Deficiency of mannose-binding lectin and burden of infection in children with malignancy: a prospective study

Immunodeficiency and genetic conditions that cause arthritis in childhood

Many conditions can cause or be associated with arthritis in childhood. The authors of this paper will review the situations in which underlying immunodeficiency or defective regulation of lymphocyte homeostasis must be suspected, and discuss, for some of these diseases, the genetic bases and pathogenesis. In the second part of this article, the authors will focus on other diseases that can cause arthritis in childhood, often with other symptoms, and for which evidence of an association with genetic abnormalities has been recently discovered. Finally, the authors will discuss the implications of recent findings regarding the role of some genes as causing or modulating factors in juvenile idiopathic arthritis and related disorders, as well as observations made in adults and in animal models of inflammation and autoimmunity.

Mannan-binding lectin and its role in innate immunity

Mannan-binding lectin (MBL) is a plasma collectin (C-type lectin with a collagen-like domain) and is considered an important component of innate immunity. Circulating MBL is genetically determined for the major part, but plasma concentration is also markedly influenced by nongenetic factors. The carbohydrate-binding ability of MBL can be inhibited by simple sugars like mannose, fucose and N-acetylglucosamine, but its greatest avidity appears to be for repeating mannose-based structural patterns typical of microbial surfaces. By this means, MBL can bind to a wide variety of bacteria and other microbes, neutralizing them and/or opsonizing them by activating complement using the recently discovered lectin pathway of complement activation. Individual humans differ 1000-fold in MBL concentration, and individuals with low circulating MBL appear to be more vulnerable to infections in a number of clinical settings, especially when combined with secondary immune deficiency. The best evidence that MBL deficiency or insufficiency is physiologically relevant comes from a rapidly expanding literature of clinical studies. MBL insufficiency appears to be a significant risk factor for infections in infants, and for individuals of any age undergoing chemotherapy or post-transplant immunosuppression. Moreover, MBL appears to have a significant influence on the course of certain chronic diseases like rheumatoid arthritis and cystic fibrosis. Replacement therapy with a plasma-derived product is safe and seems promising, while recombinant MBL provides hope for large-scale therapeutic applications. Randomized clinical trials of MBL therapy, which are now on the horizon, should provide unambiguous evidence for the physiological significance of MBL in innate immunity.

Serum concentration of Hakata antigen, a member of the ficolins, is linked with inhibition of Aerococcus viridans growth

BACKGROUND

Hakata antigen (Hakata) is a novel serum glycoprotein that consists of collagen- and fibrinogen-like domains, similar to ficolin/p35. Our research suggested that serum Hakata may be a target of a polysaccharide (PSA) produced by Aerococcus viridans.

METHODS

A. viridans was incubated with human plasma and Hakata-depleted plasma to examine Hakata binding and growth inhibition of A. viridans through binding with PSA.

RESULTS

When A. viridans was mixed with human acid citrate dextrose-one (ACD-A) plasma, it pulled down Hakata complexed with mannose-binding lectin (MBL)-associated serine proteases 1 and 2 (MASP-1 and MASP-2). This complex had the potential for C4 deposition. Serum Hakata circulates as Hakata-MASPs complex in the blood and is proteolytically active. By mixing A. viridans with human plasma, we prepared a Hakata-depleted plasma, deficient in Hakata-MASPs complex. This plasma failed to inhibit A. viridans growth plasma, but does not inhibit Staphylococcus aureus, Yersinia enterocolitica and Escherichia coli. However, a decrease of growth inhibition of A. viridans in Hakata-depleted plasma could be restored by adding a Hakata-MASPs complex preparation in a dose-dependent manner. On the other hand, the Hakata-MASPs complex exhibited strong binding to A. viridans, but not to S. aureus, Y. enterocolitica and E. coli.

CONCLUSIONS

The serum concentration of Hakata is linked with growth inhibition of A. viridans upon binding of Hakata via PSA.

Treatment of febrile neutropenia: what is new?

PURPOSE OF THE REVIEW

To identify the more recent challenges in the treatment of patients with febrile neutropenia following antineoplastic chemotherapy or bone marrow transplant published in the English language in the period late 2000-early 2002 regarding: changes in etiology of bacteremia in neutropenic patients; new options for initial empirical antibacterial therapy; factors associated with the risk of developing infection in cancer patients; prediction of prognosis in febrile neutropenia; oral therapy; need for a specific anti-Gram-positive coverage in persistently febrile and neutropenic patients.

