Hereditary Deficiency of the Second Component of Complement: Early Diagnosis and 21-Year Follow-Up of a Family.

Complement deficiencies are rare and often underdiagnosed primary immunodeficiencies that may be associated with invasive bacterial diseases. Serious infections with encapsulated organisms (mainly Streptococcus pneumoniae, but also Neisseria meningitides and Haemophilus influenzae type B) are frequent in patients with a deficiency of the second component of complement (C2), but no data are available on long-term follow-up. This study aimed to evaluate the long-term clinical outcome and the importance of an early diagnosis and subsequent infection prophylaxis in C2 deficiency. Here, we report the 21-year follow-up of a whole family which was tested for complement parameters, genetic analysis and biochemical measurements, due to recurrent pneumococcal meningitis in the elder brother. The two sons were diagnosed with homozygous type 1 C2 deficiency, while their parents were heterozygous with normal complement parameters. For the two brothers, a recommended vaccination program and antibiotic prophylaxis were prescribed. During the long-term follow-up, no severe/invasive infections were observed in either patient. At the age of 16, the younger brother developed progressive hypogammaglobulinemia of all three classes, IgA, IgM and IgG. A next generation sequencing panel excluded the presence of gene defects related to primary antibody deficiencies. Our data show that early diagnosis, use of vaccinations and antibiotic prophylaxis may allow a normal life in hereditary C2 deficiency, which can be characterized using functional and genetic methods. Moreover, a periodical check of immunoglobulin serum levels could be useful to detect a possible hypogammaglobulinemia.

Urticarial vasculitis in the childhood with C2 hypocomplementenemia: a rare case.

We report a first case of hypocomplementemic urticarial vasculitis of C2 fraction in a child, with cutaneous manifestation only, with no reports in scientific literature.

Post-vaccine glomerulonephritis in an infant with hereditary C2 complement deficiency: case study.

We describe a case of a post vaccine immune complex-mediated glomerulonephritis in an infant with compound heterozygous mutations of C2 complement component gene, which is the first such case in the literature. The three and a half months old boy presented with clinical and laboratory signs of nephritic syndrome and was successfully treated with methylprednisolone. An explanation of such a clinical picture may lie in the interaction between C2 deficiency and vaccination.

Vaccination against encapsulated bacteria in hereditary C2 deficiency results in antibody response and opsonization due to antibody-dependent complement activation.

Hereditary C2 deficiency (C2D) is an important susceptibility factor for invasive infections caused by encapsulated bacteria such as pneumococci and Haemophilus influenzae type b. The infections are mostly seen in childhood indicating that antibody-mediated acquired immunity is affected. C2D persons and healthy controls were vaccinated with ActHIB® and Pneumo23®. Analysis of specific antibodies to pneumococci serotype 6B, 7F, and 23F, and Hib was performed. Post-vaccination IgG antibodies against pneumococci serotype 6B and 23F at a concentration ≥1.0mg/L was found in similar frequency in C2D persons and controls. Post-vaccination sera from C2D persons showed poor complement-mediated opsonization and phagocytosis of pneumococci by granulocytes when depending on classical and lectin pathway activation only, but increased (p=0.007) and equaled that of the normal controls when also alternative pathway activation was allowed due to antibody-dependent C2 bypass activation. In conclusion, the C2D persons benefited from the vaccination and achieve an increased phagocytic capacity.

Recurrent septic shock in a 34-year-old woman.

A 34-year-old woman presented to the Emergency Room (ER) with an acute presentation of septic shock that required fluid and pressor support in the Intensive Care Unit. History revealed this was her third episode of such a presentation with asymptomatic periods in between. She responded well to medical interventions but reported persistent joint pain. Immunologic workup revealed her diagnosis.

Human genetic deficiencies reveal the roles of complement in the inflammatory network: lessons from nature.

