Homozygous deficiency of the second component of complement presenting with recurrent bacterial meningitis

The genetic basis of pneumococcal and staphylococcal infections: inborn errors of human TLR and IL-1R immunity

Many bacteria can cause pyogenic lesions in humans. Most of these bacteria are harmless in most individuals, but they, nevertheless, cause significant morbidity and mortality worldwide. The inherited and acquired immunodeficiencies underlying these pyogenic infections differ between bacteria. This short review focuses on two emblematic pyogenic bacteria: pneumococcus (Streptococcus pneumoniae) and Staphylococcus, both of which are Gram-positive encapsulated bacteria. We will discuss the contribution of human genetic studies to the identification of germline mutations of the TLR and IL-1R pathways.

IRAK4 and NEMO mutations in otherwise healthy children with recurrent invasive pneumococcal disease

BACKGROUND

About 2% of childhood episodes of invasive pneumococcal disease (IPD) are recurrent, and most remain unexplained.

OBJECTIVE

To report two cases of otherwise healthy, unrelated children with recurrent IPD as the only clinical infectious manifestation of an inherited disorder in nuclear factor-kappaB(NF-kappaB)-dependent immunity.

RESULTS

One child carried two germline mutations in IRAK4, and had impaired cellular responses to interleukin (IL)1 receptor and toll-like receptor (TLR) stimulation. The other child carried a hemizygous mutation in NEMO, associated with a broader impairment of NF-kappaB activation, with an impaired cellular response to IL-1R, TLR and tumour necrosis factor receptor stimulation. The two patients shared a narrow clinical phenotype, associated with two related but different genotypes.

CONCLUSIONS

Otherwise healthy children with recurrent IPD should be explored for underlying primary immunodeficiencies affecting the IRAK4-dependent and NEMO-dependent signalling pathways.

Early manifestation and recognition of C2 complement deficiency in the form of pyogenic infection in infancy

OBJECTIVE

Although frequently asymptomatic, C2 complement component deficiency may lead to severe pyogenic infections or lupus-like illness. In the present report, we describe infectious manifestations in infancy and childhood in our C2-deficient patients.

METHOD

A retrospective study of clinical manifestation in three patients was carried out. C2 deficiency was proved both by undetectable serum C2 level and typical homozygous 28 bp deletion of the C2 gene.

RESULTS

All patients were hospitalized at least once by the age of 12 months, each had one episode of meningitis in infancy, one also had arthritis with septicaemia. Infections of the respiratory tract were the causes of other hospitalizations. Two patients also suffered from frequent mild respiratory tract infections; in both patients, decreased immunoglobulin IgA and immunoglobulin IgG2 or immunoglobulin IgG3 levels were recorded.

CONCLUSION

Our observations point to an early manifestation of C2 deficiency within the first year of life, with meningitis as the most severe complication. The severity of immunodeficiency may be influenced by concomitant deficiencies of immunoglobulin isotypes.

Recurrent bacterial meningitis

To characterize recurrent bacterial meningitis in children, we reviewed the charts of all patients treated for more than one episode of bacterial meningitis at the Würzburg University Children's Hospital from 1980 to June 1995. Twenty-five children suffered 2-13 episodes of bacterial meningitis. Most patients were referred from other hospitals to our paediatric neurosurgical service. No immunodeficiency was found. In all patients, the cause of recurrent meningitis was an anatomical lesion with 13 intracranial defects including encephaloceles, skull fractures, Mondini dysplasias, neurenteric cyst, fibrous dysplasia, persistent craniopharyngeal duct, and 12 lumboscral defects with a dermoid cyst within the lumbosacral spine. A first episode of meningitis at school age did not exclude a congenital defect. In total, 84 episodes of meningitis were treated, a pathogen was isolated in 77%. The most common pathogen was Streptococcus pneumoniae, followed by Escherichia coli, Staphylococci and others. The pathogen isolated often gave a clue to the location of the defect. Personal history was often unrewarding and in some cases the search for the anatomical lesion required repeated imaging and explorative surgery. In 24 of 25 cases, final treatment of recurrent meningitis was by surgical intervention.

CONCLUSION

In recurrent bacterial meningitis, excessive diagnostic and therapeutic procedures are indicated. An anatomical defect is a very probable cause.

