, where they are urgently needed.

Association of polymorphisms in the first exon of mannose binding lectin gene (MBL2) in Brazilian patients with HCV infection

In our study we investigated the role of the polymorphisms in the first exon of MBL2 gene in the susceptibility to HCV infection and disease progression in a Northeastern Brazilian population. One hundred and eleven patients seen at the Gastroenterology Service of the Oswaldo Cruz Hospital of the University of Pernambuco were included in this study. A total of 165 unexposed, uninfected individuals matched for place of origin were employed as healthy controls. MBL2 genotyping was performed by using a melting temperature assay. The 0 allele was significantly more frequent in the HCV positive group than the healthy controls (34% vs. 20%, p<0.01, respectively) and was associated to an increased risk of HCV-1 infection (O.R.=2.1; C.I. 1.41-3.19). Also genotypes frequencies were significantly different in HCV positive subjects when compared to healthy controls with the 00 and A0 genotypes being significantly overrepresented in HCV infected subject (15% and 37%, respectively) as compared to healthy subjects (6% and 27%, respectively, p<0.01 ) Allele and genotypes frequencies were also evaluated in HCV infected subjects according to their response to pegylated-INFalpha/riboviron therapy. There was a trend for HCV positive responders vs. non-responders to be 0 allele positive and a similar trend was observed for the MBL2 A0 and 00 genotypes, but neither of these reached statistical significance. Our findings indicate that MBL might represent an important antiviral molecule having a protective role in the first stages of HCV infection, as shown by the increased frequency of wild-type alleles in control population as compared to the infected group.

Mannan-binding lectin is a determinant of survival in infective endocarditis

Mannan-binding lectin (MBL) is a collectin plasma protein activating the lectin pathway of the complement system, enhancing opsonophagocytosis and modulating the cytokine response to inflammation. Deficiency of MBL, caused by structural mutations or promoter polymorphisms in the MBL2 gene, has been associated with increased susceptibility to infection and autoimmune disease. Thus, as infective endocarditis remains a severe disease requiring intensive and long-term treatment with antibiotics, we examined whether there was an association between MBL and clinical outcome in 39 well-characterized patients with infective endocarditis. Five patients (13%) had MBL concentrations < 100 microg/l and were considered MBL-deficient. This proportion was similar to that in a healthy control group of blood donors. Mortality 3 months after diagnosis was 20% in patients with MBL-deficiency and 9% in patients with normal MBL. The 5-year mortality was 80% and 25%, respectively. MBL-deficiency was on univariate survival statistics associated with significantly higher mortality on follow-up (P=0 x 03). In conclusion, this is the first report of an association between MBL-deficiency and survival in infective endocarditis. The present observation is important, as replacement therapy in MBL-deficient patients is possible. For certain high-risk subgroups, it opens new perspectives for improvement of treatment and outcome in infective endocarditis.

Low mannose-binding lectin complement activation function is associated with predisposition to Legionnaires' disease

Innate immune system deficiency may predispose to severe infections such as Legionnaires' disease. We have investigated the role of mannose-binding lectin (MBL) deficiency in the Melbourne Aquarium Legionnaires' disease outbreak. Serum samples from patients and controls that were exposed but shown to be uninfected from the Melbourne Aquarium Legionnaires' disease outbreak were tested for MBL function (C4 deposition) and level (mannan-binding). MBL function was lower in Legionnaires' disease cases than in age- and sex-matched uninfected, exposed controls. The frequency of MBL deficiency with C4 deposition < 0.2 U/microl was significantly higher in Legionnaires' disease cases than in controls. This also applied to Legionnaires' disease cases requiring hospital care. There was no difference in MBL mannan-binding levels between Legionnaires' disease patients and controls. There was no significant interval change in MBL function or level after a mean of 46 days. MBL complement activation functional deficiency appears to predispose to Legionnaires' disease.

Interactions between Neisseria meningitidis and the complement system

Meningococcal infection remains a worldwide health problem, and understanding the mechanisms by which Neisseria meningitidis evades host innate and acquired immunity is crucial. The complement system is vital for protecting individuals against N. meningitidis. However, this pathogen has evolved several mechanisms to avoid killing by human complement. Bacterial structures such as polysaccharide capsule and those which mimic or bind host molecules function to prevent complement-mediated lysis and phagocytosis. This review provides an update on the recent findings on the diverse mechanisms by which N. meningitidis avoids complement-mediated killing, and how polymorphisms in genes encoding human complement proteins affect susceptibility to this important human pathogen.

Conquering the meningococcus

Since the first outbreaks of meningococcal meningitis were first described in Geneva in 1804 and in New England in 1806, and since the discovery of the causative agent by Weichselbaum in 1887 and the beginning of epidemics of meningococcal meningitis in the sub-Saharan Africa approximately 100 years ago, Neisseria meningitidis has been recognized as the cause worldwide of epidemic meningitis and meningococcemia. The massive epidemic outbreaks in sub-Saharan Africa in the 1990's, the emergence since 1995 of serogroups Y, W-135 and X and the prolonged outbreak of serogroup B meningococcal disease in New Zealand over the last decade serve to remind us of the continued potential of the meningococcus to cause global morbidity and mortality. This report reviews new discoveries impacting prevention and future prospects for conquering the meningococcus as a human pathogen.

