Deficiency of the fifth component of complement in human subjects. Clinical, genetic and immunologic studies in a large kindred

A Meta-analysis to Quantify the Risk of Disseminated Gonococcal Infection With Porin B Serotype

The escalating rates of gonorrhea globally are associated with higher numbers of disseminated gonococcal infection (DGI). Expression of the PorB1A allele of the major outer membrane porin protein, PorB, is associated with DGI. This meta-analysis shows that the odds of PorB1A strains to disseminate is 20.53 compared to PorB1B isolates.

An optimized Factor H-Fc fusion protein against multidrug-resistant Neisseria gonorrhoeae

Novel therapeutics against the global threat of multidrug-resistant Neisseria gonorrhoeae are urgently needed. Gonococci evade killing by complement by binding factor H (FH), a key inhibitor of the alternative pathway. FH comprises 20 short consensus repeat (SCR) domains organized as a single chain. Gonococci bind FH through domains 6 and 7, and C-terminal domains 18 through 20. Previously, we showed that a chimeric protein comprising (from the N- to C-terminus) FH domains 18-20 (containing a point mutation in domain 19 to prevent lysis of host cells) fused to human IgG1 Fc (called FH*/Fc1) killed gonococci in a complement-dependent manner and reduced the duration and bacterial burden in the mouse vaginal colonization model of gonorrhea. Considering the N. gonorrhoeae-binding FH domains 18-20 are C-terminal in native FH, we reasoned that positioning Fc N-terminal to FH* (Fc1/FH*) would improve binding and bactericidal activity. Although both molecules bound gonococci similarly, Fc1/FH* displayed a 5-fold lower IC50 (the concentration required for 50% killing in complement-dependent bactericidal assays) than FH*/Fc1. To further increase complement activation, we replaced human IgG1 Fc in Fc1/FH* with Fc from human IgG3, the most potent complement-activating IgG subclass, to obtain Fc3/FH*. Bactericidal activity was further increased ~2.3-fold in Fc3/FH* compared to Fc1/FH*. Fc3/FH* killed (defined by <50% survival) 45/45 (100%) diverse PorB1B-expessing gonococci, but only 2/15 PorB1A-expressing isolates, in a complement-dependent manner. Decreased Fc3/FH* binding accounted for the limited activity against PorB1A strains. Fc3/FH* was efficacious against all four tested PorB1B gonococcal strains in the mouse vaginal colonization model when administered at a dose of 5 µg intravaginally, daily. Furthermore, Fc3/FH* retained bactericidal activity when reconstituted following lyophilization or spray-drying, suggesting feasibility for formulation into intravaginal rings. In conclusion, Fc3/FH* represents a promising prophylactic immunotherapeutic against multidrug-resistant gonococci.

Development of Complement Factor H-Based Immunotherapeutic Molecules in Tobacco Plants Against Multidrug-Resistant Neisseria gonorrhoeae

Novel therapeutics against the global threat of multidrug-resistant Neisseria gonorrhoeae are urgently needed. Gonococci possess several mechanisms to evade killing by human complement, including binding of factor H (FH), a key inhibitor of the alternative pathway. FH comprises 20 short consensus repeat (SCR) domains organized in a head-to-tail manner as a single chain. N. gonorrhoeae binds two regions in FH; domains 6 and 7 and domains 18 through 20. We designed a novel anti-infective immunotherapeutic molecule that fuses domains 18-20 of FH containing a D-to-G mutation in domain 19 at position 1119 (called FH*) with human IgG1 Fc. FH*/Fc retained binding to gonococci but did not lyse human erythrocytes. Expression of FH*/Fc in tobacco plants was undertaken as an alternative, economical production platform. FH*/Fc was expressed in high yields in tobacco plants (300-600 mg/kg biomass). The activities of plant- and CHO-cell produced FH*/Fc against gonococci were similar in vitro and in the mouse vaginal colonization model of gonorrhea. The addition of flexible linkers [e.g., (GGGGS)2 or (GGGGS)3] between FH* and Fc improved the bactericidal efficacy of FH*/Fc 2.7-fold. The linkers also improved PMN-mediated opsonophagocytosis about 11-fold. FH*/Fc with linker also effectively reduced the duration and burden of colonization of two gonococcal strains tested in mice. FH*/Fc lost efficacy: i) in C6-/- mice (no terminal complement) and ii) when Fc was mutated to abrogate complement activation, suggesting that an intact complement was necessary for FH*/Fc function in vivo. In summary, plant-produced FH*/Fc represent promising prophylactic or adjunctive immunotherapeutics against multidrug-resistant gonococci.

