Mannose-binding lectin deficiency and predisposition to recurrent infection in adults

Levels of mannose-binding lectin (MBL) associates with sepsis-related in-hospital mortality in women

Background

Mannose-binding lectin (MBL) mediates the innate immune response either through direct opsonisation of microorganisms or through activation of the complement system. There are conflicting data whether MBL deficiency leads to increased susceptibility to infections or not. The aim of this study was to determine if low levels of mannose-binding lectin (MBL) predict sepsis development, sepsis severity and outcome from severe sepsis or septic shock.

Method

Patients aged 18 years or more with documented sepsis within 24 h after admission to the intensive care unit were included if they had participated in a health survey and donated blood samples prior to the sepsis event. A subset of these patients had stored plasma also from the acute phase. Two matched referents free of known sepsis were selected for each case. Plasma levels MBL were determined in stored samples from health surveys (baseline) and from ICU admission (acute phase). The association between MBL and sepsis, sepsis severity and in-hospital mortality were determined with 1300 ng/mL as cut-off for low levels.

Results

We identified 148 patients (61.5% women) with a first-time sepsis event 6.5 years (median with IQR 7.7) after participation in a health survey, of which 122 also had samples from the acute septic phase. Both high MBL levels in the acute phase (odds ratio [95% confidence interval]) (2.84 [1.20-6.26]), and an increase in MBL levels from baseline to the acute phase (3.76 [1.21-11.72]) were associated with increased risk for in-hospital death in women, but not in men (0.47 [0.11-2.06]). Baseline MBL levels did not predict future sepsis, sepsis severity or in-hospital mortality.

Conclusions

An increase from baseline to the acute phase as well as high levels in the acute phase associated with an unfavourable outcome in women.

Genetics in community-acquired pneumonia

PURPOSE OF REVIEW

Host defense against community-acquired pneumonia depends on an intact innate and acquired immune system. This review analyses the correlation between specific defects and polymorphisms of immunity genes with susceptibility for pneumonia.

RECENT FINDINGS

Mutations in BTK, Bruton's tyrosine kinase, lead to X-linked agammaglobulinemia, a disease characterized by recurrent respiratory tract infections, including pneumonia. BTK inhibitors, which are used for treatment of leukemia, have pneumonia as side effect. Polymorphisms in B lymphocyte growth and differentiation factors, including IL-6 and IL-10, Fcg RIIa receptors, as well as genetic variants of ACE, angiotensin-converting enzyme, also are associated with increased susceptibility for pneumonia.

SUMMARY

Delineation of underlying genetic defects and polymorphisms may add in diagnosis, therapy, and prognosis of community-acquired pneumonia. In case of humoral immunodeficiency, antibody replacement therapy may be indicated.

Mannose Binding Lectin, S100 B Protein, and Brain Injuries in Neonates With Perinatal Asphyxia

Perinatal asphyxia triggers an acute inflammatory response in the injured brain. Complement activation and neuroinflammation worsen brain damage after a systemic ischemia/reperfusion insult. The increase of mannose binding lectin (MBL) during asphyxia may contribute to the brain damage, via activation of the complement lectin pathway. The possible role of MBL2 gene variants in influencing the severity of post-asphyxia brain injuries is still unexplored. This retrospective study included 53 asphyxiated neonates: 42 underwent therapeutic hypothermia (TH) and 11 did not because they were admitted to the NICU later than 6 h after the hypoxic insult. Blood samples from TH-treated and untreated patients were genotyped for MBL2 gene variants, and biomarker plasma levels (MBL and S100 B protein) were measured at different time points: during hypothermia, during rewarming, and at 7-10 days of life. The timing of blood sampling, except for the T1 sample, was the same in untreated infants. Highest (peak) levels of MBL and MBL2 genotypes were correlated to neuroimaging brain damage or death and long-term neurodevelopmental delay. MBL2 wild-type genotype was associated with the highest MBL levels and worst brain damage on MRI (p = 0.046) at 7-10 days after hypoxia. MBL increased in both groups and S100B decreased, slightly more in treated than in untreated neonates. The progressive increase of MBL (p = 0.08) and to be untreated with TH (p = 0.08) increased the risk of brain damage or death at 7-10 days of life, without affecting neurodevelopmental outcomes at 1 year. The effect of TH on MBL plasma profiles is uncertain.