Complement component C5 is crucial for experimental animal inflammatory tissue damage; however, its involvement in human inflammation is incompletely understood. The responses to gram-negative bacteria were here studied taking advantage of human genetic complement-deficiencies--nature's own knockouts--including a previously undescribed C5 defect. Such deficiencies provide a unique tool for investigating the biological role of proteins. The experimental conditions allowed cross-talk between the different inflammatory pathways using a whole blood model based on the anticoagulant lepirudin, which does not interfere with the complement system. Expression of tissue factor, cell adhesion molecules, and oxidative burst depended highly on C5, mediated through the activation product C5a, whereas granulocyte enzyme release relied mainly on C3 and was C5a-independent. Release of cytokines and chemokines was mediated to varying degrees by complement and CD14; for example, interleukin (IL)-1beta and IL-8 were more dependent on complement than IFN-gamma and IL-6, which were highly dependent on CD14. IL-1 receptor antagonist (IL-1ra) and IFN-gamma inducible protein 10 (IP-10) were fully dependent on CD14 and inversely regulated by complement, that is, complement deficiency and complement inhibition enhanced their release. Granulocyte responses were mainly complement-dependent, whereas monocyte responses were more dependent on CD14. Notably, all responses were abolished by combined neutralization of complement and CD14. The present study provides important insight into the comprehensive role of complement in human inflammatory responses to gram-negative bacteria.

Essential role of factor B of the alternative complement pathway in complement activation and opsonophagocytosis during acute pneumococcal otitis media in mice.

We recently reported that the complement system plays a pivotal role in innate immune defense against Streptococcus pneumoniae during acute otitis media (OM) in mice. The current study was designed to determine which of the complement pathways are activated during acute pneumococcal OM and whether components of complement are expressed in the middle ear epithelium. Gene expression was determined by quantitative PCR, enzyme-linked immunosorbent assay (ELISA), and immunofluorescence staining. We found that S. pneumoniae induced increased gene expression of factor B of the alternative complement pathway and C3 in mouse middle ear epithelium. Activation of factor B and C3 in the middle ear lavage fluids was significantly greater than in simultaneously obtained serum samples as determined by Western blotting. Using mice deficient in complement C1qa, factor B, and factor B/C2, we found that complement C3 activation and opsonophagocytosis of S. pneumoniae were greatly attenuated in factor B- and factor B/C2-deficient mice. These findings support the concept that local complement activation is an important host innate immune response and that activation of the alternative complement pathway represents one of the innate immune defense mechanisms against pneumococcal infection during the early stage of acute OM.

Complement and antibody primary immunodeficiency in juvenile systemic lupus erythematosus patients.

OBJECTIVE: To evaluate the frequency of primary immunodeficiencies (PID) in juvenile systemic lupus erythematosus (JSLE) patients. METHODS: Some 72 JSLE patients were analyzed for levels of immunoglobulin classes and IgG subclasses and early components of the classical complement pathway. Determination of C4 gene copy number (GCN) and detection of type I C2 deficiency (D) were also performed. RESULTS: PID was identified in 16 patients (22%): C2D in three, C4D in three, C1qD in two, IgG2D (<20 mg/dl) in four, IgAD (<7 mg/dl) in three, and IgMD (<35 mg/dl) in three; one of these patients presented IgA, C2 and C4D. Two patients had low C4 GCN and two had type I C2D. Demographic data, family history of autoimmune disease and PID, JSLE clinical findings, occurrence of infections, disease activity and therapies were similar in patients with and without PID (p > 0.05). Remarkably, the median of Systemic Lupus International Collaborating Clinics/ACR-damage index (SLICC/ACR-DI) was significantly higher in JSLE patients with PID compared with patients without these abnormalities (p = 0.0033), likewise the high frequency of SLICC/ACR-DI > 1 (p = 0.023). CONCLUSIONS: A high frequency of PID was observed in JSLE patients, suggesting that these defects may contribute to lupus development. Our findings indicate that these two groups of PID should be investigated in severe pediatric lupus.

Increased serum bactericidal activity of autologous serum in C2 deficiency after vaccination against Haemophilus influenzae type b, and further support for an MBL-dependent C2 bypass mechanism.