Age-dependent association of human mannose-binding lectin mutations with susceptibility to invasive meningococcal disease in childhood

BACKGROUND

Mannose-binding lectin (MBL) is an important factor of the innate immune system, and MBL-initiated complement activation is an important early defense mechanism against various bacterial infections, including invasive meningococcal disease.

METHODS

In a pediatric cohort (ages 2-215 months) with invasive meningococcal disease, we investigated the overall and age-stratified frequency of 3 MBL exon 1 variations (C154T, G161A, G170A), previously shown to result in markedly decreased MBL plasma concentrations, by allele specific fluorescent hybridization probe real-time PCR assays and direct sequencing. Healthy age-matched volunteers with the same ethnic background and no history of meningococcal disease served as a control group.

RESULTS

The overall frequency of a MBL exon 1 variant genotype was significantly higher in patients than in controls (31.8% vs. 8.2%, P < 0.001). In the patient group with disease onset less than 24 months of age, the prevalence of MBL structural variant genotype was further increased (39.3%; P < 0.001) and most pronounced in children with disease onset less than 12 months of age (57.1%; P < 0.001) when compared with healthy controls. Analysis of clinical severity and outcome revealed no significant difference between patients with wild-type and mutant alleles.

CONCLUSIONS

Our data suggest that MBL exon 1 structural variants are significantly associated with susceptibility to childhood meningococcal disease in an age-dependent manner.

Genetic association studies in VLBW infants exemplifying susceptibility to sepsis--recent findings and implications for future research

CONTEXT

In recent years, tremendous effort has been carried out to study the genetic basis of susceptibility to development, progression and severity of complex diseases and response to therapy. The ultimate goal of these investigations is to find new tools for prevention and treatment of these complex diseases, such as sepsis in very-low-birth-weight (VLBW) infants. VLBW cohorts have a restricted clinical risk profile for the development of sepsis including immaturity of immune functions and antenatal/perinatal risk factors but also a significant event rate of sepsis within a short period of observational time. Therefore, prospective VLBW cohorts are advantageous for the investigation of candidate genetic risk factors of sepsis compared to adult cohorts. Furthermore, environmental factors are much better documented and highly controlled for VLBW infants in a standardized NICU setting compared to adult cohorts which are influenced by a variety of environmental risk factors, e.g. habits and comorbidities.

OBJECTIVE

The aim of this review is to discuss the value and limitations of genetic association studies in VLBW infant cohorts exemplifying recent findings for genetic susceptibility to neonatal sepsis.

DATA SOURCE

Published Medline articles reporting on studies of associations between genetic polymorphisms, neonatal sepsis and septic shock in VLBW infants.

CONCLUSIONS

Up-to-date, the classical approach to investigate the genetic component of susceptibility to sepsis in VLBW infants by means of twin and concordance studies has not been implemented yet. Regarding the interpretation of data from current genetic association studies, one should be aware of significant differences in cohort size, study design and definition of cases, controls and clinical end points. Furthermore, the contribution of genetic variants to susceptibility to sepsis may be specifically influenced by the immaturity of the immune response in VLBW infants, the selectivity of responsiveness to certain pathogens and the genotopyic/phenotypic variability of pathogens. We provide implications for the conduct and evaluation of future association studies with particular reference to methodological quality standards.

Association Between Mannose-Binding Lectin Deficiency and Cytomegalovirus Infection After Kidney Transplantation

Mannose-binding lectin (MBL) deficiency has been suggested as a risk factor for certain viral infections. However, there is no data about the possible association between MBL deficiency and cytomegalovirus (CMV) infection, especially after organ transplantation. We measured plasma MBL levels in 16 kidney transplant recipients with high-risk CMV serostatus (donor-positive/recipient-negative). MBL deficiency was diagnosed if MBL levels were <500 ng/mL. Of these 16 patients, seven developed CMV disease, four developed asymptomatic CMV infection, and in five patients CMV replication was not detected. Overall, 9 of 16 patients (56%) had MBL deficiency: five of seven (71%) patients with CMV disease, four of four (100%) patients with asymptomatic CMV infection, and zero of five (0%) patients without CMV infection (P=0.005; CMV infection/disease versus no infection). MBL deficiency may be a significant risk factor for the development of CMV infection in kidney transplant recipients, suggesting a role for innate immunity in the control of CMV infection after organ transplantation.

Polymorphisms in the mannose binding lectin-2 gene and acute respiratory distress syndrome

OBJECTIVE

The variant alleles in the mannose binding lectin-2 (MBL-2) gene have been associated with MBL deficiency and increased susceptibility to sepsis. We postulate that the variant MBL-2 genotypes are associated with increased susceptibility to and mortality in acute respiratory distress syndrome (ARDS).

DESIGN

Nested case-control study.

SETTING

Tertiary academic medical center.

