Inherited deficiencies of complement in rheumatic diseases

Novel insights on the role of the innate immune system in systemic sclerosis

Over the last several years the involvement of the innate immune system in the pathogenesis of autoimmune diseases such as systemic lupus erythematosus (SLE) has become well established. As systemic sclerosis (SSc; scleroderma) shares clinical features and autoantibodies with SLE, investigation has recently focused on the role of innate immunity in SSc. This has been supported by recent genetic studies. However, unlike SLE and other related autoimmune diseases, SSc patients suffer from pathologic fibrosis of skin and internal organs. The fibrotic component of SSc shares several features with syndromes following environmental exposures to agents such as organic solvents, silica dust and bleomycin. Recent work in SSc and these related fibrotic diseases have identified several areas in which innate immunity can stimulate inflammation as well as fibrosis. This article will focus on the recent discoveries identifying a prominent role of cells of the innate immune system, pattern recognition receptors, and activation of dendritic cells in the pathogenesis of SSc.

Complement deficiency and systemic lupus erythematosus: consensus and dilemma

The involvement of the complement system in the pathogenesis of autoimmune diseases is a matter of debate. However, the link between complement abnormalities and systemic lupus erythematosus (SLE) is well established and widely described. Homozygous and/or heterozygous complement-component deficiencies of the classical pathway (C1q, C1r, C1s, C4A, C4B and C2) are causally associated with susceptibility to the development of SLE. Although the severity of the disease and the strength of the association are heterogeneous for deficiencies of these proteins, they commonly cause peculiar SLE syndromes with an early age of onset, a susceptibility to bacterial infections and negative anti-dsDNA antibodies. In this review, we highlight the available data on complement deficiency and SLE with a focus on deficiencies in classical complement pathway components. We also discuss the paradox of the link between complement deficiency and lupus. The complement system acts as a 'friend' through the clearance of immune complexes and apoptotic cells, which explains the close association between complement deficiency and lupus. It also acts as an 'enemy' by participating in the effector inflammatory phase of the autoimmune response. Understanding the importance of complement deficiencies should provide novel targets for therapeutic interventions in the modulation of the immune response.

Laboratory tests in the diagnosis and follow-up of pediatric rheumatic diseases: an update

OBJECTIVES

We reviewed the literature to evaluate the role of common laboratory tests and to examine the recent progress in the laboratory diagnosis of pediatric rheumatic diseases.

METHODS

We used the PubMed database (1950-2008) to search for the keywords "laboratory," "erythrocyte sedimentation rate" (ESR), "C-reactive protein" (CRP), "blood cytology," "procalcitonin" (PCT), "complement system," "ferritin," "antistreptolysin O titer" (ASO), "autoantibodies," "genetic studies," in conjunction with "rheumatic disease in children" and "pediatric autoimmune diseases." All relevant original and review articles in English were reviewed as well as textbooks of pediatric rheumatology.