Complement-Dependent Serum Bactericidal Assays for Neisseria gonorrhoeae

The global spread of multidrug-resistant gonorrhea has spurred efforts to develop a safe and effective vaccine against gonorrhea. Complement plays an important role in host defenses against Neisseria infections. Complement-dependent bactericidal activity of antibodies (either natural antibodies or those elicited by immunization) is a well-established correlate of protection against meningococcal infections. Although correlates of protection against gonococcal infection have not been defined, there is evidence to suggest that complement-mediated killing may also predict vaccine efficacy against this disease. This chapter describes methods to prepare human complement sources and perform bactericidal assays against Neisseria gonorrhoeae.

Human genetics of meningococcal infections

Neisseria meningitidis is a leading cause of bacterial septicaemia and meningitis worldwide. Meningococcal disease is rare but can be life threatening with a tendency to affect children. Many studies have investigated the role of human genetics in predisposition to N. meningitidis infection. These have identified both rare single-gene mutations as well as more common polymorphisms associated with meningococcal disease susceptibility and severity. These findings provide clues to the pathogenesis of N. meningitidis, the basis of host susceptibility to infection and to the aetiology of severe disease. From the multiple discoveries of monogenic complement deficiencies to the associations of complement factor H and complement factor H-related three polymorphisms to meningococcal disease, the complement pathway is highlighted as being central to the genetic control of meningococcal disease. This review aims to summarise the current understanding of the host genetic basis of meningococcal disease with respect to the different stages of meningococcal infection.

Preclinical Efficacy of a Lipooligosaccharide Peptide Mimic Candidate Gonococcal Vaccine

The global spread of multidrug-resistant strains of Neisseria gonorrhoeae constitutes a public health emergency. With limited antibiotic treatment options, there is an urgent need for development of a safe and effective vaccine against gonorrhea. Previously, we constructed a prototype vaccine candidate comprising a peptide mimic (mimitope) of a glycan epitope on gonococcal lipooligosaccharide (LOS), recognized by monoclonal antibody 2C7. The 2C7 epitope is (i) broadly expressed as a gonococcal antigenic target in human infection, (ii) a critical requirement for gonococcal colonization in the experimental setting, and (iii) a virulence determinant that is maintained and expressed by gonococci. Here, we have synthesized to >95% purity through a relatively facile and economical process a tetrapeptide derivative of the mimitope that was cyclized through a nonreducible thioether bond, thereby rendering the compound homogeneous and stable. This vaccine candidate, called TMCP2, when administered at 0, 3, and 6 weeks to BALB/c mice at either 50, 100 or 200 μg/dose in combination with glucopyranosyl lipid A-stable oil-in-water nanoemulsion (GLA-SE; a Toll-like receptor 4 and T_H1-promoting adjuvant), elicited bactericidal IgG and reduced colonization levels of gonococci in experimentally infected mice while accelerating clearance by each of two different gonococcal strains. Similarly, a 3-dose biweekly schedule (50 μg TMCP2/dose) was also effective in mice. We have developed a gonococcal vaccine candidate that can be scaled up and produced economically to a high degree of purity. The candidate elicits bactericidal antibodies and is efficacious in a preclinical experimental infection model.IMPORTANCE Neisseria gonorrhoeae has become resistant to most antibiotics. The incidence of gonorrhea is also sharply increasing. A safe and effective antigonococcal vaccine is urgently needed. Lipooligosaccharide (LOS), the most abundant outer membrane molecule, is indispensable for gonococcal pathogenesis. A glycan epitope on LOS that is recognized by monoclonal antibody (MAb) 2C7 (called the 2C7 epitope) is expressed almost universally by gonococci in vivo Previously, we identified a peptide mimic (mimitope) of the 2C7 epitope, which when configured as an octamer and used as an immunogen, attenuated colonization of mice by gonococci. Here, a homogenous, stable tetrameric derivative of the mimitope, when combined with a T_H1-promoting adjuvant and used as an immunogen, also effectively attenuates gonococcal colonization of mice. This candidate peptide vaccine can be produced economically, an important consideration for gonorrhea, which affects socioeconomically underprivileged populations disproportionately, and represents an important advance in the development of a gonorrhea vaccine.