PATIENTS

Two hundred and twelve Caucasians with ARDS and 442 controls genotyped for the variant X, D, B, and C alleles of codon -221, 52, 54, and 57, respectively.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Patients homozygous for the variant codon 54B allele (54BB) had worse severity of illness on admission (p = .007), greater likelihood of septic shock (p = .04), and increased odds of ARDS (adjusted odds ratio, 6.7; 95% confidence interval, 1.5-31) when compared with heterozygotes and homozygotes for the wild-type allele. This association with ARDS was especially strong among the 311 patients with septic shock (adjusted odds ratio, 12.0; 95% confidence interval, 1.9-74). Among the patients with ARDS, the 54BB genotype was associated with more daily organ dysfunction (p = .01) and higher mortality (adjusted hazard rate, 4.0; 95% confidence interval, 1.6-10). Development of ARDS and outcomes in ARDS did not vary significantly with variant alleles of codon -221, 52, and 57, but the power to detect an effect was limited secondary to the low allele frequencies.

CONCLUSIONS

The MBL-2 codon 54BB genotype may be important in ARDS susceptibility and outcome. Additional studies are needed to confirm these findings in other populations.

Innate immunity: toll-like receptors and some more. A brief history, basic organization and relevance for the human newborn

The discovery of Toll-like receptors (TLRs) as essential components of the innate immune system has greatly advanced our knowledge and understanding of immune responses to infection and how these are regulated. Innate immunity in general and TLRs in particular play a crucial role in the front line of host defenses against microbes, but also are a key element in the proper functioning of the immune system at large in vertebrate animals. The innate immune system has been identified as a collection of factors, both cell-associated and cell-free, that comprises an impressively effective and well-organized system that is capable of immediate recognition of a whole array of microbes and microbial components. The cell-bound TLRs fulfill a central role in the process from pathogen recognition to activation of adaptive immunity. From the cell-free factors the plasma protein mannose-binding lectin (MBL) has been studied most extensively. Associations have already been documented between TLR polymorphisms in man and TLR deficiency in animals and an increased susceptibility to infection. The effect of MBL on infectious disease susceptibility only seems to emerge when host defenses are compromised by a severe underlying condition. The functional state of the various components of innate immunity at birth is largely unknown and only recently a number of studies have assessed this feature of the innate immune system. In addition, for the human newborn the innate immune system may have a broader significance; it may well be the key system determining the course of inflammatory events associated with premature birth, a notion that is emphasized by the recently described association between TLR polymorphisms and prematurity. However, there are still many open questions, particularly about the exact relation between individual TLRs and infectious disease susceptibility and how TLRs cooperate in resistance to infection and in initiating adaptive immune responses. With regard to the human newborn, the most relevant question that needs to be resolved is the precise role of innate immunity in the pathogenesis of prematurity.

Low mannose-binding lectin function is associated with sepsis in adult patients

Mannose-binding lectin (MBL) is an innate immune system pattern recognition molecule that kills a wide range of pathogens via the lectin complement pathway. MBL deficiency is associated with severe infection but the best measure of this deficiency is undecided. We investigated the influence of MBL functional deficiency on the development of sepsis in 195 adult patients, 166 of whom had bloodstream infection and 35 had pneumonia. Results were compared with 236 blood donor controls. MBL function (C4b deposition) and levels were measured by enzyme-linked immunosorbent assay. Using receiver-operator characteristics of MBL function in healthy controls, we identified a level of <0.2 U microL(-1) as a highly discriminative marker of low MBL2 genotypes. Median MBL function was lower in sepsis patients (0.18 U microL(-1)) than in controls (0.48 U microL(-1), P<0.001). MBL functional deficiency was more common in sepsis patients than controls (P<0.001). MBL functional deficient patients had significantly higher sequential organ failure assessment (SOFA) scores and higher MBL function and levels were found in patients with SOFA scores predictive of good outcome. Deficiency of MBL function appears to be associated with bloodstream infection and the development of septic shock. High MBL levels may be protective against severe sepsis.

Genetic polymorphism of the binding domain of surfactant protein-A2 increases susceptibility to meningococcal disease

BACKGROUND

Meningococcal disease occurs after colonization of the nasopharynx with Neisseria meningitidis. Surfactant protein (SP)-A and SP-D are pattern-recognition molecules of the respiratory tract that activate inflammatory and phagocytic defences after binding to microbial sugars. Variation in the genes of the surfactant proteins affects the expression and function of these molecules.

METHODS

Allele frequencies of SP-A1, SP-A2, and SP-D were determined by polymerase chain reaction in 303 patients with microbiologically proven meningococcal disease, including 18 patients who died, and 222 healthy control subjects.

RESULTS

Homozygosity of allele 1A1 of SP-A2 increased the risk of meningococcal disease (odds ratio [OR], 7.4; 95% confidence interval [CI], 1.3-42.4); carriage of 1A5 reduced the risk (OR, 0.3; 95% CI, 0.1-0.97). An analysis of the multiple single-nucleotide polymorphisms in SP-A demonstrated that homozygosity for alleles encoding lysine (in 1A1) rather than glutamine (in 1A5) at amino acid 223 in the carbohydrate recognition domain was associated with an increased risk of meningococcal disease (OR, 6.7; 95% CI, 1.4-31.5). Carriage of alleles encoding lysine at residue 223 was found in 61% of patients who died, compared with 35% of those who survived (OR adjusted for age, 2.9; 95% CI, 1.1-7.7). Genetic variation of SP-A1 and SP-D was not associated with meningococcal disease.