RESULTS

Laboratory tests (ESR, CRP, blood cytology, complement system, ferritin, ASO titer) play an important role in confirming a diagnosis and in the follow-up of rheumatic diseases in the pediatric age group. The ESR is probably the most widely measured index of the acute phase response. Measurement of CRP is very useful in the rapid diagnosis of infection as a progressive increase can be shown in the first 48 hours. Also, the subsequent fall in serum CRP concentration on resolution of inflammation is useful for monitoring the efficacy of treatment. In chronic diseases, a combination of CRP and ESR may provide the most useful information. Cytopenia and different forms of anemia can be encountered in many rheumatic diseases: they can be related to disease activity or to therapeutic side effects. Determination of complement levels (C3 and/or C4) is useful in the follow-up of systemic lupus erythematosus (SLE) and membranoproliferative glomerulonephritis. Ferritin is a laboratory hallmark of primary and secondary hemophagocytic lymphohistiocytosis. ASO titer should be obtained to confirm a diagnosis of acute rheumatic fever; other important antibody markers of streptococcal infection include antihyaluronidase, antideoxyribonuclease B, and antistreptokinase antibodies. We also found that, in the pediatric age, the main indication for synovial fluid analysis is suspected joint infection. Antinuclear antibodies, anti-Smith antigen, and anti-double-stranded DNA antibodies are important in the diagnosis of SLE, are useful prognostic markers, and facilitate clinical and treatment follow-up. Anti-SSA/Ro and anti-SSB/La antibodies are associated with Sjögren's syndrome and congenital heart block, while the anti-U1 small nuclear ribonucleoprotein antibodies show high specificity for mixed connective tissue disease. Repetitive spontaneous abortions, thrombocytopenia, and many types of venous or arterial thrombosis are associated with antiphospholipid antibodies. The presence of cytoplasmic antineutrophil antibodies is essential in the diagnosis of Wegener granulomatosis. The discovery of underlying single causative gene defects led to the identification of several autoinflammatory diseases, a group of genetic disorders characterized by recurrent attacks of inflammation (hereditary periodic fever syndromes). These include familial Mediterranean fever due to mutations in the Mediterranean fever (MEFV) gene, hyperimmunoglobulinemia D syndrome due to mutations in the MK gene for mevalonate kinase, cryopyrinopathies such as Muckle-Wells syndrome or neonatal-onset multisystemic inflammatory disease (neonatal-onset multisystemic inflammatory disease or chronic infantile neurological cutaneous and articular (CINCA)) associated with cold-induced autoinflammatory syndrome 1 gene mutations, and tumor necrosis factor receptor-associated periodic syndrome due to mutation of TNF receptor I gene.

CONCLUSIONS

Laboratory investigations play an important role in the diagnosis and follow-up of inflammatory rheumatic diseases in children. A good history and a complete physical examination are the best screening tests. Routine laboratory tests are useful to confirm a suspected diagnosis, to assess disease activity, and to measure the response and toxicity to treatment. Only a few tests represent diagnostic criteria such as antinuclear antibodies and anti-double-stranded DNA in SLE or cytoplasmic antineutrophil cytoplasmic autoantibodies in Wegener's granulomatosis. Recent advances in molecular genetics have impacted diagnosis, pathogenesis, and treatment in genetic fever syndromes.

Differential expression in lupus-associated IL-10 promoter single-nucleotide polymorphisms is mediated by poly(ADP-ribose) polymerase-1

Systemic lupus erythematosus (SLE) is a complex, multifactorial autoimmune disease characterized by the dysregulation of T and B cells that leads to hyperactivity of B cells and production of autoantibodies, and involves both environmental and genetic factors. Interleukin-10 (IL-10) is a candidate susceptibility gene in SLE. In particular, three IL-10 promoter single-nucleotide polymorphisms (SNPs; -1082A/G, -819T/C and -592A/C) are strongly associated with the pathogenesis of SLE. We found that the homozygous GCC haplotype linked to greater SLE severity confers higher IL-10 gene transcriptional activity than the ATA haplotype in macrophages that encounter apoptotic cells, because of the differential DNA binding to the -592 SNP by a nuclear protein uniquely induced by apoptotic cells. We identified this protein as poly(ADP-ribose) polymerase-1, confirmed its physiological role and characterized its molecular properties in modulating IL-10 production during phagocytosis of apoptotic cells. This study unveils a novel direct link between DNA damage repair/apoptosis pathways and IL-10-mediated immune regulation.

Hereditary Complement Deficiency and Lupus: Report of Four Tunisian Cases

The aim of the study was to assess the clinical and immunological profile of lupus erythematosus (LE) patients with inherited complement deficiency (ICD). A laboratory-based study was conducted in which all LE patients with hypocomplementemia were included. ICD was assessed by hemolytic and antigenic assays. Type I C2 deficiency was assessed by polymerase chain reaction (PCR). ICD was diagnosed in four cases. In three systemic LE patients, ICD were: homozygous C2 deficiency in the first case, heterozygous C2 deficiency in the second, and homozygous C1q deficiency in the third case. In a discoid LE patient, a combined homozygous C2 and C6 deficiency was diagnosed. Almost all of our patients presented the classical clinical and immunological features of LE associated with ICD. Severe lupus with renal involvement and recurrent infections was present in half of the patients suggesting that these patients are prone to a serious management.

