Inherited complement deficiency in children surviving fulminant meningococcal septic shock

Complement factor D is linked to platelet activation in human and rodent sepsis

BACKGROUND

The complement factor D (CFD) exerts a regulatory role during infection. However, its physiological function in coagulopathy and its impact on the course of an infection remains unclear.

MATERIALS

Wild-type and CFD-deficient mice (n = 91) were subjected to cecal ligation and puncture to induce sepsis. At several time points, markers of coagulation and the host-immune response were determined. Furthermore, in patients (n = 79) with sepsis or SIRS, CFD levels were related to clinical characteristics, use of antiplatelet drugs and outcome.

RESULTS

Septic CFD-deficient mice displayed higher TAT complexes (p = 0.02), impaired maximal clot firmness, but no relevant platelet drop and reduced GPIIb/IIIa surface expression on platelets (p = 0.03) compared to septic wild-type mice. In humans, higher CFD levels (non-survivors, 5.0 µg/ml to survivors, 3.6 µg/ml; p = 0.015) were associated with organ failure (SOFA score: r = 0.33; p = 0.003) and mortality (75% percentile, 61.1% to 25% percentile, 26.3%). CFD level was lower in patients with antiplatelet drugs (4.5-5.3 µg/ml) than in patients without.

CONCLUSION

In mice, CFD is linked to pronounced platelet activation, depicted by higher GPIIb/IIIa surface expression in wild-type mice. This might be of clinical importance since high CFD plasma concentrations were also associated with increased mortality in sepsis patients.

Activated Complement Factors as Disease Markers for Sepsis

Sepsis is a leading cause of death in the United States and worldwide. Early recognition and effective management are essential for improved outcome. However, early recognition is impeded by lack of clinically utilized biomarkers. Complement factors play important roles in the mechanisms leading to sepsis and can potentially serve as early markers of sepsis and of sepsis severity and outcome. This review provides a synopsis of recent animal and clinical studies of the role of complement factors in sepsis development, together with their potential as disease markers. In addition, new results from our laboratory are presented regarding the involvement of the complement factor, mannose-binding lectin, in septic shock patients. Future clinical studies are needed to obtain the complete profiles of complement factors/their activated products during the course of sepsis development. We anticipate that the results of these studies will lead to a multipanel set of sepsis biomarkers which, along with currently used laboratory tests, will facilitate earlier diagnosis, timely treatment, and improved outcome.

Meningococcal disease and the complement system

Despite considerable advances in the understanding of the pathogenesis of meningococcal disease, this infection remains a major cause of morbidity and mortality globally. The role of the complement system in innate immune defenses against invasive meningococcal disease is well established. Individuals deficient in components of the alternative and terminal complement pathways are highly predisposed to invasive, often recurrent meningococcal infections. Genome-wide analysis studies also point to a central role for complement in disease pathogenesis. Here we review the pathophysiologic events pertinent to the complement system that accompany meningococcal sepsis in humans. Meningococci use several often redundant mechanisms to evade killing by human complement. Capsular polysaccharide and lipooligosaccharide glycan composition play critical roles in complement evasion. Some of the newly described protein vaccine antigens interact with complement components and have sparked considerable research interest.

Practice patterns of infectious disease physicians for management of meningococcal disease

BACKGROUND

Although empiric treatment regimens for acute bacterial meningitis are well established, there are many uncertainties regarding management of meningococcal disease. A survey was conducted among infectious disease specialists to assess meningococcal disease practice patterns and availability of antimicrobial susceptibility testing for Neisseria menigitidis.

METHODS

An online survey was distributed to 1342 pediatric and adult infectious disease specialists to assess common practices and opinions regarding the diagnosis, treatment and prevention of meningococcal disease. Specialists were also asked about the availability of antimicrobial susceptibility testing for Neisseria meningitidis at their clinical microbiology laboratory.

RESULTS

Six hundred fifty members responded to the survey (48%). Pediatric infectious disease specialists were more likely than adult specialists to use penicillin as definitive therapy for meningococcal disease (56% versus 46%; P = 0.038). Most pediatric specialists who would narrow therapy report that they would only switch to penicillin upon confirmation of penicillin susceptibility (55%), although 44% would narrow therapy based on a N. meningitidis species confirmation alone. More than one third of respondents reported that susceptibility testing for N. meningitidis is not routinely performed. There was also wide variation in complement deficiency screening criteria and meningococcal disease chemoprophylaxis practices among respondents.

CONCLUSIONS

Infectious disease specialists vary significantly in their practices regarding several aspects of meningococcal disease diagnosis, treatment and prevention. Antimicrobial susceptibility testing for N. meningitidis is not routinely performed in many practices. Consideration of these variations would be useful when developing treatment and prevention recommendations.