Deficiencies of C2 and other components of the classical pathway of complement are associated with increased risk of infections with encapsulated bacteria, such as Haemophilus (H.) influenzae. Defense against H. influenzae is dependent on specific antibodies and complement, which mediate serum bactericidal activity (SBA) and opsonization. Due to lack of normal classical and lectin complement pathway function in C2 deficiency (C2D), SBA would have to depend either on the alternative pathway or on C2 bypass mechanisms. Here we studied SBA against H. influenzae type b (Hib) before and after vaccination in a group of C2-deficient persons, as the bactericidal capacity of antibodies in autologous complement in relation to vaccination has not been investigated at group level in C2D. Sera from 22 persons with C2D and 26 healthy controls were available. Out of these, 18 persons with C2D and all controls had been vaccinated with Act-HIB®. SBA against Hib bacteria was analyzed with autologous serum as the only complement source. Antibodies to Hib capsular polysaccharide had been analyzed previously. Concentrations of mannose-binding lectin (MBL) and other complement components were measured in serum. SBA of both C2-deficient persons and controls was significantly more efficient after vaccination (p = 0.002 and p < 0.0001, respectively). After vaccination, all but two C2-deficient sera and one control serum showed sufficient SBA (<50% surviving bacteria). Before vaccination, SBA of C2-deficient sera was negatively correlated to serum concentrations of MBL (lower proportion of surviving bacteria with higher MBL concentration; r = -0.55, p = 0.008). After vaccination, SBA of C2-deficient sera was negatively correlated to serum concentrations of IgG Hib antibodies (r = -0.56, p = 0.01). In conclusion, SBA against Hib in autologous serum is increased after vaccination in persons with C2D. In unvaccinated C2-deficient persons SBA was correlated to MBL concentration, providing further support for an MBL-dependent C2 bypass mechanism operating in C2D.

Critical roles of complement and antibodies in host defense mechanisms against Neisseria meningitidis as revealed by human complement genetic deficiencies.

Certain complement defects are associated with an increased propensity to contract Neisseria meningitidis infections. We performed detailed analyses of complement-mediated defense mechanisms against N. meningitidis 44/76 with whole blood and serum from two adult patients who were completely C2 or C5 deficient. The C5-deficient patient and the matched control were also deficient in mannose-binding lectin (MBL). The proliferation of meningococci incubated in freshly drawn whole blood was estimated by CFU and quantitative DNA real-time PCR. The serum bactericidal activity and opsonophagocytic activity by granulocytes were investigated, including heat-inactivated postvaccination sera, to examine the influence of antimeningococcal antibodies. The meningococci proliferated equally in C2- and C5-deficient blood, with a 2 log(10) increase of CFU and 4- to 5-log(10) increase in DNA copies. Proliferation was modestly decreased in reconstituted C2-deficient and control blood. After reconstitution of C5-deficient blood, all meningococci were killed, which is consistent with high antibody titers being present. The opsonophagocytic activity was strictly C2 dependent, appeared with normal serum, and increased with postvaccination serum. Serum bactericidal activity was strictly dependent on C2, C5, and high antibody titers. MBL did not influence any of the parameters observed. Complement-mediated defense against meningococci was thus dependent on the classical pathway. Some opsonophagocytic activity occurred despite low levels of antimeningococcal antibodies but was more efficient with immune sera. Serum bactericidal activity was dependent on C2, C5, and immune sera. MBL did not influence any of the parameters observed.

Enhanced susceptibility to acute pneumococcal otitis media in mice deficient in complement C1qa, factor B, and factor B/C2.

To define the roles of specific complement activation pathways in host defense against Streptococcus pneumoniae in acute otitis media (AOM), we investigated the susceptibility to AOM in mice deficient in complement factor B and C2 (Bf/C2(-/)(-)), C1qa (C1qa(-/)(-)), and factor B (Bf(-)(/)(-)). Bacterial titers of both S. pneumoniae serotype 6A and 14 in the middle ear lavage fluid samples from Bf/C2(-/)(-), Bf(-)(/)(-), and C1qa(-/)(-) mice were significantly higher than in samples from wild-type mice 24 h after transtympanical infection (P < 0.05) and remained persistently higher in samples from Bf/C2(-/)(-) mice than in samples from wild-type mice. Bacteremia occurred in Bf/C2(-/)(-), Bf(-)(/)(-), and C1qa(-/)(-) mice infected with both strains, but not in wild-type mice. Recruitment of inflammatory cells was paralleled by enhanced production of inflammatory mediators in the middle ear lavage samples from Bf/C2(-/)(-) mice. C3b deposition on both strains was greatest for sera obtained from wild-type mice, followed by C1qa(-)(/)(-) and Bf(-)(/)(-) mice, and least for Bf/C2(-)(/)(-) mice. Opsonophagocytosis and whole-blood killing capacity of both strains were significantly decreased in the presence of sera or whole blood from complement-deficient mice compared to wild-type mice. These findings indicate that both the classical and alternative complement pathways are critical for middle ear immune defense against S. pneumoniae. The reduced capacity of complement-mediated opsonization and phagocytosis in the complement-deficient mice appears to be responsible for the impaired clearance of S. pneumoniae from the middle ear and dissemination to the bloodstream during AOM.

