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

Advances in our understanding of the pathogenesis of hemolytic uremic syndromes

Hemolytic uremic syndrome (HUS) is major global health care issue as it is the leading cause of acute kidney injury in children. It is a triad of acute kidney injury, microangiopathic hemolytic anemia, and thrombocytopenia. In recent years, major advances in our understanding of complement-driven inherited rare forms of HUS have been achieved. However, in children 90% of cases of HUS are associated with a Shiga toxin-producing enteric pathogen. The precise pathological mechanisms in this setting are yet to be elucidated. The purpose of this review is to discuss advances in our understanding of the pathophysiology underlying HUS and identify the key questions yet to be answered by the scientific community.

Haemolytic uraemic syndrome

Haemolytic uraemic syndrome (HUS) is defined by the simultaneous occurrence of nonimmune haemolytic anaemia, thrombocytopenia and acute renal failure. This leads to the pathological lesion termed thrombotic microangiopathy, which mainly affects the kidney, as well as other organs. HUS is associated with endothelial cell injury and platelet activation, although the underlying cause may differ. Most cases of HUS are associated with gastrointestinal infection with Shiga toxin-producing enterohaemorrhagic Escherichia coli (EHEC) strains. Atypical HUS (aHUS) is associated with complement dysregulation due to mutations or autoantibodies. In this review, we will describe the causes of HUS. In addition, we will review the clinical, pathological, haematological and biochemical features, epidemiology and pathogenetic mechanisms as well as the biochemical, microbiological, immunological and genetic investigations leading to diagnosis. Understanding the underlying mechanisms of the different subtypes of HUS enables tailoring of appropriate treatment and management. To date, there is no specific treatment for EHEC-associated HUS but patients benefit from supportive care, whereas patients with aHUS are effectively treated with anti-C5 antibody to prevent recurrences, both before and after renal transplantation.

Human mannose-binding lectin inhibitor prevents Shiga toxin-induced renal injury

Hemolytic uremic syndrome caused by Shiga toxin-producing Escherichia coli (STEC HUS) is a worldwide endemic problem, and its pathophysiology is not fully elucidated. Here we tested whether the mannose-binding lectin (MBL2), an initiating factor of lectin complement pathway activation, plays a crucial role in STEC HUS. Using novel human MBL2-expressing mice (MBL2 KI) that lack murine Mbls (MBL2(+/+)Mbl1(-/-)Mbl2(-/-)), a novel STEC HUS model consisted of an intraperitoneal injection with Shiga toxin-2 (Stx-2) with or without anti-MBL2 antibody (3F8, intraperitoneal). Stx-2 induced weight loss, anemia, and thrombocytopenia and increased serum creatinine, free serum hemoglobin, and cystatin C levels, but a significantly decreased glomerular filtration rate compared with control/sham mice. Immunohistochemical staining revealed renal C3d deposition and fibrin deposition in glomeruli in Stx-2-injected mice. Treatment with 3F8 completely inhibited serum MBL2 levels and significantly attenuated Stx-2 induced-renal injury, free serum hemoglobin levels, renal C3d, and fibrin deposition and preserved the glomerular filtration rate. Thus, MBL2 inhibition significantly protected against complement activation and renal injury induced by Stx-2. This novel mouse model can be used to study the role of complement, particularly lectin pathway-mediated complement activation, in Stx-2-induced renal injury.

Enterohemorrhagic Escherichia coli Pathogenesis and the Host Response

Enterohemorrhagic Escherichia coli (EHEC) is a highly pathogenic bacterial strain capable of causing watery or bloody diarrhea, the latter termed hemorrhagic colitis, and hemolytic-uremic syndrome (HUS). HUS is defined as the simultaneous development of non-immune hemolytic anemia, thrombocytopenia, and acute renal failure. The mechanism by which EHEC bacteria colonize and cause severe colitis, followed by renal failure with activated blood cells, as well as neurological symptoms, involves the interaction of bacterial virulence factors and specific pathogen-associated molecular patterns with host cells as well as the host response. The innate immune host response comprises the release of antimicrobial peptides as well as cytokines and chemokines in addition to activation and/or injury to leukocytes, platelets, and erythrocytes and activation of the complement system. Some of the bacterial interactions with the host may be protective in nature, but, when excessive, contribute to extensive tissue injury, inflammation, and thrombosis, effects that may worsen the clinical outcome of EHEC infection. This article describes aspects of the host response occurring during EHEC infection and their effects on specific organs.

