Homozygous single nucleotide polymorphism of the complement C1QA gene is associated with decreased levels of C1q in patients with subacute cutaneous lupus erythematosus.

We report an association between a non-familial form of photosensitive Lupus-specific skin disease, subacute cutaneous lupus erythematosus (SCLE), and a new single nucleotide polymorphism (SNP) in the C1QA gene. We also describe an association between this SNP and lower levels of serum C1q. This SNP consists of adenine replacing the third guanine in the codon for aminoacid residue Gly70 (position excludes the 22 amino acid leading peptide) that is located in the second exon of the C1QA gene. We have designated this SNP C1qA-Gly70GGA (the GenBank sequence at this location is C1qA-Gly70GGG). A survey of 19 SCLE patients showed that 11 (58%) were homozygous for C1qA-Gly70GGA SNP, seven (37%) were heterozygous, and only one patient (5%) was homozygous for the GenBank sequence. In contrast, only 13 of 62 (21%) normal controls were homozygous for the C1qA-Gly70GGA SNP, 41 (66%) controls were heterozygous and eight (13%) controls were homozygous for the GenBank sequence. Thus, the C1qA-Gly70GGA SNP is strongly associated with SCLE (P-value = 0.005 by chi-square analysis with Yates correction). This SNP would traditionally be classified as clinically silent as it does not encode a different amino acid. However, our studies have suggested that this SNP appears to be associated with a functional abnormality of C1q expression since its presence correlates inversely with serum levels of C1q antigenic protein in both SCLE patients and normal controls. The mechanism by which this phenotypic change is associated with the translationally silent (synonymous) ClqA-Gly70GGA genetic variation is currently unknown.

C1 inhibitor: analysis of the role of amino acid residues within the reactive center loop in target protease recognition.

Previous analysis of a naturally occurring C1 inhibitor P2 mutant (Ala(443)-->Val) indicated a role for P2 in specificity determination. To define this role and that of other reactive center loop residues, a number of different amino acids were introduced at P2, as well as at P6 (Ala(439)) and P8'/9' (Gln(452)Gln(453)). Ala(439)-->Val is a naturally occurring mutant observed in a patient with hereditary angioedema. Previous data suggested that Gln(452)Gln(453) might be a contact site for C1s. Reactivity of the inhibitors toward target (C1s, C1r, kallikrein, beta factor XIIa, and plasmin) and nontarget proteases (alpha-thrombin and trypsin) were studied. Substitution of P2 with bulky or charged residues resulted in decreased reactivity with all target proteases. Substitution with residues with hydrophobic or polar side chains resulted in decreased reactivity with some proteases, but in unaltered or increased reactivity with others. Second order rate constants for the reaction with C1s were determined for the mutants with activities most similar to the wild-type protein. The three P2 mutants showed reductions in rate from 3.35 x 10(5) M(-1)s(-1) for the wild type to 1.61, 1.29, and 0.63 x 10(5) for the Ser, Thr, and Val mutants, respectively. In contrast, the Ala(439)-->Val and the Gln(452)Gln(453)-->Ala mutants showed little difference in association rates with C1s, in comparison with the wild-type inhibitor. The data confirm the importance of P2 in specificity determination. However, the P6 position appears to be of little, if any, importance. Furthermore, it appears unlikely that Gln(452)Gln(453) comprise a portion of a protease contact site within the inhibitor.

The globular heads of C1q specifically recognize surface blebs of apoptotic vascular endothelial cells.

Complement protein C1q is required to maintain immune tolerance. The molecular mechanism responsible for this link has not been determined. We have previously demonstrated that C1q binds directly and specifically to surface blebs of apoptotic human keratinocytes, suggesting that it may participate in clearance of self Ags generated during programmed cell death. Here, we demonstrate that C1q also binds directly to apoptotic blebs of vascular endothelial cells and PBMC. These apoptotic cells are recognized by the globular heads of C1q, which bind specifically to the surface blebs, and deposition increases as the blebs mature on the cell surface. These observations suggest that C1q may participate in the clearance of apoptotic cells from the circulation and from the walls of the vascular lumen. The interaction of surface blebs with the globular heads of C1q suggests that surface blebs may be capable of directly activating the classical pathway of complement under certain circumstances, generating C4- and C3-derived ligands for receptors such as CR1, CR2, CR3, and CR4. Appropriate recognition of apoptotic cells by C1q and targeted clearance of the molecular contents of surface blebs to complement receptors may be critical for the maintenance of immune tolerance.

Urticarial vasculitis.

Chronic or recurrent urticarial lesions are common in both primary care and referral medicine. Diagnosis and treatment are usually a challenge for both the patient and the medical practitioner. Most patients are eventually diagnosed with chronic idiopathic urticaria. IgG autoantibody to IgE receptor or IgE itself causes urticarial lesions in 30% of these patients. Only a minority (approximately 10%) of patients with chronic urticarial lesions have urticarial vasculitis. Although some cases are benign, urticarial vasculitis by itself can cause significant morbidity, and it is often a manifestation of a serious illness. Successful diagnosis and treatment of urticarial vasculitis requires careful assessment over time for underlying diseases like systemic lupus erythematosus, hypocomplementemic urticarial vasculitis syndrome, Sjögren's syndrome, and mixed cryoglobulinemia.