CONCLUSIONS

Gene polymorphism resulting in the substitution of glutamine with lysine at residue 223 in the carbohydrate recognition domain of SP-A2 increases susceptibility to meningococcal disease, as well as the risk of death.

Genetic susceptibility to infectious diseases: big is beautiful, but will bigger be even better?

Genetic epidemiology, including twin studies, provides robust evidence that genetic variation in human populations contributes to susceptibility to infectious disease. One of the major limitations of studies that attempt to identify the genes and mechanisms that underlie this susceptibility has been lack of power caused by small sample size. With the development of novel technologies, burgeoning information on the human genome, the HapMap project, and human genetic diversity, we are at the beginning of a new era in the study of the genetics of complex diseases. This review looks afresh at the epidemiological evidence that supports a role for genetics in susceptibility to infectious disease, examines the somewhat limited achievements to date, and discusses current advances in methodology and technology that will potentially lead to translational data in the future.

Serum mannose-binding lectin deficiency is associated with cryptosporidiosis in young Haitian children

BACKGROUND

Mannose-binding lectin (MBL) is a component of the innate immune response and binds microbial surfaces through carbohydrate recognition domains. MBL deficiency may contribute to susceptibility to a variety of infectious diseases, particularly in young children. MBL binds to the Cryptosporidium sporozoite and may be important in resistance to cryptosporidiosis.

METHODS

We studied the association of serum MBL levels and cryptosporidiosis in a case-control study of young Haitian children with cryptosporidiosis versus children who were control subjects.

RESULTS

Ninety-nine children were enrolled, as follows: 49 children with cryptosporidiosis, 41 healthy controls, and 9 children with diarrhea from other causes. Case children were more malnourished than controls, and 49% had persistent or chronic diarrhea. At enrollment, mean serum MBL levels were markedly lower in children with cryptosporidiosis (P = .002), as was the number of children with an MBL deficiency of < or = 70 ng/mL (P = .005). In multivariate analysis, the association of cryptosporidiosis and MBL deficiency persisted (P = .002; adjusted odds ratio, 22.4), as did the association of cryptosporidiosis with general malnutrition. The subset of children with cryptosporidiosis and MBL deficiency were more likely to be male (P = .025).

CONCLUSIONS

MBL may be an important component of innate immune protection against Cryptosporidium infection in young children. Additional studies are necessary to determine whether MBL intestinal losses, deficient epithelial expression, and/or genetic polymorphisms in the MBL gene contribute to MBL deficiency in cryptosporidiosis and other enteric infections in young children.

[Genetic polymorphisms and infections]

Recent studies have shown that genetic variants, responsible for the different human response when facing an infectious risk, concerned the genes of proteins involved in either recognition of the infectious agent, in the inflammatory cascade, or in the coagulation process. For example, some studies clearly demonstrated that if a twin was affected by an infectious disease, the risk of infection by the same agent for the other twin was significantly higher in homozygote than in heterozygote twins. In Caucasians, a punctual mutation of the TLR2 cytosol was proved to block the response to bacterial lipoproteins and to some Gram positive bacteria and could be responsible for a greater susceptibility to septic shock. Several polymorphisms of the tlr4 gene have been involved in the onset of septic shock in postsurgery infection due to Gram(-) bacilli. Paradoxically, these variants seemed to protect against legionellosis. In pediatrics, polymorphisms of tlr4 were also clearly identified as risk factors for meningococcemia of severe bronchiolitis due to the respiratory syncytial virus (RSV) in children under 2 years of age. A polymorphism of the TLR5 receptor gene, which creates a stop codon and which is responsible for a nonfunctionality of the receptor was associated with the onset of severe legionellosis. Analysing the functions of these genetic polymorphisms in the onset of sepsis will open the way to a lot of research on specific treatments focused on genetic abnormalities.

Invasive meningococcal disease associated with a very high case fatality rate in the North-West of Poland

The aim of the study was to investigate invasive meningococcal disease in the North-West of Poland, associated with a case fatality rate of 42.9%, where among the first 11 cases, eight had fatal outcome. All fatal cases were diagnosed as fulminant meningococcal severe sepsis with Waterhouse-Friderichsen syndrome and disseminated intravascular coagulation. Serotyping and pulsed-field gel electrophoresis analysis revealed that the high case fatality rate was not associated with the dissemination of one epidemic clone. However, six cases, all with good outcomes, were caused by C:2b:(P1.2,P1.5) isolates of the same pulsed-field gel electrophoresis type belonging to ST8 complex/Cluster A4.

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.

Polymorphisms in the mannose-binding lectin gene as determinants of age-defined risk of coronary artery lesions in Kawasaki disease

OBJECTIVE

To evaluate the relationship between polymorphisms in the gene coding for mannose-binding lectin (MBL) and the occurrence of coronary artery lesions (CALs) among different age groups of patients with Kawasaki disease.