Hereditary C2 deficiency: Genetic studies and association with the HL-A system.

Herediatary C2-deficiency has been shown to be transmitted asn an autosomal recessive characteristic. Recent evidence indicates that some genetic factors involved in the control of the complement (C) system in both man and mice are governed by genes localized within the major histocompatibility regionmthis study describes a large pedigree of the paternal family of a C2-deficient patient with systemic lupus erythematosusl It is shown that this condition is transmitted as an autosomal recessive trait, the heterozygous carriers having approximately half normal levels of C2. Furthermore, this trait was shown to be inherited in close linkage with an infrequent HL-A typw, 2,4A2. The maternal, C2-defective chromosome was shown to be transmitted by HL-AW10, W18 haplotypemthis same haplotype was described in a similar study by Fu et al. (6) to be associated with C2 deficiencymfinally, a third haplotype HL-A2,W18 carrying a defective C2 gene was demonstrated in a part of this pedigree.

Association of low C2 and C4 serum levels with the HLA-DW2 allele in healthy individuals.

HLA typed unrelated healthy individuals (HLA-DW2 positive n = 64, and HLA-DW2 negative n = 72) were investigated for their C2 functional activity and C4 serum protein levels. For the C2 and C4 levels a bimodal distribution was found in HLA-DW2 positive and HLA-DW2 negative individuals. HLA-DW2 positive persons had a significantly higher incidence of low C2 and C4 serum levels. Our data support the concept that genes governing C2 as well as C4 serum levels are in linkage disequilibrium with the HLA-DW2 allele of the major histocompatibility complex.

Mixed lymphocyte culture determinants and C2 deficiency: LD-7a associated with C2 deficiency in four families.

Four families with C2 deficiency were studied. Among eight HL-A haplotypes involved with C2 deficiency, five were HL-A 10,W18. Three homozygotes for C2 deficiency from different families were mutually nonreactive in mixed lymphocyte cultures (MLC) and the heterozygotes from the fourth family failed to react to the homozygous cells. It appeared that identical MLC determinants were associated with all the genes from the different families that related to C2 deficiency. Further experiments identified the MLC determinant, LD-7a, as being involved. These results suggest marked linkage disequilibrium between the genes for C2 deficiency and the major histocompatibility complex (MHC). Studies of possible recombinants have offered tentative evidence for the positioning of the locus for C2 deficiency with respect to other segments of the MHC.

Activation of the classical pathway of complement by Hageman factor fragment.

A fragment of activated Hageman factor (HFf) has been demonstrated to activate the classical pathway of complement in a manner that is analogous to complement activation by antigen-antibody complexes or aggregated IgG. Thus C1, C4, C2, C3, and C5 were found to be depleted on addition of HFf to serum. The reduction of serum hemolytic activity was maximal upon addition of 5 micrograms HFf and an incubation time of 60 min at 37 degrees C. Consumption of the total complement activity and of the individual components proceeded in a dose-dependent fashion. No comparable activity was observed when equimolar concentrations of either the native Hageman factor (HF) or two-chain activated form of Hageman factor (HFa) were incubated with serum. Further, the ability of HFf to convert serum C3 and C4 was similar to that of aggregated IgG as assessed by immunoelectrophoresis. This function of HFf appeared to be independent of plasminogen (or plasmin) since plasminogen-free serum was indistinguishable from normal serum. Radial double immunodiffusion experiments using antiserum to C1q, C1r, and C1s on HFf-treated serum demonstrated the dissociation of the C1 trimolecular complex, with concomitant reduction of C1r antigenicity that is indicative of C1 activation. Thus, HFf appears to lead to C1 activation upon incubation with serum or when incubated with partially purified C1. This may represent a control link between activation of the intrinsic coagulation-kinin pathway and the initiation of the classical complement cascade.

Complete complement deficiency in a large cohort of familial systemic lupus erythematosus.