The combination of complement deficiency and cigarette smoking as risk factor for cutaneous lupus erythematosus in men; a focus on combined C2/C4 deficiency

BACKGROUND

Although deficiencies in the early components of the complement system were among the first identified genetic risk factors for systemic lupus erythematosus (SLE), only a few studies addressed their significance in patients with cutaneous LE (CLE). Among environmental factors, it was postulated that cigarette smoking might intervene in the pathogenesis of LE.

OBJECTIVES

To describe the clinical and biological features of patients with CLE and a complement deficiency. A secondary objective was to assess cigarette smoking in patients with CLE.

PATIENTS AND METHODS

A retrospective study including all patients diagnosed as having LE between 1995 and 2003 in the Dermatology Department of Strasbourg University Hospital. Patient charts were reviewed and those patients in whom a C4 and/or C2 deficiency was diagnosed were included. Two patients with a combined C2/C4 deficiency were analysed in detail.

RESULTS

There were 48 females and 37 males (F/M ratio = 1.3), with a mean age of 41 years at diagnosis; 73% of the patients had chronic LE and 27% subacute CLE. Among 32 screened patients, 24 patients with a mean age of 36 years had a complement deficiency; 17 had a C4A deficiency, five a C4B deficiency and two a combined C4A/C2 deficiency. A high proportion (58%) of these patients was male; 82% of the patients were smokers. This was especially true in males: 94% were smokers compared with 69% of females.

CONCLUSIONS

Partial deficiency of C4, C2 or C4 and C2 is a common finding in patients with CLE. Most male patients with CLE are smokers. It is thus suggested that the combination of cigarette smoking and complement deficiency could be a risk factor for LE in men.

A study of the genetic basis of C4A protein deficiency. Detection of C4A gene deletion by long-range PCR and its associated haplotypes

OBJECTIVE

To study the frequency of a C4A gene deletions as the genetic basis of C4A protein deficiency (C4AQ0) and its associated haplotypes in Icelandic families with systemic lupus erythematosus (SLE).

METHODS

Nine multiplex SLE families were genotyped for C4A gene deletions using a long-range polymerase chain reaction (LR-PCR) method, and major histocompatibility complex (MHC) haplotypes were defined.

RESULTS

Of the SLE patients, first-degree and second-degree relatives, 53.8%, 47.9%, and 28.6% had C4AQ0, respectively. A C4A gene deletion was found to be the genetic basis for C4AQ0 in 64.3% of SLE patients, 60.0% of first-degree and 50.0% of second-degree relatives. All individuals carrying haplotype B8-C4AQ0-C4B1-DR3 had a deletion, and the deletion was also found on haplotypes B8-C4AQ0-C4B1-DR7 and B7-C4AQ0-C4B1-DR3.

CONCLUSION

The study shows that a C4A gene deletion is the most common genetic basis for C4AQ0. It accounts for two-thirds of C4AQ0 and is found on different MHC haplotypes. One-third of C4AQ0 is due to other as yet undefined genetic changes. The results demonstrate a heterogeneous genetic background for C4AQ0, giving further support for the hypothesis that C4AQ0 may be an independent risk factor for SLE.

New advances in measurement of complement activation: lessons of systemic lupus erythematosus

Activation of the complement system plays a fundamental role in the pathogenesis of systemic lupus erythematosus (SLE). For the past several decades, quantifying this process has focused primarily on determination of serum C3 and C4, although the utility of these assays for diagnosis and monitoring disease activity is still debated. During this same timespan, knowledge of the complement system has exploded, with identification of more than 30 proteins, an abundance of newly recognized functions, and even a third pathway of activation. These advances suggest that it is appropriate to revisit the complement system as a potential source of biomarkers for SLE. This paper reviews briefly the role of complement in SLE and other inflammatory diseases, discusses conventional methods for complement measurement and their drawbacks, and focuses on recent advancements in harnessing the complement system for monitoring SLE. Specifically, novel assays that measure cell-bound complement activation products are introduced and their utility as biomarkers of SLE disease activity is discussed.