METHODS

The frequencies of the genotypes, defined as mutations in codons 52, 54, and 57, and the functional promoter variants of the MBL2 gene were determined in 88 patients with acute Kawasaki disease (median age at onset 1.9 years). The possible influence of the MBL2 genotype on the development and progression of CALs in Kawasaki disease was assessed according to age categories and MBL genotypes in univariate and multivariate analyses.

RESULTS

In patients younger than age 1 year, we found an increased risk of developing CALs in the presence of a variant MBL2 genotype (P = 0.008). In contrast, in patients older than age 1 year, we found an increased risk of CALs in those patients with the wild-type genotype (P = 0.005).

CONCLUSION

Our findings indicate that MBL has an ambiguous role in Kawasaki disease and contributes differently to the pathophysiologic development of CALs, being protective in infants but potentially harmful in patients of older age. The data also imply that the standard treatment of intravenous immunoglobulins to reduce the development of lesions may not be as effective in the very young as it is in the older patients. For the very young, alternative or adjuvant treatment may be indicated, particularly in infants who are MBL-deficient.

Mannose-binding lectin gene polymorphism and its impact on human immunodeficiency virus 1 infection

Mannose-binding lectin (MBL) is a serum protein whose low concentration is associated with the occurrence of allele variants named MBL*B, MBL*C and MBL*D. The present study investigated the association between MBL gene polymorphism and the susceptibility to HIV-1 infection. The study of 145 HIV-1-infected subjects and 99 healthy controls showed the presence of alleles MBL*A, MBL*B and MBL*D, whose frequencies were 69%, 22% and 09% among patients and 71%, 13% and 16% among healthy controls, respectively. The presence of the variant MBL*B was associated with higher plasma viral load levels, suggesting the importance of the MBL gene polymorphism in the clinical evolution of HIV-1-infected patients.

Risk and protective factors for meningococcal disease in adolescents: matched cohort study

OBJECTIVE

To examine biological and social risk factors for meningococcal disease in adolescents.

DESIGN

Prospective, population based, matched cohort study with controls matched for age and sex in 1:1 matching. Controls were sought from the general practitioner.

SETTING

Six contiguous regions of England, which represent some 65% of the country's population.

PARTICIPANTS

15-19 year olds with meningococcal disease recruited at hospital admission in six regions (representing 65% of the population of England) from January 1999 to June 2000, and their matched controls.

METHODS

Blood samples and pernasal and throat swabs were taken from case patients at admission to hospital and from cases and matched controls at interview. Data on potential risk factors were gathered by confidential interview. Data were analysed by using univariate and multivariate conditional logistic regression.

RESULTS

144 case control pairs were recruited (74 male (51%); median age 17.6). 114 cases (79%) were confirmed microbiologically. Significant independent risk factors for meningococcal disease were history of preceding illness (matched odds ratio 2.9, 95% confidence interval 1.4 to 5.9), intimate kissing with multiple partners (3.7, 1.7 to 8.1), being a university student (3.4, 1.2 to 10) and preterm birth (3.7, 1.0 to 13.5). Religious observance (0.09, 0.02 to 0.6) and meningococcal vaccination (0.12, 0.04 to 0.4) were associated with protection.

CONCLUSIONS

Activities and events increasing risk for meningococcal disease in adolescence are different from in childhood. Students are at higher risk. Altering personal behaviours could moderate the risk. However, the development of further effective meningococcal vaccines remains a key public health priority.

MANNOSE-BINDING LECTIN POLYMORPHISMS IN SEVERE SEPSIS: RELATIONSHIP TO LEVELS, INCIDENCE, AND OUTCOME

Mannose-binding lectin (MBL) genetic polymorphisms result in deficiency of the encoded protein and increased susceptibility to infection, especially in children and the immunocompromised. The objective of this study was to investigate the relationship between MBL-2 exon 1 and promoter -221 polymorphisms, plasma levels of the encoded protein, and the incidence and outcome of severe sepsis and septic shock. One hundred seventy-four white adult patients with severe sepsis or septic shock were recruited in a prospective multicenter study across eight intensive care units in the South of England, UK. Genotype and haplotype frequencies were compared between normal population controls and patients, and between survivors and nonsurvivors. Plasma levels of encoded protein were related to genotype and outcome. The exon 1 polymorphisms (A/O or O/O) were significantly more common in the patients with severe sepsis and septic shock than in normal healthy adults (54.6% vs. 39.7%, P = 0.001), and there was a significant difference in haplotype frequency between controls and septic patients (P < 0.0001). There was no significant difference in MBL-2 genotype or haplotype frequency between survivors and nonsurvivors. There was a strong relationship between MBL-2 haplotype and plasma MBL concentration (P < 0.001). Individual plasma levels were variable and increased between days 1 and 7. The mortality rate was higher in those with MBL levels <1000 microg/L than in those patients with levels >1000 microg/L (47.2 vs. 22.2%, P = 0.05). We conclude that genetic polymorphisms resulting in mannose-binding lectin deficiency are associated with increased susceptibility to sepsis. The close relationship between polymorphic variants and plasma MBL concentration persists during sepsis but individual levels vary widely. Lower circulating MBL levels are associated with a poor outcome.