Bacterial meningitis in children. Selected aspects

Accumulating clinical experience has gradually outlined the epidemiology of acute bacterial meningitis, including the epidemic and the sporadic forms, the customary clinical signs related to different age groups and causative organisms, and methods of rapid diagnosis by laboratory examinations. Effective treatment, which continues to evolve, emerged in the 1940s with the development of antibacterial antimicrobials, first with the sulfonamides and then with the penicillins. The literature relative to these aspects of the disease has been abundant in the past few years. This article is directed to a variety of topics that have direct bearing on the disorder but are less often addressed to those who deal with infants and children.

Defective activation of the alternative pathway of complement in patients with homozygous C2 deficiency: studies in two unrelated families

Selective homozygous deficiency of the second component of complement, C2, with increased susceptibility to infection was detected in five children of two unrelated families. Because the haemolytic activity of the alternative complement pathway (AP) was in the low normal range, we evaluated the AP activation pattern. Serum levels of factor B measured immunochemically and the haemolytic function of factor B were low normal. Levels of C3d were not increased. Activation products of factor B were undetectable indicating the absence of in vivo activation of AP. Activation of C3 in vitro by activators of the AP (zymosan A and lipopolysaccharide) was profoundly deficient in homozygous C2 deficiency while heterozygous carriers exhibited intermediate values. There was no correlation between serum levels of factor B and in vitro C3 activation. We conclude that defective AP activation may contribute to increased susceptibility to bacterial infections in some patients with homozygous C2 deficiency.

Infectious diseases associated with complement deficiencies

The complement system consists of both plasma and membrane proteins. The former influence the inflammatory response, immune modulation, and host defense. The latter are complement receptors, which mediate the cellular effects of complement activation, and regulatory proteins, which protect host cells from complement-mediated injury. Complement activation occurs via either the classical or the alternative pathway, which converge at the level of C3 and share a sequence of terminal components. Four aspects of the complement cascade are critical to its function and regulation: (i) activation of the classical pathway, (ii) activation of the alternative pathway, (iii) C3 convertase formation and C3 deposition, and (iv) membrane attack complex assembly and insertion. In general, mechanisms evolved by pathogenic microbes to resist the effects of complement are targeted to these four steps. Because individual complement proteins subserve unique functional activities and are activated in a sequential manner, complement deficiency states are associated with predictable defects in complement-dependent functions. These deficiency states can be grouped by which of the above four mechanisms they disrupt. They are distinguished by unique epidemiologic, clinical, and microbiologic features and are most prevalent in patients with certain rheumatologic and infectious diseases. Ethnic background and the incidence of infection are important cofactors determining this prevalence. Although complement undoubtedly plays a role in host defense against many microbial pathogens, it appears most important in protection against encapsulated bacteria, especially Neisseria meningitidis but also Streptococcus pneumoniae, Haemophilus influenzae, and, to a lesser extent, Neisseria gonorrhoeae. The availability of effective polysaccharide vaccines and antibiotics provides an immunologic and chemotherapeutic rationale for preventing and treating infection in patients with these deficiencies.

Deficiency of IgG subclasses and IgA, and elevation of IgE in children with a past history of bacterial meningitis

Of 44 children who recovered from an attack of bacterial meningitis, 3 (7%) were found to have IgG subclass deficiency, 5 (11%) had IgA deficiency and 22 (50%) had raised IgE levels. These results suggest that immunoglobulin abnormalities may be an important predisposing factor in some cases of bacterial meningitis.

Recurrent meningitis: a case report

A 25-month-old girl is described who experienced three successive attacks of purulent meningitis due to Proteus mirabilis. Third generation cephalosporins were employed as treatment. Cranial radiography and computed tomography revealed a malformation, in the form of an epidermoid cyst, in a central occipital position; small cerebellar abscesses were also present. The lesion was removed by surgery which led to a complete recovery.

The role of natural agglutinins and trypanolytic activity in host specificity of Trypanosoma musculi

Trypanolytic activity and agglutinins for T. musculi were demonstrated in sera from refractory hosts. The agglutinins in human and bovine serum were specific antibodies. The trypanolytic activity was a result of the ability of the trypanosomes to activate complement in these normal sera. The results suggested that Trypanosoma musculi activates human complement by the alternative pathway. The activity was inhibited by EDTA but not EGTA, and trypanosome lysis occurred in the absence of C2. In addition, conversion of C3 occurred in the presence of EGTA. The trypanolytic activity of bovine serum was similarly inhibited by EDTA but not EGTA. Trypanosome lysis failed to occur in C6 deficient rabbit serum, showing that the late components of complement are required for parasite lysis. Trypanosome lysis by human or bovine serum was inhibited by the addition of mouse serum but not rat serum. These observations suggest that the presence of trypanolytic activity and antibodies to this trypanosome in sera of normal mammals may be responsible for the restricted host range of the trypanosome, and that the absence of these antibodies and the ability of this parasite to evade the trypanolytic activity enables T. musculi to establish infections in the mouse.