Advances in pathogenesis and therapy of hemolytic uremic syndrome caused by Shiga toxin-2

Shiga toxin (Stx) producing Escherichia coli (STEC) is responsible to bloody diarrhea (hemorrhagic colitis) and the hemolytic uremic syndrome (HUS). STEC strains carry inducible lambda phages integrated into their genomes that encode Stx 1 and/or 2, with several allelic variants each one. O157:H7 is the serotype that was documented in the vast majority of HUS cases although non-O157 serotypes have been increasingly reported to account for HUS cases. However, the outbreak that occurred in central Europe during late spring of 2011 showed that the pathogen was E. coli O104:H4. More than 4,000 persons were infected mainly in Germany, and it produced more than 900 cases of HUS resulting in 54 deaths. E. coli O104:H4 is a hybrid organism that combines some of the virulence genes of STEC and enteroaggregative E. coli specially production of Stx2 and the adherence mechanisms to intestinal epithelium. The differences in the epidemiology and presentation of E. coli pathogen meant a challenge for public health and scientific research to increase the knowledge of HUS-pathophysiology and to improve available therapies to treat HUS.

MBL Deficiency as Risk of Infection and Autoimmunity

In pathogen recognition by C-type lectins, several levels of complexity can be distinguished; these might modulate the immune response in different ways. Firstly, the pathogen-associated molecular pattern repertoire expressed at the microbial surface determines the interactions with specific receptors (Fig. 42.1). Secondly, each immune cell type possesses a specific set of pathogen-recognition receptors. Thirdly, changes in the cell-surface distribution of C-type lectins regulate carbohydrate binding by modulating receptor affinity for different ligands. Crosstalk between these receptors results in a network of multimolecular complexes, adding a further level of complexity in pathogen recognition (Cambi and Figdor 2005; Thiel et al. 2006) (see 10.1007/978-3-7091-1065-2_23). MBL deficiency is genetically determined and predisposes to recurrent infections and chronic inflammatory diseases. MBL deficiency has been implicated in susceptibility and course of viral, bacterial, fungal, and protozoan infection. More than 10% of the general population may, depending on definition, be classified as MBL deficient, underlining the redundancy of the immune system. MBL-disease association studies have been a fruitful area of research, which implicates a role for MBL in infective, inflammatory and autoimmune disease processes. MBL deficiency predisposes both to infection by extra-cellular pathogens and to autoimmune disease.

Genetic Polymorphisms of Molecules Associated with Innate Immune Responses, TRL2 and MBL2 Genes in Japanese Subjects with Functional Dyspepsia

Inflammatory changes in the gastric mucosa are commonly observed in Japanese patients with functional dyspepsia (FD). However, detailed data regarding the possible association between the genetic factors of inflammation related molecules and FD are not available. Toll like receptor 2 (TLR2) and mannan-binding lectin (MBL) protein play important roles in the innate immune activation. We aimed to clarify the association between common polymorphisms of TLR2 and MBL2 genes with FD in Japanese subjects. TLR2 −196 to −174 del and MBL2 codon54 G/A polymorphisms were genotyped in 111 FD patients according to Rome III criteria and 106 asymptomatic controls. Non-significant correlation was found between TLR2 and MBL2 polymorphisms with FD. However, in Helicobacter pylori (H. pylori) positives, we found significant inverse association between TLR2 −196 to −174 del carrier and FD among H. pylori positive subjects (Adjusted odds ratio (OR) = 0.48, 95% confidence interval (CI) = 0.23–0.996, p = 0.0488). We also found significant inverse association between the same genotype with postprandial distress syndrome (PDS) among H. pylori positive subjects (Adjusted OR = 0.22, 95% CI = 0.07–0.69, p = 0.0099). Our data suggest that TLR2 −196 to −174 del carriers’s status but not MBL2 codon54 G/A is inversely related to the risk with FD in H. pylori-infected subjects.

Mannan-binding lectin B allele is associated with a risk of developing more severe gastric mucosal atrophy in Helicobacter pylori-infected Japanese patients

OBJECTIVE

Mannan-binding lectin (MBL) is an important constituent of the innate immune system, and deficiency of MBL has been reported to increase the overall susceptibility of an individual to infectious disease. Codon 54 G/A variant of exon 1 (B allele) affects MBL2 gene and alters its activity. We investigated the influence of MBL2 variant on the risk of gastroduodenal diseases and on the severity of Helicobacter pylori-induced gastritis in a Japanese population.

METHODS

One hundred and two gastric ulcers, 48 duodenal ulcers, 275 nonulcer participants were included in this study. B allele of the MBL2 gene was detected by polymerase chain reaction based restriction fragment length polymorphism. The severity of the histological chronic gastritis in antral biopsy specimens were classified according to the updated Sydney system.

RESULTS

MBL2 B allele was significantly associated with severity of gastric mucosal atrophy and intestinal metaplasia (atrophy, G/G vs. G/A vs. A/A; P=0.02, A/A vs. others; P=0.009, intestinal metaplasia; G/G vs. G/A vs. A/A; P=0.03, A/A vs. others; P=0.004). When participants were divided into the following three groups according to the severity of gastric atrophy: the nonatrophic gastritis (NA) group, the severe atrophic gastritis (SA) group, and mild atrophic gastritis (MA) group, the frequency of A/A was significantly higher in the SA group than in others (SA vs. MA; odds ratio=8.42, 95% confidence interval=1.05-67.45, SA vs. others; odds ratio=10.06, 95% confidence interval=1.26-80.45).