The mannose-binding lectin: a prototypic pattern recognition molecule

The innate immune system is comprised of a sophisticated network of recognition and effector molecules that act together to protect the host in the first minutes or hours of exposure to an infectious challenge. The mannose-binding lectin (MBL) is an evolutionary conserved circulating host defense protein that acts as a broad-spectrum recognition molecule against a wide variety of infectious agents. Target binding triggers the MBL pathway of complement activation. MBL can be considered conceptually as an 'ante-antibody' because it has a role in mammals during the lag period that is required to develop an antibody response against infectious agents. Additionally, there are MBL-like homologues in animals that lack adaptive immunity that activate a primitive complement system, and under these circumstances these MBL-like molecules play an analogous role to antibodies in higher animals. These molecules might be considered to be functional antecedents of antibodies. Recent work also indicates that MBL recognizes altered self-antigens, and as such MBL has a role that extends beyond a traditional role in first line host defense as it appears to play a role as a modulator of inflammation.

Critical determinants of the interactions of capsule-expressing Neisseria meningitidis with host cells: the role of receptor density in increased cellular targeting via the outer membrane Opa proteins

Neisseria meningitidis capsule is an important virulence determinant required for survival in the blood but is reportedly involved in inhibiting cellular interactions mediated by meningococcal outer membrane adhesins. However, evidence from our previous studies suggested that target receptor density on host cells may determine whether or not capsulate bacteria can adhere via outer membrane proteins such as Opa. To confirm this and evaluate the impact of capsulation on bacterial interactions, we used Opa(+) and Opa(-) derivatives of capsulate and acapsulate meningococcal isolates and transfected cell lines expressing CEACAM1, a receptor targeted by Opa proteins. To assess the extent and rate of cell association, subpopulations of stably transfected Chinese hamster ovary cells with different receptor levels were derived. A quantitative correlation of CEACAM1 levels and Opa-dependent binding of both capsulate and acapsulate bacteria was demonstrated, which was accelerated at high receptor densities. However, it appears that invasion by Opa(+) capsulate bacteria only occurs when a threshold level of CEACAM density has been reached. Target cells expressing high levels of CEACAM1 (MFI c. 400) bound threefold more, but internalized 20-fold more Opa(+) capsulate bacteria than those with intermediate expression (MFI c. 100). No overall selection of acapsulate phenotype was observed in the internalized population. These observations confirm that capsule may not be an adequate barrier for cellular interactions and demonstrate the role of a host factor that may determine capsulate bacterial invasion potential. Upregulation of CEACAMs, which can occur in response to inflammatory cytokines, could lead to translocation of a small number of fully capsulate bacteria across mucosal epithelium into the bloodstream sufficient to cause a rapid onset of disseminated disease. Thus the data also suggest a novel rationale for the epidemiological observations that individuals with prior infectious/inflammatory conditions carry a high risk of invasive meningococcal disease.

Mannose-binding lectin: biology and clinical implications

The innate host defence molecule mannose-binding lectin (MBL) has attracted great interest as a potential candidate for passive immunotherapy to prevent infection. MBL is a multimeric lectin that recognizes a wide array of pathogens independently of specific antibody, and initiates the lectin pathway of complement activation. The basic structural unit is a triple helix of MBL peptides, which aggregate into complement-fixing higher-order structures (tetramers, pentamers and hexamers). The gene encoding MBL, MBL2, contains several common polymorphisms that influence transcription and assembly of the molecule into multimers. MBL2 coding alleles associated with low blood levels are present in up to 40% of Caucasoids, with up to 8% having genotypes associated with profound reduction in circulating MBL levels. Low-producing MBL2 variants and low MBL levels are associated with increased susceptibility to and severity of a variety of infective illnesses, particularly when immunity is already compromised--for example, in infants and young children, patients with cystic fibrosis, and after chemotherapy and transplantation. These observations suggest that administration of recombinant or purified MBL may be of benefit in clinical settings where MBL deficiency is associated with a high burden of infection. This review provides a background to MBL biology and disease associations, and identifies the exciting therapeutic possibilities of MBL replacement.