Human inborn errors of immunity to infection affecting cells other than leukocytes: from the immune system to the whole organism

Studies of vertebrate immunity have traditionally focused on professional cells, including circulating and tissue-resident leukocytes. Evidence that non-professional cells are also intrinsically essential (i.e. not via their effect on leukocytes) for protective immunity in natural conditions of infection has emerged from three lines of research in human genetics. First, studies of Mendelian resistance to infection have revealed an essential role of DARC-expressing erythrocytes in protection against Plasmodium vivax infection, and an essential role of FUT2-expressing intestinal epithelial cells for protection against norovirus and rotavirus infections. Second, studies of inborn errors of non-hematopoietic cell-extrinsic immunity have shown that APOL1 and complement cascade components secreted by hepatocytes are essential for protective immunity to trypanosome and pyogenic bacteria, respectively. Third, studies of inborn errors of non-hematopoietic cell-intrinsic immunity have suggested that keratinocytes, pulmonary epithelial cells, and cortical neurons are essential for tissue-specific protective immunity to human papillomaviruses, influenza virus, and herpes simplex virus, respectively. Various other types of genetic resistance or predisposition to infection in human populations are not readily explained by inborn variants of genes operating in leukocytes and may, therefore, involve defects in other cells. The probing of this unchartered territory by human genetics is reshaping immunology, by scaling immunity to infection up from the immune system to the whole organism.

Complement alone drives efficacy of a chimeric antigonococcal monoclonal antibody

Multidrug-resistant Neisseria gonorrhoeae is a global health problem. Monoclonal antibody (mAb) 2C7 recognizes a gonococcal lipooligosaccharide epitope that is expressed by >95% of clinical isolates and hastens gonococcal vaginal clearance in mice. Chimeric mAb 2C7 (human immunoglobulin G1 [IgG1]) with an E430G Fc modification that enhances Fc:Fc interactions and hexamerization following surface-target binding and increases complement activation (HexaBody technology) showed significantly greater C1q engagement and C4 and C3 deposition compared to mAb 2C7 with wild-type Fc. Greater complement activation by 2C7-E430G Fc translated to increased bactericidal activity in vitro and, consequently, enhanced efficacy in mice, compared with “Fc-unmodified” chimeric 2C7. Gonococci bind the complement inhibitors factor H (FH) and C4b-binding protein (C4BP) in a human-specific manner, which dampens antibody (Ab)-mediated complement-dependent killing. The variant 2C7-E430G Fc overcame the barrier posed by these inhibitors in human FH/C4BP transgenic mice, for which a single 1 μg intravenous dose cleared established infection. Chlamydia frequently coexists with and exacerbates gonorrhea; 2C7-E430G Fc also proved effective against gonorrhea in gonorrhea/chlamydia-coinfected mice. Complement activation alone was necessary and sufficient for 2C7 function, evidenced by the fact that (1) “complement-inactive” Fc modifications that engaged Fc gamma receptor (FcγR) rendered 2C7 ineffective, nonetheless; (2) 2C7 was nonfunctional in C1q^−/− mice, when C5 function was blocked, or in C9^−/− mice; and (3) 2C7 remained effective in neutrophil-depleted mice and in mice treated with PMX205, a C5a receptor (C5aR1) inhibitor. We highlight the importance of complement activation for antigonococcal Ab function in the genital tract. Elucidating the correlates of protection against gonorrhea will inform the development of Ab-based gonococcal vaccines and immunotherapeutics.