CONCLUSION

Our data suggest that the MBL2 codon 54 B allele is associated with a risk of developing more severe gastric mucosal atrophy in H. pylori-infected Japanese patients.

Mannan-binding lectin (MBL) polymorphism and gastric cancer risk in Japanese population

BACKGROUND

Mannan-binding lectin (MBL) is believed to be an important constituent of the innate immune system. It has been reported that the codon 54 G/A polymorphism of exon-1 affects the MBL2 gene and alters its activity.

AIMS

We investigated the association between polymorphism of the MBL2 gene and gastric cancer risk as well as Helicobacter pylori infection in a Japanese population.

METHODS

The study cohort comprised 388 gastric cancer patients and 144 healthy volunteers. Polymorphism at codon 54 of exon 1 of the MBL2 gene was investigated by PCR-based restriction fragment length polymorphism analysis.

RESULTS

There was no significant difference in the distribution of the MBL2 genotype among the gastric cancer patients and healthy controls. However, the carrier of the A allele was more prevalent among patients with a more advanced stage gastric cancer [odds ratio (OR) 1.68, 95% confidence interval (CI) 1.05-2.67; P = 0.03] and also had an increased risk of gastric cancer among patients 65 years of age or younger (OR = 1.6, 95%CI = 1.01-2.52, <0.05).

CONCLUSION

The codon 54 polymorphism of the MBL2 gene is associated with more advanced phenotypes of gastric cancer and the risk of gastric cancer in Japanese patients 65 years of age or younger.

Mannose-binding lectin (MBL) facilitates opsonophagocytosis of yeasts but not of bacteria despite MBL binding

Mannose-binding lectin (MBL) is a serum protein of the innate immune system. After binding to a microorganism, MBL in complex with MBL-associated serine proteases activates the complement system, resulting in cleavage of complement factor C3. Cleaved C3 on the surface of the microorganism mediates opsonization for clearance, but the impact of MBL on subsequent phagocytosis has not been widely studied. We investigated the role of MBL in complement activation and phagocytosis of various bacteria and yeast species by flow cytometry. We measured both the C3 deposition during serum opsonization of fluorescent-labeled microorganisms as well as subsequent uptake of these microorganisms by human neutrophils. In MBL-deficient sera, a consistently decreased C3 deposition on both zymosan and Candida albicans was found and a reduced phagocytosis by neutrophils that was restored by exogenous MBL. This indicates that the lectin pathway of complement activation is important for the opsonophagocytosis of yeasts. In contrast, the C1q-dependent classical pathway dominated in the opsonization and phagocytosis of Staphylococcus aureus, Streptococcus pneumoniae, and Escherichia coli, whereas no effect of MBL was found. Both the lectin and the classical pathway of complement activation were highly amplified by the alternative route for opsonophagocytosis by neutrophils of yeast as well as microbial species. In summary, our data demonstrate that yeast species are preferentially opsonized and subsequently phagocytosed via activation of the lectin pathway of complement, whereas the uptake of bacterial strains was found to be largely MBL independent.

The Role of Mannan-Binding Lectin (MBL) Gene Polymorphism in Ulcerative Colitis

Series studies suggest that enteropathogenic microorganisms play a substantial role in the clinical initiation and relapses of ulcerative colitis (UC). Mannan-binding lectin (MBL) is an important constituent of the innate immune system, and deficiency of MBL has been reported to increase the overall susceptibility of an individual to infectious disease. This study was aimed to investigate the associations between polymorphisms of the MBL gene and UC. Recruited in this study were 108 Japanese patients with UC and 144 healthy control subjects. Polymorphism at codon 54 of exon 1 of the MBL gene was investigated by polymerase chain reaction based restriction fragment length polymorphism. In general, no significant difference in MBL polymorphism was found between UC patients and health controls. However, the frequency of A carriers was significantly higher in the relapsing cases than controls (Odds ration = 2.19, 95%CI, 1.10-4.34; p = 0.023), and similar tendency was also found in A/A genotype. In conclusion, the polymorphism at codon 54 of exon 1 of the MBL gene associated with the susceptibility to the relapsing phenotype of ulcerative colitis. It suggests that codon 54 A variants of MBL gene may have an increased risk for the flare-ups of UC.

Mannose-binding lectin and maladies of the bowel and liver

Mannose-binding lectin (MBL) is a pattern-recognition molecule that binds to characteristic carbohydrate motifs present on the surface of many different pathogens. MBL binding stimulates the immune system via the lectin pathway of complement activation. In certain clinical situations, often characterized by pre-existing immune compromise, MBL deficiency increases the risk of infectious and other disease-specific complications. Many of the key pathogenic processes inherent to common gastroenterological diseases, such as infection, immunological damage, and carcinogenesis, have been linked to MBL. This editorial reviews the biology of MBL, outlines key disease associations to document the breadth of influence of MBL, and finally, highlights the relevance of MBL to both gastroenterological health and disease.