Association of interleukin-10 promoter polymorphisms with systemic lupus erythematosus

Several lines of evidence suggest interleukin-10 gene (IL-10) is a candidate gene in susceptibility to systemic lupus erythematosus (SLE). We investigated the association of IL-10 promoter single-nucleotide polymorphisms (SNPs) (-3575T/A, -2849G/A, -2763C/A, -1082A/G, -819T/C and -592A/C) and microsatellites (IL10.R, IL10.G) with SLE in 554 Hong Kong Chinese patients and 708 ethnically matched controls. Six haplotypes (hts) were identified from the SNPs. The genotype distribution of the ht1 (T-C-A-T-A), which is associated with low IL-10 production, was different in patients and controls (P=0.009). The homozygous genotype of non-ht1 was significantly increased in patients (P=0.009, odds ratio (OR)=1.80, 95% CI: 1.15-2.82). The frequency of IL10.G4 of IL10.G was also significantly increased in patients (P=0.017, OR=2.53, 95% CI: 1.18-5.40). We found that the homozygous non-ht1 combined with short allele (CA repeat number < or =21) of IL10.G has a dose-dependent effect on SLE susceptibility: non-ht1/non-ht1 with homozygous short allele showed a higher OR (OR=4.11, 95% CI: 1.27-13.2, P=0.018) of association with SLE than the genotype of non-ht1/non-ht1 with heterozygous short/long allele (OR=2.98, 95% CI: 1.26-7.07, P=0.013) and homozygous long allele (OR=1.05, 95% CI: 0.62-1.78, P=0.848). The frequency of non-ht1 was significantly increased in patients with serositis (P<0.0001, OR=2.42, 95% CI: 1.55-3.80). In conclusion, the high expression promoter genotype is associated with SLE in Chinese.

Patients with systemic lupus erythematosus are deficient in complement-dependent prevention of immune precipitation

OBJECTIVE

A functional deficiency of complement has been implicated but not conclusively demonstrated in the pathogenesis of systemic lupus erythematosus (SLE). To test this, we studied several aspects of complement in 44 patients with SLE, 46 patients with rheumatoid arthritis and 102 blood donors.

METHODS

Prevention of immune precipitation (PIP) was measured by an enzyme immunoassay, levels of C1q, C4 and C3 by rocket immunoelectrophoresis, C4A, C4B and C3d by enzyme-linked immunosorbent assay (ELISA), complement haemolysis (CH50) by standard methods and C4 allotypes by high-voltage agarose electrophoresis and sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE).

RESULTS

PIP was significantly reduced in SLE (P<0.001); the defect was revealed by a sensitive assay measuring this function of complement but not by the other tests employed. The patients were clinically well at the time of study, and levels of C3d, which have been shown to correlate with disease activity, were normal. The defect was more common in patients with early disease (P = 0.009), supporting a role in aetiology or early pathophysiology. PIP was positively correlated with levels of C4 (P = 3 x 10(-5)) and in particular the C4A isotype (P = 9 x 10(-10)) whereas C4B was redundant.

CONCLUSIONS

Our results reveal a defect in prevention of immune precipitation in SLE that is apparent at an early stage in the disease and correlates with low levels of C4A. These results indicate that subtle deficiencies of complement may predispose to SLE.

Laboratory evaluation in neck pain

Laboratory investigations for neck pain play a minor role in most cases. When clinical suspicion of infection or tumor arises, however, laboratory testing can provide definitive information to direct the patient's care. Specialized laboratory testing including autoantibody titers can be useful in confirming and categorizing inflammatory arthritides. Judicious use of laboratory tests greatly enhances the physician's ability to provide appropriate care.