A chimeric antibody that contains a "complement-enhancing" mutation in Fc (so-called HexaBody technology) shows increased bactericidal activity compared to antibody bearing wild-type Fc and may represent a promising immunotherapeutic approach against multidrug-resistant gonorrhea.

Severe infectious diseases of childhood as monogenic inborn errors of immunity

This paper reviews the developments that have occurred in the field of human genetics of infectious diseases from the second half of the 20th century onward. In particular, it stresses and explains the importance of the recently described monogenic inborn errors of immunity underlying resistance or susceptibility to specific infections. The monogenic component of the genetic theory provides a plausible explanation for the occurrence of severe infectious diseases during primary infection. Over the last 20 y, increasing numbers of life-threatening infectious diseases striking otherwise healthy children, adolescents, and even young adults have been attributed to single-gene inborn errors of immunity. These studies were inspired by seminal but neglected findings in plant and animal infections. Infectious diseases typically manifest as sporadic traits because human genotypes often display incomplete penetrance (most genetically predisposed individuals remain healthy) and variable expressivity (different infections can be allelic at the same locus). Infectious diseases of childhood, once thought to be archetypal environmental diseases, actually may be among the most genetically determined conditions of mankind. This nascent and testable notion has interesting medical and biological implications.

A simple PCR-based method for the rapid genotyping of inherited fifth complement component (C5)-deficient mice

The fifth component of complement (C5) is considered to be the center of complement activation and function. However, there are no genetically engineered knockout mice for this gene, and the only commercially available inherited C5-deficient mice, in which a “TA” nucleotide deletion in the coding frame was previously identified, are in theC57BL/10Sn genetic background rather than the commonly used backgrounds C57BL/6 and BALB/c. Therefore, these mice must be backcrossed into the desired genetic background. Here, we developed an ARMS (amplification refractory mutation system) PCR method using a specific primer pair that was able to discriminate between the genotypes when the resulting product was analyzed by agarose gel electrophoresis. These results were supported by quantitative RT-PCR and semi-quantitative PCR and were consistent with the results from sequencing each backcrossed generation. Using ARMS-PCR method, we generated C5-deficient mice in the C57BL/6 background over 9 backcrossed generations and further verified the phenotype using complement-mediated hemolytic assays. In this study, we describe a simple, rapid and reliable PCR-based method for genotyping inherited C5-deficient mice that may be used to backcross C57BL/10Sn mice into other genetic backgrounds.

C5 complement deficiency in a Saudi family, molecular characterization of mutation and literature review

INTRODUCTION

Complement deficiencies are rare primary immunodeficiency disorders, the diagnosis of which is often underestimated. Only a small number of molecular studies have been carried out for the characterization of the underlying genetic defects in these cases.

PURPOSE

Reporting the first family from the Arabian Gulf region with multiple members affected by meningococcemia and abscent serum complement 5 (C5). We tried to correlate clinical, biochemical and molecular genetics features of this family.

METHODS

Determination of the serum level of all complement proteins including the terminal cascade (C5-9), followed by mutation analysis on DNA extracted from fresh blood samples of each alive family member.

RESULTS

Molecular studies showed a homozygous nonsense mutation in exon 1, with the change of cytosine to thymine at position 55 (55C > T) leading to change of the glutamine amino acid at position 19 to a stop codon (Q19X), and serologically absence of C5 in the serum. A similar but compound heterozygous mutation has been reported in one African-American family. previously.

CONCLUSION

Characterization of the underlying mutations in C5 deficient families is important, to understand this uncommon complement deficiency, and try to elucidate structure-function relationships in the C5 gene. This report also highlights the importance of complement screening in cases of sporadic meningococcal Infections, especially in communities with high prevalence of consanguineous marriages, which will ensure timely and adequate clinical interventions.

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.