Complement deficiencies and dysregulation: Pathophysiological consequences, modern analysis, and clinical management

Complement defects are associated with an enhanced risk of a broad spectrum of infectious as well as systemic or local inflammatory and thrombotic disorders. Inherited complement deficiencies have been described for virtually all complement components but can be mimicked by autoantibodies, interfering with the activity of specific complement components, convertases or regulators. While being rare, diseases related to complement deficiencies are often severe with a frequent but not exclusive manifestation during childhood. Whereas defects of early components of the classical pathway significantly increase the risk of autoimmune disorders, lack of components of the terminal pathway as well as of properdin are associated with an enhanced susceptibility to meningococcal infections. The impaired synthesis or function of C1 inhibitor results in the development of hereditary angioedema (HAE). Furthermore, complement dysregulation causes renal disorders such as atypical hemolytic uremic syndrome (aHUS) or C3 glomerulopathy (C3G) but also age-related macular degeneration (AMD). While paroxysmal nocturnal hemoglobinuria (PNH) results from the combined deficiency of the regulatory complement proteins CD55 and CD59, which is caused by somatic mutation of a common membrane anchor, isolated CD55 or CD59 deficiency is associated with the CHAPLE syndrome and polyneuropathy, respectively. Here, we provide an overview on clinical disorders related to complement deficiencies or dysregulation and describe diagnostic strategies required for their comprehensive molecular characterization - a prerequisite for informed decisions on the therapeutic management of these disorders.

Pattern Recognition Molecules of the Lectin Pathway-Screening of Patients with Suspected Immunodeficiency

PURPOSE

To compare plasma concentrations of all lectin pathway (LP) pattern recognition molecules (PRMs) in patients referred for laboratory evaluation due to recurrent infections with healthy individuals.

METHODS

Patients were divided into categories according to referral: recurrent airway infections (RAI), recurrent abscesses, common variable immunodeficiency (CVID), lung transplantation candidates (LTX), and 'other causes'. LP PRMs (mannose-binding lectin (MBL), collectin liver 1 (CL-L1), H-ficolin, L-ficolin, M-ficolin) and C-reactive protein (CRP) were determined in 332 patients and 150 healthy blood donors using time-resolved immunofluorometric assays.

RESULTS

None of the LP PRMs was found in lower concentration in the patient categories; however, several PRMs were detected in higher concentrations. M-ficolin was found in higher concentrations in all patient categories. Patients suffering from RAI had higher concentrations of CL-L1 and H-ficolin. Patients suffering from abscesses exhibited higher concentrations of MBL and CL-L1, whereas LTX had higher concentrations of MBL. Patients with other causes of referral had higher concentrations of MBL and CL-L1. Prevalence of combined deficiencies of PRMs in patient categories and controls did not differ. CRP was used as a marker of ongoing inflammation and was significantly higher among all patient categories. Furthermore, CRP was found to correlate with both M-ficolin and L-ficolin.

CONCLUSION

The results suggest that neither single nor combined deficiencies of LP PRMs are more frequent among patients referred for an immunological evaluation than in healthy individuals. Future studies are needed and should focus on deficiencies of LP PRMs combined with deficiencies in other parts of the immune system.

Risk factors of laryngeal cryptococcosis: A case report

Cryptococcal infections are acquired by inhalation of encapsulated yeast cells or basidiospores. While Cryptococcus has a propensity to invade the lungs and central nervous system, other sites can be affected. Laryngeal cryptococcosis is rare with less than 30 previously reported cases, which commonly occurred in apparently immunocompetent hosts on inhaled corticosteroids. We present a case of laryngeal cryptococcosis with a long-term inhaled corticosteroid use, co-infection of pulmonary Mycobacterium avium-intracellulare, and mannose-binding lectin deficiency.

Impact of MBL2 gene polymorphisms on the risk of infection in solid organ transplant recipients: A systematic review and meta-analysis

Mannose-binding lectin (MBL) is a soluble pattern recognition molecule involved in complement activation. Single nucleotide polymorphisms (SNPs) in the MBL2 gene have been associated with susceptibility to infection, although data in solid organ transplant recipients remains inconclusive. This meta-analysis was primarily aimed at investigating the association between posttransplant bacterial and fungal infection and variant alleles of MBL2 gene SNPs in the promoter/5' untranslated region and exon 1. Cytomegalovirus (CMV) infection and/or disease were considered secondary outcomes. PubMed, EMBASE, and Web of Knowledge were searched for relevant articles up to August 2018. Eleven studies (comprising 1858 patients) were included, with liver transplant (LT) recipients accounting for 80.4% of the pooled population. As compared to high-MBL expression haplotypes (YA/YA, YA/XA), any MBL-deficient haplotype was associated with an increased risk of posttransplant bacterial and fungal infections (risk ratio [RR]: 1.30; P = .04). Low/null-MBL expression haplotypes (XA/O, O/O) also increased the risk of primary outcome (RR: 1.51; P = .008) and CMV events (RR: 1.50; P = .006). No effect was observed for individual promoter SNPs. In conclusion, MBL-deficient haplotypes are associated with a significant, albeit moderate, increase in the risk of posttransplant infection, with this association being mainly restricted to LT recipients.