The role of complement system in septic shock

Septic shock is a critical clinical condition with a high mortality rate. A better understanding of the underlying mechanisms is important to develop effective therapies. Basic and clinical studies suggest that activation of complements in the common cascade, for example, complement component 3 (C3) and C5, is involved in the development of septic shock. The involvement of three upstream complement pathways in septic shock is more complicated. Both the classical and alternative pathways appear to be activated in septic shock, but the alternative pathway may be activated earlier than the classical pathway. Activation of these two pathways is essential to clear endotoxin. Recent investigations have shed light on the role of lectin complement pathway in septic shock. Published reports suggest a protective role of mannose-binding lectin (MBL) against sepsis. Our preliminary study of MBL-associated serine protease-2 (MASP-2) in septic shock patients indicated that acute decrease of MASP-2 in the early phase of septic shock might correlate with in-hospital mortality. It is unknown whether excessive activation of these three upstream complement pathways may contribute to the detrimental effects in septic shock. This paper also discusses additional complement-related pathogenic mechanisms and intervention strategies for septic shock.

Infections of people with complement deficiencies and patients who have undergone splenectomy

The complement system comprises several fluid-phase and membrane-associated proteins. Under physiological conditions, activation of the fluid-phase components of complement is maintained under tight control and complement activation occurs primarily on surfaces recognized as "nonself" in an attempt to minimize damage to bystander host cells. Membrane complement components act to limit complement activation on host cells or to facilitate uptake of antigens or microbes "tagged" with complement fragments. While this review focuses on the role of complement in infectious diseases, work over the past couple of decades has defined several important functions of complement distinct from that of combating infections. Activation of complement in the fluid phase can occur through the classical, lectin, or alternative pathway. Deficiencies of components of the classical pathway lead to the development of autoimmune disorders and predispose individuals to recurrent respiratory infections and infections caused by encapsulated organisms, including Streptococcus pneumoniae, Neisseria meningitidis, and Haemophilus influenzae. While no individual with complete mannan-binding lectin (MBL) deficiency has been identified, low MBL levels have been linked to predisposition to, or severity of, several diseases. It appears that MBL may play an important role in children, who have a relatively immature adaptive immune response. C3 is the point at which all complement pathways converge, and complete deficiency of C3 invariably leads to severe infections, including those caused by meningococci and pneumococci. Deficiencies of the alternative and terminal complement pathways result in an almost exclusive predisposition to invasive meningococcal disease. The spleen plays an important role in antigen processing and the production of antibodies. Splenic macrophages are critical in clearing opsonized encapsulated bacteria (such as pneumococci, meningococci, and Escherichia coli) and intraerythrocytic parasites such as those causing malaria and babesiosis, which explains the fulminant nature of these infections in persons with anatomic or functional asplenia. Paramount to the management of patients with complement deficiencies and asplenia is educating patients about their predisposition to infection and the importance of preventive immunizations and seeking prompt medical attention.

Relative importance of complement-mediated bactericidal and opsonic activity for protection against meningococcal disease

Killing of Neisseria meningitidis can result from complement-mediated serum bactericidal activity (SBA) or opsonophagocytosis (OPA), or a combination of the two mechanisms. While SBA titers > or =1:4 confer protection, recent evidence suggests that this threshold titer may not be required. For example, the incidence of meningococcal disease declines between ages 1 and 4 years without evidence of acquisition of SBA titers > or =1:4. Meningococcal polysaccharide vaccination also elicited OPA and lowered the risk of disease in patients with late complement component deficiencies whose sera did not support SBA. Sera from healthy adults immunized with an outer membrane vesicle vaccine showed OPA killing of N. meningitidis with C6-depleted complement, and whole blood from complement-sufficient non-immunized adults with SBA titers <1:4 also frequently had killing activity. Collectively the data indicate that SBA titers <1:4 and/or vaccine-induced OPA can confer protection against meningococcal disease.

Properdin deficiency associated with recurrent otitis media and pneumonia, and identification of male carrier with Klinefelter syndrome

Properdin is an initiator and stabilizer of the alternative complement activation pathway (AP). Deficiency of properdin is a rare X-linked condition characterized by increased susceptibility to infection with Neisseria meningitidis associated with a high mortality rate. We report properdin deficiency in a large Pakistani family. The index cases were found by screening for immunodeficiency due to a history of recurrent infections. This revealed absent AP activity, but normal classical and lectin pathway activity. Sequencing of the properdin gene (PFC) revealed a novel frameshift mutation. When all available relatives (n=24) were screened for the mutation, four affected males, four female carriers and a male heterozygous carrier were identified. He was subsequently diagnosed with Klinefelter syndrome. A questionnaire revealed a striking association between properdin deficiency and recurrent otitis media (P=0.0012), as well as recurrent pneumonia (P=0.0017). This study is the first to show a significant association between properdin deficiency and recurrent infections.

Investigation for complement deficiency following meningococcal disease

BACKGROUND AND AIMS

The incidence of complement abnormalities in the UK is not known. It is suggested in at least three major paediatric textbooks to test for abnormalities of the complement system following meningococcal disease (MCD).

METHODS

Over a four year period, surviving children with a diagnosis of MCD had complement activity assessed. A total of 297 children, aged 2 months to 16 years were screened.