Genetic complete deficiency of the early complement components such as C1, C2 and C4 commonly results in a monogenetic form of systemic lupus erythematosus (SLE). However, previous studies have examined groups of complete complement deficient subjects for SLE, while a familial SLE cohort has not been studied for deficiencies of complement. Thus, we undertook the present study to determine the frequency of hereditary complete complement deficiencies among families with two or more SLE patients. All SLE patients from 544 such families had CH50 determined. Medical records were examined for past CH50 values. There were 66 individuals in whom all available CH50 values were zero. All but four of these had a SLE-affected relative with a non-zero CH50; thus, these families did not have monogenetic complement deficient related SLE. The four remaining SLE-affected subjects were in fact two sets of siblings in which three of the four SLE patients had onset of disease at <18 years of age. Both patients in one of these families had been determined to have C4 deficiency, while the other family had no clinical diagnosis of complement deficiency. In this second family, one of the SLE patients had had normal C4 and C3 values, indicating that either C1q or C2 deficiency was possible. Thus, only 2 of 544 SLE families had definite or possible complement deficiency; however, 1 of 7 families in which all SLE patients had pediatric onset and 2 of 85 families with at least 1 pediatric-onset SLE patent had complete complement deficiency. SLE is found commonly among families with hereditary complement deficiency but the reverse is not true. Complete complement deficiency is rare among families with two or more SLE patients, but is concentrated among families with onset of SLE prior to age 18.

Recurrent macroscopic hematuria in a pediatric patient: is it early to diagnose as having type I hereditary C2 deficiency?

Hereditary C2 deficiency is the most common early complement deficiency and characterized by recurrent infections and autoimmunity despite most patients are also asymptomatic. Type I hereditary C2 deficiency is caused by a heterozygous deletion in C2 gene resulting in early stop codon and lack of C2 production. Clinical spectrum may vary and pure nephrological involvement without the presence of recurrent infections is scarce in hereditary C2 deficiency.We report here a previously healthy 14-year-old boy presenting recurrent self-limited macroscopic hematuria and persistently low serum C4 levels, diagnosed as having type I hereditary C2 deficiency with confirming a novel heterozygote deletion (c.1567 + 22_1567 + 43del) in C2 gene. He has been remained asymptomatic for the next 18 months. Since the diagnosis of C2 deficiency was made in the absence of organ-threatening involvement such as immune complex-mediated glomerulonephritis, we think that early diagnosis and optimal follow-up may improve life-span of the patients with hereditary early complement deficiencies.

Complement classical pathway components are all important in clearance of apoptotic and secondary necrotic cells.

Inherited deficiencies in components of the classical complement pathway are strong disease susceptibility factors for the development of systemic lupus erythematosus (SLE) and there is a hierarchy among deficiency states, the strongest association being with C1q deficiency. We investigated the relative importance of the different complement pathways regarding clearance of apoptotic cells. Phagocytosis of labelled apoptotic Jurkat cells by monocyte-derived macrophages in the presence of sera from individuals with complement deficiencies was studied, as well as C3 deposition on apoptotic cells using flow cytometry. Sera from individuals deficient in C1q, C4, C2 or C3 all showed decreased phagocytosis. Mannose binding lectin (MBL) and the alternative pathway did not influence phagocytosis. Notably, the components of the complement classical pathway, including C1q, were equally important in clearance of apoptotic cells. This indicates that deposition of C3 fragments is of major significance; we therefore studied C3 deposition on apoptotic cells. Experiments with MBL-deficient serum depleted of C1q or factor D confirmed the predominance of the classical pathway. At low dilution, sera deficient of C1q, C4 or C2 supported C3 fragment deposition demonstrating alternative pathway activation. In conclusion, we have found that complement-mediated opsonization and phagocytosis of apoptotic cells, particularly those undergoing secondary necrosis, are dependent mainly upon an intact classical pathway. The alternative pathway is less important, but may play a role in some conditions. C1q was not more important than other classical pathway components, suggesting a role in additional pathogenetic processes in SLE other than clearance of apoptotic cells.

Genetic linkage between the HL-A system and a deficit of the second component (C2) of complement.

From a family of 14 individuals, evidence was obtained suggesting linkage between the HL-A haplotypes and the transmission of a 50 percent deficit in the functional activity of the C2 component of complement.

Gonococcal Arthritis and C2 Deficiency. / Artritis gonocócica y déficit de C2.

Disseminated gonococcal infection is a rare presentation of the sexually transmitted pathogen, Neisseria gonorrhoeae. Here, we report the case of a 64-year-old woman with disseminated gonococcal infection, which started with symptoms of oligoarthritis and malaise. Neisseria gonorrhoeae was identified in the carpal synovial fluid. The follow-up study revealed an absence of total hemolytic complement and complement C2 was not detected. Being relatively common, C2 deficiency has been associated with disseminated gonococcal infection in a few cases. We present a new case and discuss those previously published.