Factor H Binding and Function in Sialylated Pathogenic Neisseriae is Influenced by Gonococcal, but Not Meningococcal, Porin

Neisseria gonorrhoeae and Neisseria meningitidis both express the lacto-N-neotetraose (LNT) lipooligosaccharide (LOS) molecule that can be sialylated. Although gonococcal LNT LOS sialylation enhances binding of the alternative pathway complement inhibitor factor H and renders otherwise serum-sensitive bacteria resistant to complement-dependent killing, the role of LOS sialylation in meningococcal serum resistance is less clear. We show that only gonococcal, but not meningococcal, LNT LOS sialylation enhanced factor H binding. Replacing the porin (Por) B molecule of a meningococcal strain (LOS sialylated) that did not bind factor H with gonococcal Por1B augmented factor H binding. Capsule expression did not alter factor H binding to meningococci that express gonococcal Por. Conversely, replacing gonococcal Por1B with meningococcal PorB abrogated factor H binding despite LNT LOS sialylation. Gonococcal Por1B introduced in the background of an unsialylated meningococcus itself bound small amounts of factor H, suggesting a direct factor H-Por1B interaction. Factor H binding to unsialylated meningococci transfected with gonococcal Por1B was similar to the sialylated counterpart only in the presence of higher (20 microg/ml) concentrations of factor H and decreased in a dose-responsive manner by approximately 80% at 1.25 microg/ml. Factor H binding to the sialylated strain remained unchanged over this factor H concentration range however, suggesting that LOS sialylation facilitated optimal factor H-Por1B interactions. The functional counterpart of factor H binding showed that sialylated meningococcal mutants that possessed gonococcal Por1B were resistant to complement-mediated killing by normal human serum. Our data highlight the different mechanisms used by these two related species to evade complement.

Familial chilblain lupus, a monogenic form of cutaneous lupus erythematosus, maps to chromosome 3p

Systemic lupus erythematosus is a prototypic autoimmune disease. Apart from rare monogenic deficiencies of complement factors, where lupuslike disease may occur in association with other autoimmune diseases or high susceptibility to bacterial infections, its etiology is multifactorial in nature. Cutaneous findings are a hallmark of the disease and manifest either alone or in association with internal-organ disease. We describe a novel genodermatosis characterized by painful bluish-red inflammatory papular or nodular lesions in acral locations such as fingers, toes, nose, cheeks, and ears. The lesions sometimes appear plaquelike and tend to ulcerate. Manifestation usually begins in early childhood and is precipitated by cold and wet exposure. Apart from arthralgias, there is no evidence for internal-organ disease or an increased susceptibility to infection. Histological findings include a deep inflammatory infiltrate with perivascular distribution and granular deposits of immunoglobulins and complement along the basement membrane. Some affected individuals show antinuclear antibodies or immune complex formation, whereas cryoglobulins or cold agglutinins are absent. Thus, the findings are consistent with chilblain lupus, a rare form of cutaneous lupus erythematosus. Investigation of a large German kindred with 18 affected members suggests a highly penetrant trait with autosomal dominant inheritance. By single-nucleotide-polymorphism-based genomewide linkage analysis, the locus was mapped to chromosome 3p. Haplotype analysis defined the locus to a 13.8-cM interval with a LOD score of 5.04. This is the first description of a monogenic form of cutaneous lupus erythematosus. Identification of the gene responsible for familial chilblain lupus may shed light on the pathogenesis of common forms of connective-tissue disease such as systemic lupus erythematosus.

Gonococcal Arthritis (Disseminated Gonococcal Infection)

Septic arthritis caused by N gonorrhoeae is monoarticular or pauciarticular, and is more commonly associated with positive synovial fluid cultures and negative blood cultures. Gonococcal bacteremia is more likely to be associated with polyarthralgias and skin lesions. The diagnosis of gonococcal arthritis or DGI is also secure if a mucosal gonococcal infection is documented in the presence of a typical clinical syndrome that responds promptly to appropriate antimicrobial therapy. Hospitalization is indicated in patients with suppurative arthritis or when the diagnosis is in doubt. Initial treatment with ceftriaxone or another advanced-generation cephalosporin is warranted until signs and symptoms have improved; continuation of treatment for a total period of therapy of 1 week can be accomplished with a fluoroquinolone.