RECENT FINDINGS

Findings may be summarized according with the identified topics as follows: many centers are reporting an increase in the incidence of Gram-negative bacteremias; piperacillin-tazobactam could be safely administered as monotherapy of febrile neutropenia; congenital factors and intensity of chemotherapy and other medical interventions, such as antifungal prophylaxis, are recognized as of increasing importance in the determination of infectious risk; it is now possible to identify patients with a good prognosis (low risk) by means of validated scoring systems; oral therapy is feasible in low risk patients; the empirical addition of a glycopeptide in persistently febrile neutropenic patients is not indicated.

SUMMARY

Many of the identified points may have a great impact in the daily management of febrile granulocytopenic patients. However, all recent epidemiological and therapeutical studies underline the absoloute need for the knowledge of the pattern of infecting organisms in each center.

Mannose-binding lectin (MBL) mutants are susceptible to matrix metalloproteinase proteolysis: potential role in human MBL deficiency

Mannose-binding lectin (MBL) plays a critical role in innate immunity. Point mutations in the collagen-like domain (R32C, G34D, or G37E) of MBL cause a serum deficiency, predisposing patients to infections and diseases such as rheumatoid arthritis. We examined whether MBL mutants show enhanced susceptibility to proteolysis by matrix metalloproteinases (MMPs), which are important mediators in inflammatory tissue destruction. Human and rat MBL were resistant to proteolysis in the native state but were cleaved selectively within the collagen-like domain by multiple MMPs after heat denaturation. In contrast, rat MBL with mutations homologous to those of the human variants (R23C, G25D, or G28E) was cleaved efficiently without denaturation in the collagen-like domain by MMP-2 and MMP-9 (gelatinases A and B) and MMP-14 (membrane type-1 MMP), as well as by MMP-1 (collagenase-1), MMP-8 (neutrophil collagenase), MMP-3 (stromelysin-1), neutrophil elastase, and bacterial collagenase. Sites and order of cleavage of the rat MBL mutants for MMP-2 and MMP-9 were: Gly(45)-Lys(46) --> Gly(51)-Ser(52) --> Gly(63)-Gln(64) --> Asn(80)-Met(81) which differed from that of MMP-14, Gly(39)-Leu(40) --> Asn(80)-Met(81), revealing that the MMPs were not functionally interchangeable. These sites were homologous to those cleaved in denatured human MBL. Hence, perturbation of the collagen-like structure of MBL by natural mutations or by denaturation renders MBL susceptible to MMP cleavage. MMPs are likely to contribute to MBL deficiency in individuals with variant alleles and may also be involved in clearance of MBL and modulation of the host response in normal individuals.

Mannose-binding lectin gene polymorphisms are associated with major infection following allogeneic hemopoietic stem cell transplantation

Life-threatening complications such as graft versus host disease and infection remain major barriers to the success of allogeneic hemopoietic stem cell transplantation (SCT). While pretransplantation conditioning and posttransplantation immunosuppression are important risk factors for infection, the reasons that similarly immunosuppressed transplant recipients show marked variation in frequency of infection after allogeneic SCT are unclear. Mannose-binding lectin (MBL) deficiency is a risk factor for infection in other situations where immunity is compromised. We investigated associations between MBL2 gene polymorphisms and risk of major infection following allogeneic SCT. Ninety-seven related allogeneic donor-recipient pairs were studied. Clinical data including survival, days of fever, graft versus host disease incidence and severity, and infection were collected by case note review. Five single-nucleotide polymorphisms in the MBL2 gene were genotyped using the polymerase chain reaction and sequence-specific primers. MBL2 coding mutations were associated with an increased risk of major infection following transplantation. This association was seen for donor (P =.002, odds ratio [OR] 4.1) and recipient (P =.04, OR 2.6) MBL2 genotype. MBL2 promoter variants were also associated with major infection. The high-producing haplotype HYA was associated with a markedly reduced risk of infection (recipient HYA P =.0001, OR 0.16; donor HYA P =.001, OR 0.23). Donor MBL2 coding mutations and recipient HYA haplotype were independently associated with infection in multivariate analysis. These results suggest that MBL2 genotype influences the risk of infection following allogeneic SCT and that both donor and recipient MBL2 genotype are important. These findings raise the possibility that MBL replacement therapy may be useful following transplantation.