Mannose-Binding Lectin-Deficient Donors Increase the Risk of Bacterial Infection and Bacterial Infection-Related Mortality After Liver Transplantation

Mannose-binding lectin (MBL) is synthesized by the liver and binds to microbes. MBL2 gene polymorphisms produce intermediate/low/null or normal MBL serum levels (MBL-deficient or MBL-sufficient phenotypes, respectively). We aimed to evaluate the incidence and severity of infection, rejection, and survival within 1 year after liver transplantation (LT) according to donor and recipient MBL2 gene polymorphisms. A repeated-event analysis for infection episodes (negative binomial regression, Andersen-Gill model) was performed in 240 LTs. Four hundred twenty-eight infectious episodes (310 bacterial, 15 fungal, 65 cytomegalovirus [CMV]-related, and 38 viral non-CMV-related episodes) and 48 rejection episodes were recorded. The main bacterial infections were urinary (n = 82, 26%) and pneumonia (n = 69, 22%). LT recipients of MBL-deficient livers had a higher risk of bacterial infection (incidence rate ratio [IRR] 1.48 [95% confidence interval 1.04-2.09], p = 0.028), pneumonia (IRR 2.4 [95% confidence interval 1.33-4.33], p = 0.013), and septic shock (IRR 5.62 [95% confidence interval 1.92-16.4], p = 0.002) compared with recipients of MBL-deficient livers. The 1-year bacterial infection-related mortality was higher in recipients of MBL-deficient versus MBL-sufficient livers (65.8% vs. 56.1%, respectively; p = 0.0097). The incidence of rejection, viral, or fungal infection was similar in both groups. Recipient MBL2 genotype did not significantly increase the risk of bacterial infection. LT recipients of MBL-deficient livers have a higher risk of bacterial infection, pneumonia, septic shock, and 1-year bacterial infection-related mortality after LT.

Sterile Inflammation of Brain, due to Activation of Innate Immunity, as a Culprit in Psychiatric Disorders

Evidence has accumulated that the occurrence of psychiatric disorders is related to chronic inflammation. In support of this linkage, changes in the levels of circulating pro-inflammatory cytokines and chemokines in the peripheral blood (PB) of psychiatric patients as well as correlations between chronic inflammatory processes and psychiatric disorders have been described. Furthermore, an inflammatory process known as "sterile inflammation" when initiated directly in brain tissue may trigger the onset of psychoses. In this review, we will present the hypothesis that prolonged or chronic activation of the complement cascade (ComC) directly triggers inflammation in the brain and affects the proper function of this organ. Based on the current literature and our own work on mechanisms activating the ComC we hypothesize that inflammation in the brain is initiated by the mannan-binding lectin pathway of ComC activation. This activation is triggered by an increase in brain tissue of danger-associated molecular pattern (DAMP) mediators, including extracellular ATP and high-mobility group box 1 (HMGB1) protein, which are recognized by circulating pattern-recognition receptors, including mannan-binding lectin (MBL), that activate the ComC. On the other hand, this process is controlled by the anti-inflammatory action of heme oxygenase 1 (HO-1). In this review, we will try to connect changes in the release of DAMPs in the brain with inflammatory processes triggered by the innate immunity involving activation of the ComC as well as the inflammation-limiting effects of the anti-inflammatory HO-1 pathway. We will also discuss parallel observations that during ComC activation subsets of stem cells are mobilized into PB from bone marrow that are potentially involved in repair mechanisms.

Innate Immunity and Mobilization of Hematopoietic Stem Cells

PURPOSE OF REVIEW

Several mechanisms have been postulated to orchestrate mobilization of hematopoietic stem/progenitor cells (HSPCs), and still more work is needed to better understand this process and to gain better mechanistic insight.

RECENT FINDINGS

Evidence accumulated that mobilization of HSPCs is a part of innate immunity response to tissue organ injury, stress, and infection. This evolutionary ancient process is orchestrated by granulocytes and monocytes that trigger activation of complement cascade and the coagulation cascade.

SUMMARY

We will present data from our laboratory that initiation of complement cascade activation and subsequently activation of the coagulation cascade during mobilization process are dependent on mannan-binding lectin (MBL). The mannan-binding pathway activates MBL-associated serine proteases (MASP-1 and MASP-2) that cleave the third complement component C3 and prothrombin. Cleavage of C3 leads to formation of classical C5 convertase and cleavage of prothrombin generates thrombin, which has "C5-like convertase" activity. Finally, both C5 convertase and thrombin cleave the fifth complement component C5, and activate distal part of the complement cascade that is crucial for egress of HSCPs from bone marrow niches into peripheral blood.

Mannose-binding lectin deficiency in respiratory diseases

Mannosebinding lectin is a part of the innate immunity that, being the first barrier of the antiinfectious defense, acts in first minutes or hours after pathogen challenge. The review provides data about mechanisms of action of mannosebinding lectin and its particular pathogenic role in a wide range of respiratory diseases: bacterial pneumonia, viral respiratory tract infections, tuberculosis, cystic fibrosis, chronic obstructive pulmonary disease, and asthma in adults and children.