C5 complement deficiency in a Spanish family. Molecular characterization of the double mutation responsible for the defect

The complement C5 deficiency is a recessive autosomal defect associated with recurrent infectious episodes, generally caused by Gram-negative micro-organisms. To date, only two mutations responsible for C5 deficiency have been characterized, both in heterozygosis. In this paper, we evaluate by immunochemical methods the C5 deficiency in a six-member family, in which one member suffered from meningococcal sepsis and several pneumonia episodes; and a second one with two bacterial meningitis episodes and frequent tonsillitis, pneumonia and herpetic episodes. We also characterize the molecular basis of this deficiency. No C5 protein was found in the serum from three of the children. They were found to be homozygous for a double mutation in the exon 40 of the C5 gene. The parents and the other children have half-normal levels of C5, and they were heterozygotes for the double mutation. This mutation modifies the reading frame, leading to a premature stop codon, and the resulting protein lacks 50 amino acids. As a result, homozygotes and heterozygotes have a total or a partial C5 deficiency respectively. This is the first report of a whole molecular characterization of C5 deficiency.

Host genes and infectious diseases. HIV, other pathogens, and a public health perspective

INTRODUCTION

The global impact of infectious diseases is tremendous. In 1996, the 17 million deaths from infectious diseases accounted for one third of all deaths worldwide, while the acute and chronic morbidity from infectious diseases adds an additional great burden on global health. Multiple factors, host and nonhost, influence the susceptibility of individuals and populations to infectious diseases, as well as the severity of the illness once infected.

METHODS

We review the influence of host genes on the susceptibility to and severity of viral, bacterial, parasitic and fungal infectious diseases, on vaccine responsiveness and on treatments for infections. HIV/AIDS is discussed in detail because it is an example of an infectious disease influenced by multiple host genes and because of its impact. Although the HIV/AIDS pandemic dates only since the late 1970s, it has claimed the lives of 11 million people worldwide and, today, more than 30 million people are estimated to be HIV infected.

CONCLUSION

Our greater understanding of the genetic factors that influence morbidity and mortality of infectious disease leads to new avenues of prevention and treatment that can improve the health of individuals and populations.

Childhood acute bacterial meningitis in the Sudan: an epidemiological, clinical and laboratory study

The aims of the present study were to document the epidemiology, clinical features and complications of childhood acute bacterial meningitis (ABM) in The Sudan during both an inter-epidemic (endemic) period (1985-1986), and the 1988 serogroup A epidemic; and to examine the phenotypic and genetic similarities and differences of Neisseria meningitidis strains isolated in The Sudan and Sweden. A new enzyme immunoassay test (Pharmacia Meningitis EIA-Test) was evaluated as a potential rapid diagnostic method for the detection of Haemophilus influenzae (HI) type b, Neisseria meningitidis (MC) and Streptococcus pneumoniae (PNC). The test was found to have good sensitivity (0.86) and specificity (0.95) in the inter-epidemic period; and to be adaptable to the field work in The Sudan during the 1988 MC epidemic. During inter-epidemic (endemic) situations in The Sudan, greater than 90% of childhood ABM was caused by one of the three organisms, HI type b, MC and PNC. HI accounted for 57% of the cases. The peak incidence (76%) of HI cases was in infants (less than 12 months) similar to the situation in other African countries. The overall case fatality ratio was 18.6%. Prospective follow-up of survivors for 3-4 years revealed that an additional 43% either died or had permanent neurological complications, the most prevalent and persistent of which was sensorineural hearing loss recorded in 22% of long term survivors. Post-meningitic children were found to have significantly lower intelligence quotients (92.3 +/- 13.9) than their sibling controls (100.7 +/- 10.2, P = 0.029). Features of the large serogroup A sulphonamide resistant MC epidemic (February-August 1988) in Khartoum are described. An estimated annual incidence of 1,679/100,000 was recorded at the peak of the epidemic. The highest attack rate was in young children less than 5 years, as in many other African countries; nevertheless, a high morbidity was observed in adults (31% of the cases greater than or equal to 20 years). The clinical features, mortality (6.3%) and short term sequelae in Sudanese children were generally within the framework described for MC disease elsewhere. Detailed analysis of MC isolates from Sudan and Sweden by characterizing their electrophoretic enzyme types, DNA restriction endonuclease pattern and outer membrane proteins, revealed that serogroup A MC clone III-1 was responsible of The Sudan epidemic in 1988 and has been the dominant serogroup A organism in Sweden since 1973. The Sudanese strains isolated prior to the epidemic (1985) were clone IV-1.(ABSTRACT TRUNCATED AT 250 WORDS)