Activation of human complement by the pneumococcal toxin pneumolysin

Highly purified pneumolysin (at a concentration of 10 micrograms/ml) caused significant activation of human complement, as measured by conversion of C3. Complement activation in the presence of pneumolysin was not observed in sera chelated with a combination of Mg2+ and ethylene glycol-bis(beta-aminoethyl ether)-N,N-tetraacetic acid, and activation was only slight in C2-deficient sera. This suggests that the toxin is capable of activating the classical complement pathway. Treatment of normal human serum with pneumolysin also significantly reduced its opsonic activity for Streptococcus pneumoniae.

Complement and the host's defense against the pneumococcus

The complement system plays a critical role in resistance to Streptococcus pneumoniae. In the last two decades, a great deal of new knowledge has been generated on both the complement system and on the pneumococcus. Not only has this new knowledge helped produce a better understanding of how the complement system serves the host in its defense against S. pneumoniae, but in a more general fashion, the lessons learned from the interaction of complement and the pneumococcus have also provided insight into how the complement system functions in the defense of the host against a wide variety of other microorganisms. The following review will attempt to summarize current knowledge about the complement system, how it interacts at the molecular level with the pneumococcus, the biologic consequences of that interaction, and their significance in pneumococcal infections.

Inherited disorders of complement

Isolated complement component deficiencies are uncommon. Deficiencies of all eleven components and two inhibitors of the classical pathway have been described. Complete absence of the components of the alternative pathway has not been described. The consequences of a single defect in complement are often predictable from an understanding of the biologic activities associated with activation of the complement system. Deficiency of C1 esterase inhibitor gives rise to the disease, hereditary angioedema; deficiency of the early components of the classical pathway are associated with lupus erythematosus; C3 and C3 inactivator deficiencies with pyogenic infections; C5 dysfunction with Leiner's disease; deficiencies of the terminal components with recurrent Neisseria bacteremia; and C9 deficiency with normal health. The complement system and its associated biologic activities are reviewed. The present knowledge of the inherited complement deficiencies and associated diseases, with particular emphasis on the dermatologic manifestations, genetics, and diagnosis, is summarized.

Activation of the alternative pathway of complement by Acanthamoeba culbertsoni

Normal human serum (NHS) contained an amoebicidal property for Acanthamoeba culbertsoni. Killing was quantitated by measuring the ability of the amoebae to undergo cell division subsequent to exposure to NHS, and also by microscopical examination. Plasma membrane disruption and extrusion of intracellular components occurred within 5-10 min following exposure to NHS. Adsorption of specific antibody did not remove the amoebicidal activity while heating serum at 56 degrees C/30 min or treatment with zymosan prevented the killing of A. culbertsoni. Haemolytic complement was consumed and C3 conversion occurred during the incubation of NHS with amoebae. Killing required the presence of the late complement components. The findings that (a) amoebae were killed in C2 deficient human serum and ethylene glycol tetra-acetic acid (EGTA), but not ethylenediamine tetra-acetic acid (EDTA) treated NHS; (b) haemolytic complement consumption, which occurred by incubating NHS with the amoebae, could be prevented by addition of EDTA, but not EGTA and (c) conversion of C3 occurred in the presence of EGTA, but not EDTA, indicated that activation of the alternative pathway of complement was involved. This may be of importance as a natural defence mechanism in humans against A. culbertsoni infections.

Alternative pathway activation of complement by African trypanosomes lacking a glycoprotein coat

An in vitro culture Trypanosoma congolense cell line was established using the mammalian cell feeder layer system. One of the principle characteristics of this parasite was its ability to multiply in culture at 35 degrees C, as an uncoated trypanosome (lacking a glycoprotein surface coat) unlike the original blood stream form from which it was derived. This trypanosome was lysed when incubated in normal human serum in contrast to the parasite which possessed a surface coat. The lytic reaction as inhibited by EDTA but not EGTA and occurred in C2-deficient serum, demonstrating the involvement of the alternative pathway of complement activation. Similar results were obtained with procyclic forms of T. congolense and T. brucei brucei which also lacked surface coats. The results suggest that the glycoprotein surface coat protects the parasite by masking sites on the plasma membrane which are capable of promoting alternative pathway activation.