RESULTS

All children except one had disease caused by B or C serogroups. One child, with group B meningococcal septicaemia (complicated by disseminated intravascular coagulation and who required ventilation and inotropic support) was complement deficient. C2 deficiency was subsequently diagnosed. She had other major pointers towards an immunological abnormality prior to her MCD.

CONCLUSION

It is unnecessary to screen all children routinely following MCD if caused by group B or C infection. However, it is important to assess the previous health of the child and to investigate appropriately if there have been previous suspicious infections, abnormal course of infective illnesses, or if this is a repeated episode of neisserial infection.

Update on meningococcal disease with emphasis on pathogenesis and clinical management

The only natural reservoir of Neisseria meningitidis is the human nasopharyngeal mucosa. Depending on age, climate, country, socioeconomic status, and other factors, approximately 10% of the human population harbors meningococci in the nose. However, invasive disease is relatively rare, as it occurs only when the following conditions are fulfilled: (i) contact with a virulent strain, (ii) colonization by that strain, (iii) penetration of the bacterium through the mucosa, and (iv) survival and eventually outgrowth of the meningococcus in the bloodstream. When the meningococcus has reached the bloodstream and specific antibodies are absent, as is the case for young children or after introduction of a new strain in a population, the ultimate outgrowth depends on the efficacy of the innate immune response. Massive outgrowth leads within 12 h to fulminant meningococcal sepsis (FMS), characterized by high intravascular concentrations of endotoxin that set free high concentrations of proinflammatory mediators. These mediators belonging to the complement system, the contact system, the fibrinolytic system, and the cytokine system induce shock and diffuse intravascular coagulation. FMS can be fatal within 24 h, often before signs of meningitis have developed. In spite of the increasing possibilities for treatment in intensive care units, the mortality rate of FMS is still 30%. When the outgrowth of meningococci in the bloodstream is impeded, seeding of bacteria in the subarachnoidal compartment may lead to overt meningitis within 24 to 36 h. With appropriate antibiotics and good clinical surveillance, the mortality rate of this form of invasive disease is 1 to 2%. The overall mortality rate of meningococcal disease can only be reduced when patients without meningitis, i.e., those who may develop FMS, are recognized early. This means that the fundamental nature of the disease as a meningococcus septicemia deserves more attention.

Update on meningococcal disease with emphasis on pathogenesis and clinical management

The only natural reservoir of Neisseria meningitidis is the human nasopharyngeal mucosa. Depending on age, climate, country, socioeconomic status, and other factors, approximately 10% of the human population harbors meningococci in the nose. However, invasive disease is relatively rare, as it occurs only when the following conditions are fulfilled: (i) contact with a virulent strain, (ii) colonization by that strain, (iii) penetration of the bacterium through the mucosa, and (iv) survival and eventually outgrowth of the meningococcus in the bloodstream. When the meningococcus has reached the bloodstream and specific antibodies are absent, as is the case for young children or after introduction of a new strain in a population, the ultimate outgrowth depends on the efficacy of the innate immune response. Massive outgrowth leads within 12 h to fulminant meningococcal sepsis (FMS), characterized by high intravascular concentrations of endotoxin that set free high concentrations of proinflammatory mediators. These mediators belonging to the complement system, the contact system, the fibrinolytic system, and the cytokine system induce shock and diffuse intravascular coagulation. FMS can be fatal within 24 h, often before signs of meningitis have developed. In spite of the increasing possibilities for treatment in intensive care units, the mortality rate of FMS is still 30%. When the outgrowth of meningococci in the bloodstream is impeded, seeding of bacteria in the subarachnoidal compartment may lead to overt meningitis within 24 to 36 h. With appropriate antibiotics and good clinical surveillance, the mortality rate of this form of invasive disease is 1 to 2%. The overall mortality rate of meningococcal disease can only be reduced when patients without meningitis, i.e., those who may develop FMS, are recognized early. This means that the fundamental nature of the disease as a meningococcus septicemia deserves more attention.

Septic shock

Although our understanding of molecular events in septic shock is growing exponentially, bedside management has changed only incrementally over the last 20 years. In pediatric and adult patients alike, treatment continues to be largely supportive. Morbidity and mortality, though gradually improving, continue to be high. The major similarities, as well as the minor differences, between pediatric and adult septic shock are reviewed in this article, with an emphasis on current clinical practice and recent clinical investigations of novel therapies.

Etiology and treatment of acquired coagulopathies in the critically ill adult and child

Excessive bleeding frequently complicates the care of critically ill patients. Except in the case of trauma or inpatients with known coagulopathies, the bleeding is generally not directly related to the illness that results in admission to the intensive care unit. In general, the causes of the bleeding can be divided into three categories: consumptive coagulopathies, bleeding related to "hepatic issues," and iatrogenic causes. In most circumstances, the pathogenesis and management of these acquired coagulopathies do not differ between the adult and child patient. However, some differences do exist in regards to the clinical manifestations and management of some consumptive coagulopathies. This article reviews the more common causes of bleeding in the critically ill patient and outlines diagnostic and treatment approaches for these patients. Particular emphasis will be placed on the differences in presentation and management where differences exist.