Mannose-binding lectin in chronic hepatitis B virus infection

Mannose binding lectin (MBL) is a pattern-recognition molecule of the innate immune system. The roles of MBL and its gene (mbl2) polymorphisms, -221X/Y and codon 54A/B, in hepatitis B virus (HBV) infection were investigated in this study. We recruited 320 nonprogressed hepatitis B surface antigen (HBsAg) carriers; 199 progressed HBsAg carriers with hepatocellular carcinoma or cirrhosis; 87 spontaneously recovered individuals who were HBsAg negative and anti-HBs and anti HBc positive; and 484 controls who were naïve to HBV. There was no significant difference between nonprogressed carriers, spontaneously recovered individuals, and controls in terms of serum MBL levels and mbl2 polymorphisms distributions. However, the low MBL genotypes had a dose-dependent correlation with the cirrhosis and hepatocellular carcinoma in progressed carriers with odds ratios of 1.36 and 3.21 for the low and extremely low MBL genotypes, respectively (P = .01). The low-expression promoter haplotype XA (OR = 1.97) and the mutant haplotype YB (OR = 1.90) were also associated with the cirrhosis and hepatocellular carcinoma (P = .002). As expected, the lower serum MBL levels in progressed carriers as compared with nonprogressed carriers were due to an overrepresentation of low and extremely low MBL genotypes. Moreover, MBL could bind HBsAg in a dose- and calcium-dependent and mannan-inhibitable manner in vitro, suggesting that binding occurs via the carbohydrate recognition domains. This binding also enhanced C4 deposition. In conclusion, these results suggest that low MBL genotypes associate with the occurrence of cirrhosis and hepatocellular carcinoma in progressed HBsAg carriers, and MBL can bind HBsAg.

Function and heterogeneity of fish lectins

Lectins are primordial molecules with multiple known functions. They have been known to exist in fish and other animals for decades and were initially identified as (hem)agglutinins. Demonstration of the importance of vertebrate lectins in innate immunity is a recent effort and is still largely unrealised for fish. This mini-review will tabulate those fish lectins identified since the last major review. In addition, particular lectins for which either functional relevance or functional or structural heterogeneity has been demonstrated are discussed in greater detail.

Association of furunculosis and familial deficiency of mannose-binding lectin

BACKGROUND

Polymorphisms in the mannose-binding lectin gene reduce serum mannose-binding lectin levels and are associated with enhanced risk of infection. In a family with recurrent staphylococcal disease presenting as furunculosis or carbuncles, an association with mannose-binding lectin deficiency was investigated.

MATERIALS AND METHODS

Levels of functional mannose-binding lectin were estimated and the genotypes of the mannose-binding lectin gene were analysed on blood samples, collected from the members of one particular family with a high prevalence of furunculosis.

RESULTS

Functional mannose-binding lectin levels in sera of 13 of the 28 members of one family showed deficiency. Furunculosis or carbuncles appeared to be present in nine of the 28 family members, seven of which showing the pBly allele and mannose-binding lectin deficiency. Four young family members of the second generation were pBly positive and mannose-binding lectin deficient, but had not shown furunculosis yet.

CONCLUSION

Members of a particular family suffering from furunculosis differ from their 'healthy' relatives as to mannose-binding lectin genotypes, indicating the relevance of normal mannose-binding lectin levels in the defence against staphylococcal disease.

Binding of the complement inhibitor C4bp to serogroup B Neisseria meningitidis

Neisseria meningitidis (meningococcus) is an important cause of meningitis and sepsis. Currently, there is no effective vaccine against serogroup B meningococcal infection. Host defense against neisseriae requires the complement system (C) as indicated by the fact that individuals deficient in properdin or late C components (C6-9) have an increased susceptibility to recurrent neisserial infections. Because the classical pathway (CP) is required to initiate efficient complement activation on neisseriae, meningococci should be able to evade it to cause disease. To test this hypothesis, we studied the interactions of meningococci with the major CP inhibitor C4b-binding protein (C4bp). We tested C4bp binding to wild-type group B meningococcus strain (H44/76) and to 11 isogenic mutants thereof that differed in capsule expression, lipo-oligosaccharide sialylation, and/or expression of either porin (Por) A or PorB3. All strains expressing PorA bound radiolabeled C4bp, whereas the strains lacking PorA bound significantly less C4bp. Increased binding was observed under hypotonic conditions. Deleting PorB3 did not influence C4bp binding, but the presence of polysialic acid capsule reduced C4bp binding by 50%. Bound C4bp remained functionally active in that it promoted the inactivation of C4b by factor I. PorA-expressing strains were also more resistant to C lysis than PorA-negative strains in a serum bactericidal assay. Binding of C4bp thus helps Neisseria meningitidis to escape CP complement activation.

Mannose Binding Lectin Acute Phase Activity in Patients with Severe Infection

Mannose Binding Lectin (MBL) is a liver derived, circulating plasma protein that plays a pivotal role in innate immunity. MBL functions as a pathogen recognition molecule, opsonising organisms and initiating the complement cascade. MBL deficiency arising from mutations and promoter polymorphisms in the MBL2 gene is common and has been associated with risk, severity, and frequency of infection in a number of clinical settings. With MBL therapy on the horizon, the usefulness of replacement MBL therapy has been challenged by the notion, that as an acute phase protein, MBL levels may rise under stress to sufficient levels, in individuals who are usually deficient. This report demonstrates that in patients with sepsis and septic shock, the majority of patients do not display an MBL acute phase response: 41.4% of individuals maintained consistent MBL levels throughout hospital stay, 31.3% of individuals demonstrated a positive acute phase response, and a negative acute phase response was observed in 27.3% of individuals studied. Importantly, a positive acute phase response was generally observed in individuals with wild-type MBL2 genes. When a positive acute phase response was observed in individuals with coding mutation, these individuals demonstrated a normal MBL level on admission to hospital. Furthermore, no individual, regardless of genotype who was MBL deficient at admission was able to demonstrate a positive acute phase response into the normal MBL range. These findings indicate MBL demonstrates a variable acute phase response in the clinical setting of sepsis and septic shock.