Genetic deficiency of C4 presenting with recurrent infections and a SLE-like disease. Genetic and immunologic studies

A young girl presenting with recurrent pulmonary infections and atypical lupus erythematosus was totally deficient in C4. In one sister, also deficient in C4, the same symptoms developed. Results of family studies were consistent with an autosomal recessive mode of transmission and with linkage of the genes determining C4 deficiency to those of the major histocompatibility complex. The patient's serum and red cells were Chido- and Rodgers-negative. Humoral and cellular immunity were normal, except for a low lymphocyte response in mixed lymphocyte culture. The cellular function of the patient's polymorphonuclear leukocytes was normal, for both phagocytosis and bactericidal activity using Candida albicans. However, in the presence of C4-deficient serum, opsonin generation and bactericidal indexes were diminished. These defects were completely reversible upon addition of purified C4.

Recurrent pyogenic infections in individuals with absence of the second component of complement

While deficiency of the terminal components of complement (C3-C8) has classically been associated with recurrent pyogenic infections, it has become apparent that C2 deficiency is also associated with recurrent infections in some individuals. The patient presented here had two major pyogenic infections prior to 1 year of age and was found to lack the second component of complement. Studies of alternative complement pathway and humoral and cellular immunity were found to be within normal limits. Family studies suggest an autosomal codominant pattern of inheritance for the C2 defect, which also corresponded to the inheritance of the HLA A10 B18 haplotype. A review of the literature revealed nine other cases of C2-deficient patients with well-documented recurrent infections. In these patients, Streptococcus pneumoniae is the organism most frequently implicated in infectious processes, whether or not their alternative complement pathway is intact.

Differential complement resistance mediates virulence of Haemophilus influenzae type b

Studies were undertaken to gain insight into the virulence of type b in contrast to the other Haemophilus influenzae capsular types. A relationship was found between the comparative virulence of H. influenzae types in humans and their resistance to the bactericidal effect of antibody-free complement. Type b was most resistant to the bactericidal effect of complement. The other types could be divided into three groups based upon their susceptibility to complement; this grouping was also related to their structural similarities. No association between virulence and either the biotype, source of isolate, in vitro association with peripheral polymorphonuclear leukocytes, or the total amount of capsular polysaccharide was found. However, among the type b strains, higher levels of cell-associated polysaccharide were associated with increased resistance to complement. The relative virulence of the six H. influenzae types in the infant rat model was generally similar to that in humans. After intraperitoneal challenge, type b and type a strains had the lowest 50% effective doses for bacteremia, removed by several logs from the values of the other types. By intranasal challenge, type b strains produced higher rates and levels of bacteremia than did type a strains. High levels of natural bactericidal antibodies to types c and e were found in adult female rats; this finding alone could not account for the differences in virulence among the H. influenzae types in the infant rat model. We propose that the virulence of type b strains is due to their greater resistance to the bactericidal activity of serum complement alone. Resistance to type b disease requires serum antibody to induce the complement-mediated reaction.

Immunological competence of children with pyogenic meningitis

A broad range of immunological tests was performed on 9 consecutive children with pyrogenic meningitis. Two were found to have combined IgG and IgA deficiency. One had a combination of IgG deficiency and impaired neutrophil chemotaxis. Primary immunodeficiency disorders as a predisposing cause of pyogenic meningitis may be more common than previously suspected.

Immunocompetence of children with frequent respiratory infections

119 children with recurrent respiratory infections were investigated for immunocompetence. They were divided into two groups. The first, group A, comprised children who had had predominantly upper respiratory infections. Group B comprised those who had had repeated pneumonia in addition. The groups were comparable for gender and age (mean 4.2 years). All the children had reduced neutrophil chemotaxis, reduced neutrophil fungicidal capacity, and perhaps reduced T-cell percentages. Group B children had, in addition to the above, decreased neutrophil bactericidal capacity and a more marked depression of neutrophil chemotaxis. In both groups, some children had reduced immunoglobulin concentrations while others had either normal or increased concentrations. Serum complement, neutrophil iodination, and mitogen-induced lymphocyte transformation were comparable with adult controls in both groups.