[Hereditary C5 deficiency and recurrent Neisseria meningitidis meningitis]

Deficiencies of the terminal C fragments of the complement system are known to be associated with a remarkable increase in the frequency of Neisseria infections. The correlation is even closer between deficiency of C5 and recurrent N. meningitidis meningitis. The reasons for this bacterial specificity and the immunopathological mechanisms involved have not been clearly established. However, it is known that only adult subjects with homozygous deficiency are affected and that the deficiency is transmitted as an autosomal recessive trait unrelated to the HLA system.

[Recurrent meningitis in familial deficiency of the 8th component of the complement system]

An 18-year-old man suffered from recurrent bacterial meningitis. Investigation of the complement system revealed deficiency of the 8th complement component (C8) in the patient and his sister. Genetic defects of the terminal complement components C5 to C8 predispose to Neisseria infections, probably due to a lack in bacteriolytic activity. It is to be noted that 1 year ago the patient had been hospitalized for a culture-proved pneumococcal meningitis.

Meningococcal disease in congenital absence of the fifth component of complement

We describe a family in which 2 brothers had meningococcal infection, 1 of them twice. Their parents were first degree cousins. The brothers showed a complete, isolated deficiency of C5, both antigenic and functional. The parents had half-normal values, and the data are compatible with an inherited C5 deficiency where the defect is transmitted as an autosomal codominant trait.

The terminal complement complex in sera deficient in the eighth component of complement (C8)

The terminal complement complex (TCC) was quantified in sera from patients with a genetic deficiency of C8 alpha-gamma or C8 beta. The individual sera contained only trace amounts of TCC compared with a normal serum pool. The content of TCC increased after mixing the two sera, which was consistent with reconstitution of C8 activity. Only a moderate increase in TCC was obtained after zymosan activation of the individual sera, whereas activation of the mixture resulted in high amounts of TCC. C8 was demonstrated in the TCC of both deficient sera. These results may indicate that functional C8 is present in trace amounts despite the genetic deficiency, and that the terminal pathway may function to some extent although not enough to be detectable in less sensitive assays.

Membrane attack by complement

Membrane attack by complement involves the self-assembly on membranes of five hydrophilic proteins (C5b, C6, C7, C8 and C9) to an amphiphilic tubular complex comprising approximately 20 subunits. The hydrophilic-amphiphilic transition of the precursor proteins is achieved by restricted unfolding and exposure of previously hidden hydrophobic domains. Restricted unfolding, in turn, is driven by high-affinity protein-protein interactions resulting in the formation of amphilic complexes. Circular polymerization of C9 to a tubular complex (poly C9) constitutes the molecular mechanism for transmembrane channel assembly and formation of ultrastructural membrane lesions.

Fulminant meningococcal infections in a family with inherited deficiency of properdin

Three males in a large kindred died of meningococcal infections. In the index patient, properdin (P) was not detectable in serum. Two healthy males with a selective P deficiency were found in the family. There was no general susceptibility to infections, nor to other diseases as suggested by the family history. The serum bactericidal activity for Neisseria meningitidis group C, isolated from the index patient, was moderately reduced in P deficient serum, and was improved by addition of purified P.

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.