Concept of PIRO as a new conceptual framework to understand sepsis

OBJECTIVE

To define and introduce the PIRO model for categorizing sepsis in infants and children.

DESIGN

A summary of the literature published during the 5 yrs since this concept has been formulated, along with a consensus opinion of experts in the field of sepsis and septic shock.

RESULTS

The imprecision and intrinsic heterogeneity of the patient population defined as septic has prompted the introduction of a new sepsis classification system known as PIRO. PIRO stands for predisposition, infection, response, and organ dysfunction. It is hoped that by defining the septic process through a detailed analysis of each of its component parts, the development of sepsis will be better understood. This may contribute to improved therapeutic interventions for sepsis in the future.

CONCLUSIONS

The PIRO model is a conceptual framework for understanding sepsis that has many favorable attributes. The PIRO model should be directly tested in both the research laboratory and in clinical trial designs to determine the practical value and clinical relevance of this new classification scheme for sepsis.

Genetic polymorphisms in sepsis

CONTEXT

Wide variability exists in the susceptibility to and outcome from sepsis even within similar intensive care unit populations. Some of this variability in the host may be due to genetic variation in genes coding for components of the innate immune response.

OBJECTIVE

To review the evidence for a genetic influence on the susceptibility to and outcome from sepsis.

DESIGN

Literature review.

PATIENTS

Variety of adult and pediatric patients with various critical illnesses and infections.

INTERVENTIONS

None.

MAIN OUTCOME MEASURES

Susceptibility to clinical symptoms of sepsis and outcome as measured by severity of disease and mortality.

RESULTS

Polymorphisms in genes coding for proteins involved in the recognition of bacterial pathogens (Toll-like receptor 4, CD14, Fc(gamma)RIIa, and mannose-binding lectin) and the response to bacterial pathogens (tumor necrosis factor-alpha, interleukin (IL)-1alpha, IL-1beta, IL-1 receptor agonist, IL-6, IL-10, heat shock proteins, angiotensin I converting enzyme, plasminogen activator inhibitor-1) can influence the amount or function of the protein produced in response to bacterial stimuli. Evidence is discussed suggesting that some of these genetic polymorphisms influence the susceptibility to and outcome from sepsis.

CONCLUSION

Host genetic variability in the regulatory and coding regions of genes for components of the innate immune system may influence the susceptibility to and/or outcome from sepsis. The disparate results observed in many studies of polymorphisms in sepsis emphasize the need for future studies to be larger, to include the analysis of multiple polymorphisms, and to be better designed with respect to control populations to identify the degree of influence that genetic variability has on sepsis.

Congenital immunodeficiencies and sepsis

OBJECTIVE

Because a hallmark of congenital immunodeficiency disorders is susceptibility to recurrent, unusual and/or severe infections, an effort was undertaken to identify a subset of these patients with an increased risk for sepsis.

DESIGN

Literature review.

RESULTS

Twenty congenital immunodeficiency disorders were identified with increased sepsis susceptibility.

CONCLUSION

Distinguishing patients with congenital immunodeficiencies from others with sepsis has important implications for the future well-being of the immunodeficient patient because many of the diseases are modified favorably by appropriate treatment. In addition, better understanding of sepsis in the setting of congenital immunodeficiency has numerous implications for both immunodeficiency and sepsis research. As a group, these disorders define components of the human immune system that are essential for defense against severe infection and demonstrate immunologic themes underlying sepsis susceptibility.

Mannose-binding lectin in severe acute respiratory syndrome coronavirus infection

Little is known about the innate immune response to severe acute respiratory syndrome (SARS) coronavirus (CoV) infection. Mannose-binding lectin (MBL), a key molecule in innate immunity, functions as an ante-antibody before the specific antibody response. Here, we describe a case-control study that included 569 patients with SARS and 1188 control subjects and used in vitro assays to investigate the role that MBL plays in SARS-CoV infection. The distribution of MBL gene polymorphisms was significantly different between patients with SARS and control subjects, with a higher frequency of haplotypes associated with low or deficient serum levels of MBL in patients with SARS than in control subjects. Serum levels of MBL were also significantly lower in patients with SARS than in control subjects. There was, however, no association between MBL genotypes, which are associated with low or deficient serum levels of MBL, and mortality related to SARS. MBL could bind SARS-CoV in a dose- and calcium-dependent and mannan-inhibitable fashion in vitro, suggesting that binding is through the carbohydrate recognition domains of MBL. Furthermore, deposition of complement C4 on SARS-CoV was enhanced by MBL. Inhibition of the infectivity of SARS-CoV by MBL in fetal rhesus kidney cells (FRhK-4) was also observed. These results suggest that MBL contributes to the first-line host defense against SARS-CoV and that MBL deficiency is a susceptibility factor for acquisition of SARS

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.