Dominant effects of mutations in the collagenous domain of mannose-binding protein

Individuals heterozygous for mutant alleles encoding serum mannose-binding protein (MBP, also known as mannose-binding lectin) show increased susceptibility to infections caused by a wide range of pathogenic microorganisms. To investigate the molecular defects associated with heterozygosity, wild-type rat serum MBP polypeptides (MBP-A: 56% identical in sequence to human MBP) and rat MBP polypeptides containing mutations associated with human immunodeficiency have been coexpressed using a well-characterized mammalian expression system. The resulting proteins are secreted almost exclusively as heterooligomers that are defective in activating the complement cascade. Functional defects are caused by structural changes to the N-terminal collagenous and cysteine-rich domains of MBP, disrupting interactions with associated serine proteases. The dominant effects of the mutations demonstrate how the presence of a single mutant allele gives rise to the molecular defects that lead to the disease phenotype in heterozygous individuals.

The era of genomics: impact on sepsis clinical trial design

OBJECTIVE

This article aims to address the predictable impact of genetics on the design of clinical trials in the field of critical care medicine, with emphasis on the pathophysiology of sepsis and its treatment.

DATA SOURCES

Published articles reporting studies on sepsis and septic shock or assessing the influence of genetics and pharmacogenomics in the treatment of critical illnesses.

DATA ANALYSIS

Because most common diseases including sepsis have been shown to be influenced by inherited differences in our genes, completion of the Human Genome Project and the concomitant publication of the human single nucleotide polymorphism map both contribute to change our approach to medicine. Advances in genotyping techniques and bioinformatics enabling detection of single nucleotide polymorphisms have caused an explosion in pharmacogenomics-the research dealing with the interactions of an individual's genotype and the outcome of a drug therapy. Pharmacogenomics will undoubtedly be used to improve future health care and clinical research in different ways. Whereas treatment allocation has been based mainly on phenotype, genetic characterization will help researchers to identify suitable subjects for clinical trials, to facilitate interpretation of the results of clinical trials, and to identify novel targets for future drugs or new markets for current products. As interindividual variability in drug response is a substantial clinical problem, the second major objective of pharmacogenomic research is to decrease adverse responses to therapy through determination of adequate therapeutic targets and genetic polymorphisms that alter drug specificity and toxicity. Ultimately, genetic information will be used to select the most effective therapeutic agent and the optimal dosage to elicit the expected drug response for a given individual. Implementation of genetic criteria for stratification of patient populations and individual assessment of treatment risks and benefits emerges as a major challenge to the pharmaceutical industry.

CONCLUSIONS

In the future, technologies such as gene chip array will enhance genetic medicine and provide novel insights into a patient's susceptibility to disease, enabling a better assessment of prognostic risk factors, quicker diagnosis, and accurate prediction of individual responsiveness to drugs. The predictable consequences of such an approach on the prevention and treatment of diseases could revolutionize medicine.

Collections and ficolins: humoral lectins of the innate immune defense

Collectins and ficolins, present in plasma and on mucosal surfaces, are humoral molecules of the innate immune systems, which recognize pathogen-associated molecular patterns. The human collectins, mannan-binding lectin (MBL) and surfactant protein A and D (SP-A and SP-D), are oligomeric proteins composed of carbohydrate-recognition domains (CRDs) attached to collagenous regions and are thus structurally similar to the ficolins, L-ficolin, M-ficolin, and H-ficolin. However, they make use of different CRD structures: C-type lectin domains for the collectins and fibrinogen-like domains for the ficolins. Upon recognition of the infectious agent, MBL and the ficolins initiate the lectin pathway of complement activation through attached serine proteases (MASPs), whereas SP-A and SP-D rely on other effector mechanisms: direct opsonization, neutralization, and agglutination. This limits the infection and concurrently orchestrates the subsequent adaptive immune response. Deficiencies of the proteins may predispose to infections or other complications, e.g., reperfusion injuries or autoimmune diseases. Structure, function, clinical implications, and phylogeny are reviewed.

Genetics of susceptibility to human infectious disease

Before Robert Koch's work in the late nineteenth century, diseases such as tuberculosis and leprosy were widely believed to be inherited disorders. Heritability of susceptibility to several infectious diseases has been confirmed by studies in the twentieth century. Infectious diseases, old and new, continue to be an important cause of mortality worldwide. A greater understanding of disease processes is needed if more effective therapies and more useful vaccines are to be produced. As part of this effort, developments in genetics have allowed a more systematic study of the impact that the human genome and infectious disease have on each other.