The genetics of systemic lupus erythematosus: putting the pieces together

With lambda(s) estimates of 10 to 20 and other evidence of familial aggregation, as well as a monozygotic twin concordance rate >20, systemic lupus erythematosus (SLE) would appear to be a very promising phenotype using modern genetic approaches. Indeed, genetic associations are already known at numerous candidate loci including various HLA alleles, complement component genes, Fcgamma receptors, and others, and murine genetic studies of lupus models have provided additional candidate genes and potential syntenic linkages to evaluate in man. The completed genetic linkage studies performed on various collections of pedigrees multiplex for SLE have identified 60 susceptibility loci with varying degrees of evidence for linkage in man. Seven of these meet or exceed the threshold for significant linkage (LOD > or = 3.3 or P < or = 0.00005) at 1q22-23, 1q41, 2q37, 4p16, 6p21-11, 16q13 and 17p13. In addition, these linkages usually dominate in one ethnicity or another, suggesting that the responsible polymorphisms, once identified, will also vary by ethnicity. Evidence that these linkages can be reproduced range from outright independent confirmation (1q41, 4p16 and 6p21) to additional suggestive evidence in the genomic region of the purported linkage (1q22-23 and 2q37). The results now available suggest that human lupus genetics are robust and that gene identification should be possible using existing genetic approaches and technologies.

Evidence for a susceptibility gene (SLEH1) on chromosome 11q14 for systemic lupus erythematosus (SLE) families with hemolytic anemia

Hemolytic anemia is a forme fruste of systemic lupus erythematosus (SLE), being observed months or even years before the onset of other clinical manifestations in some patients. We hypothesized that hemolytic anemia in those SLE-affected patients would identify a group of SLE pedigrees that share a high degree of genetic homogeneity. From 160 multiplex SLE pedigrees, we sought evidence for linkage in 35 (16 African-American, 17 European-American, and 2 Hispanic) who had at least one SLE-affected patient with hemolytic anemia. Significant linkage was present at 11q14 in the 16 African-American pedigrees, yielding a maximum two-point logarithm of odds (LOD) score of 4.5 at D11S2002. The segregation pattern of SLE in these African-American pedigrees suggested a dominant mode of inheritance and, when maximized across penetrance and disease allele frequencies, produced a multipoint LOD of 4.7. Multipoint analysis yielded a multipoint heterogeneity LOD score of 3.6 (alpha = 0.63), again with maximum LOD at D11S2002. Finally, markers typed 7 centimorgans to either side of D11S2002 achieved LOD scores of 3 or better by using the maximized model, supporting linkage to 11q14. Clearly, pedigree ascertainment based on select clinical manifestations is an important tool, capable of revealing otherwise cryptic genetic linkages in complex genetic diseases. Thus, we show strong evidence for an SLE susceptibility gene, SLEH1, near D11S2002 in African-American pedigrees multiplex for SLE that have at least one SLE-affected patient with hemolytic anemia.

Office evaluation of children with recurrent infection

This discussion provides an overview of the diagnostic approach to children with recurrent infections for the evaluation of a possible immunodeficiency. This article sets the stage for more detailed discussions of specific immunodeficiencies and therapeutic approaches used to reconstitute immune function in patients with these disorders.

Long PCR detection of the C4A null allele in B8-C4AQ0-C4B1-DR3

The genes coding for the two components of complement 4 (C4), C4A and C4B, are located within the major histocompatibility complex (MHC) on the short arm of chromosome 6. Several studies have shown that deficiency of C4A is associated with systemic lupus erythematosus (SLE), rheumatoid arthritis and scleroderma. A large deletion covering most of the C4A gene and the 21-hydroxylase-A (21-OHA) pseudogene found on the extended haplotype B8-C4AQ0-C4B1-DR3 is estimated to account for approximately two-thirds of C4A deficiency in Caucasian SLE patients. Detection of this C4A null allele has been technically difficult due to the high degree of homology between C4A and C4B, with protein analysis and restriction fragment length polymorphism (RFLP) analysis using Southern blotting being the only approaches available. In this study, a long PCR strategy was used to rapidly genotype for the C4A deletion through specific primer design. The methodology makes use of the unique sequence of the G11 gene upstream of C4A and the sequence of a 6.4 kb retrotransposon, the human endogenous retrovirus HERV-K(C4), which is present in intron 9 of C4A but absent in the case of the deletion.