Molecular organization of C9 within the membrane attack complex of complement. Induction of circular C9 polymerization by the C5b-8 assembly

Evidence has been presented suggesting that during assembly of the membrane attack complex (MAC) of complement, the C5b-8 complex induces polymerization of C9. The C9 polymer was detected by sodium dodecyl sulfate (SDS) gel electrophoresis of MAC isolated from complement-lysed erythrocytes. It resembled the previously described polymerized C9 (poly C9) produced from isolated monomeric C9 by prolonged incubation at 37 degrees C in that it was resistant to dissociation by SDS and reducing agents and had an apparent molecular weight of approximately 1.1 million. The presence of poly C9 in the MAC was further supported by the expression of identical neoantigens by the MAC and poly C9 and by the high C9 content of the MAC relative to its other constituents. Isolated C8 in solution was found to have a single C9-binding site. In mixture, the two proteins formed a reversible equimolar complex that had a sedimentation coefficient of 10.5S. In contrast, a single, cell-bound C5b-8 complex was found to bind up to 12-15 C9 molecules and clusters of C5b- 8 bound 6-8 C9 molecules per C8 molecule. In either case, typical ultrastructural membrane lesions were observed, suggesting that the membrane lesion is identical with the tubular poly C9 consisting of 12-16 C9 molecules, and that the MAC can have either the composition (C5b-8)polyC9 or (CSb-8)(2)polyC9. When C9 input was restricted so that the molar C9/C8 ratio was less than or equal to 3, C9-induced aggregates of C5b-8 were observed but virtually no circular membrane lesions were found. We suggest, therefore, that C9, at low dosage, causes cross-linking of multiple C5b-8 complexes within the target membrane and that, at high dosage, C9 is polymerized by C5b-8 to form a transmembrane channel within the MAC assembly. It is primarily the C9 polymer that evokes the ultrastructural image of the MAC or of membrane lesions caused by complement.

Genetic control of susceptibility to Cryptococcus neoformans in mice

Inbred mice injected intravenously with 5 x 10(6) cells of Cryptococcus neoformans showed two patterns of survival: sensitive (A/WySn, A.BY, A/J, DBA/2J, NZB/B1NJ, and SWR/J) and resistant [C57BL/10Sn, B10.A, B10.A (2R), B10.S (7R),C57BR/cdJ, C58/J, C3H/HeJ, BALB/c, DBA/1J, and SJL/J]. Relative susceptibility based on survival time was shown to correspond to differences obtained for 50% lethal dose values. Either decreasing the dose of organisms or changing to the intraperitoneal route of inoculation resulted in prolonged survival times, but neither change affected the observed patterns of survival. F1 hybrids between different sensitive strains were also sensitive, whereas F1 hybrids between sensitive and resistant strains were resistant, indicating a dominant mode of inheritance. Sensitivity and resistance were shown to be under single gene control by segregation analysis in F2 progeny produced by inbreeding (B10.A x A/WySn)F1 hybrids and in (F1 x A/WySn) backcross progeny. Blood obtained from parental strains, F1, F2, and backcross hybrids was tested for the presence or absence of hemolytic complement. Mice lacking hemolytic complement activity in their sera are homozygous for the Hc(0) allele at the Hc locus on chromosome 2 and are deficient in the complement component C5. A 1:1 correspondence was found between C5 deficiency and sensitivity to C. neoformans. Resistance was shown to cosegregate with the presence of hemolytic complement in the F2 and the backcross progenies.

Fulminant meningococcemia in a child with hereditary deficiency of the seventh component of complement and proteinuria

A previously healthy 14-year-old boy presented with fulminant meningococcemia. He was found to have a total deficiency of C7. His serum totally lacked bactericidal activity against Neisseria meningitidis. Addition of purified C7 restored the serum hemolytic and bactericidal activity. Susceptibility to disseminated Neisseria infections has previously been reported in 3 patients with C7 deficiency, as well as in a few patients with deficiency of C5, C6 and C8. These findings emphasize the importance of intact complement mediated bactericidal activity in host defense against disseminated Neisseria infections. Evaluation of the complement system in individuals with Neisseria infections appears mandatory.