Generalized lupus erythematosus profundus in a patient with genetic partial deficiency of C4

Lupus erythematosus profundus (LEP) is an unusual variant of cutaneous lupus erythematosus (CLE)that is characterized by chronic, recurrent inflammation of the subcutaneous tissue leading to fibrosis. It is found in the settings of both discoid and systemic lupus erythematosus. Generalized forms are extremely rare. We present a case of generalized LEP associated with genetic partial C4-deficiency.

Generalized lupus panniculitis and antiphospholipid syndrome in a patient without complement deficiency

Generalized chronic cutaneous lupus including lupus panniculitis in childhood is rare and usually occurs in the setting of genetic complement deficiencies. The association with antiphospholipid syndrome is even more rare. We report a 13-year-old girl with extensive lupus panniculitis since the age of 8 months and no evidence of complement deficiency. She recently developed antiphospholipid syndrome characterized by anticardiolipin antibodies and digital necrosis.

A Major Linkage Region on Distal Chromosome 4 Confers Susceptibility to Mouse Autoimmune Gastritis

Although much is known about the pathology of human chronic atrophic (type A, autoimmune) gastritis, its cause is poorly understood. Mouse experimental autoimmune gastritis (EAG) is a CD4+ T cell-mediated organ-specific autoimmune disease of the stomach that is induced by neonatal thymectomy of BALB/c mice. It has many features similar to human autoimmune gastritis. To obtain a greater understanding of the genetic components predisposing to autoimmune gastritis, a linkage analysis study was performed on (BALB/cCrSlc × C57BL/6)F2 intercross mice using 126 microsatellite markers covering 95% of the autosomal genome. Two regions with linkage to EAG were identified on distal chromosome 4 and were designated Gasa1 and Gasa2. The Gasa1 gene maps within the same chromosomal segment as the type 1 diabetes and systemic lupus erythematosus susceptibility genes Idd11 and Nba1, respectively. Gasa2 is the more telomeric of the two genes and was mapped within the same chromosomal segment as the type 1 diabetes susceptibility gene Idd9. In addition, there was evidence of quantitative trait locus controlling autoantibody titer within the telomeric segment of chromosome 4. The clustering of genes conferring susceptibility to EAG with those conferring susceptibility to type 1 diabetes is consistent with the coinheritance of gastritis and diabetes within human families. This is the first linkage analysis study of autoimmune gastritis in any organism and as such makes an important and novel contribution to our understanding of the etiology of this disease.

Immune complex glomerulonephritis in C4- and C3-deficient mice

In this study, we examined the roles of C4 and C3 in immune complex glomerulonephritis by actively immunizing C4-deficient (C4 -/-), C3 deficient (C3 -/-) and wild-type mice with apoferritin. Wild-type animals with an intact complement system produced anti-apoferritin IgG and IgM antibodies, and developed mesangial proliferative glomerulonephritis characterized by hypercellularity, matrix expansion, deposition of IgG, IgM, IgA and C3, and the presence of electron dense deposits. In the majority of animals, the peripheral capillaries also contained IgG, C3 and subendothelial and subepithelial electron dense deposits. In contrast to wild-type animals, all apoferritin-immunized C4 -/- and C3 -/- mice had serum cryoprecipitates containing polyclonal IgM and the variable presence of polyclonal IgG. These animals also developed immune complex glomerulonephritis, but their disease manifestations were distinctly different from that of their wild-type littermates. In apoferritin-immunized C4 -/- and C3 -/- mice, IgG was either absent or present in reduced quantities in glomeruli, yet IgM and IgA were present in greater intensity in glomeruli. Capillary wall IgG deposits were absent in all C4 -/- and C3 -/- animals. C4 -/- animals also had significant glomerular C3 deposition, hypercellularity and neutrophil infiltration, which were not present in C3 -/- animals. These results illustrate the complex interplay between the effects of complement to process immune complexes and to lead to inflammation and tissue injury.