Antibodies to C1q in systemic lupus erythematosus: characteristics and relation to Fc gamma RIIA alleles.

Autoantibodies to the collagen-like region of the first complement component (C1qAB) are found in patients with systemic lupus erythematosus (SLE), particularly those with renal disease. In a cohort of 46 SLE patients with diffuse proliferative glomerulonephritis, we found declining C1qAB titers in 77% of treatment responders and in only 38% of treatment non-responders (P < 0.03). To further characterize this autoantibody, we tested 240 SLE patients for the presence of C1qAB. Positive titers were found in 44% of patients with renal disease and 18% of patients without renal disease (chi2 P < 0.0003). Analysis of IgG subclass revealed IgG2 C1qAB alone in 34%, IgG1 C1qAB alone in 20%, and both IgG1 and IgG2 in 46% of patients. Fewer than 10% of patients had measurable titers of IgG3 or IgG4 C1qAB. The pathogenic role of these IgG2-skewed C1qAB may relate to impaired immune complex clearance by the mononuclear phagocyte system: IgG2 antibodies are efficiently recognized by only one IgG receptor, the H131 allele of Fc gamma RIIa (Fc gamma RIIa-H131). In contrast, Fc gamma RIIa-R131, which is characterized by minimal IgG2 binding, has recently been associated with lupus nephritis. In our C1qAB positive patients, the presence of Fc gamma RIIA-R131 was associated with an increased risk for renal disease. Autoantibodies to C1q may have pathogenic significance in SLE patients with genetic defects in the ability to clear IgG2 containing immune complexes.

IgG autoantibodies to complement C1q in pediatric-onset systemic lupus erythematosus.

OBJECTIVE: Antibodies to C1q (aC1q) have been found in up to 50% of adult patients with systemic lupus erythematosus (SLE) and have been associated with proliferative glomerulonephritis. We investigated the prevalence and clinical significance of aC1q in pediatric SLE. METHODS: Antibodies to C1q, measured by an ELISA method, were evaluated in 29 patients with childhood-onset SLE, 26 females and 3 males, aged 7.5 to 19.6 years. RESULTS: Seventeen (59%) of the 29 patients were initially positive for aC1q. No correlation was found between either the presence or titer of aC1q and any of the clinical manifestations, including nephritis. However, a significant correlation was observed between aC1q levels and anti-double-stranded DNA antibodies and C3 values. Serial determinations of aC1q in 23 patients showed a progressive decline in the titers with few significant fluctuations. Antibodies to C1q were not a reliable predictor of increased SLE activity, since they increased or became detectable in only 50% of the pre-flare sera. CONCLUSION: Antibodies to C1q were frequently positive in our patients with pediatric SLE and were correlated with laboratory variables of disease activity. However, unlike in adults with SLE, a high correlation between aC1q and glomerulonephritis was not found in these pediatric patients.

Serum complement determinations in patients with quiescent systemic lupus erythematosus.

OBJECTIVE: To determine whether complement component analyses during a period of inactive disease can define clinically important subgroups and predict morbidity in patients with systemic lupus erythematosus (SLE). METHODS: We identified 277 patients with SLE whose disease became clinically inactive at some point after diagnosis. Serum samples were obtained at that time and tested for total complement activity (CH100) and antigenic levels of C1q, C1r, C1s, C3 and C4. Results of complement determinations were correlated with demographic characteristics and clinical findings in the followup period (mean observation period 4.25 years). RESULTS: We identified 25 (9%) patients with multiple complement determinations below the normal range. 24 other patients (8.5%) had a very low level of a single complement component. The group with multiple complement determinations below the normal range was much more likely than the normocomplementemic SLE controls to progress to renal insufficiency. In other respects, complement component determinations were neither reflective nor predictive of clinical course. CONCLUSION: In this group of patients with inactive SLE, complement component analyses did not generally correlate with longterm outcome; however, multiple low complement component determinations during disease quiescence was associated with increased risk of renal insufficiency.

Induction of monocyte expression of tumor necrosis factor alpha by the 30-kD alpha antigen of Mycobacterium tuberculosis and synergism with fibronectin.

Native 30-kD antigen, also known as alpha antigen, is a fibronectin-binding protein that is secreted by live Mycobacterium tuberculosis. This antigen may play an important biological role in the host-parasite interaction since it elicits delayed type hypersensitivity response and protective immunity in vivo and T lymphocyte blastogenesis and IFN-gamma production in vitro. In the present study, we show that, TNF-alpha protein is produced in monocyte culture supernatants in response to 30-kD antigen and the level is as high as that to purified protein derivative of M. tuberculosis. This stimulatory effect was not due to contamination with either bacterial lipopolysaccharide or mycobacterial lipoarabinomannan. The preincubation of monocytes with plasma fibronectin significantly enhanced the release of TNF-alpha into the culture supernatants in response to 30-kD antigen. This effect was blocked by polygonal antibody to plasma fibronectin. In contrast, the monocytic cell line U937 failed to release TNF-alpha protein in the culture supernatants in response to 30-kD antigen with or without preincubation with plasma fibronectin. To determine whether this observation was due to differential binding of the 30-kD to fibronectin on these cells, a cell based ELISA was used. Pretreatment of monocytes with fibronectin enhanced their binding of the 30-kD antigen. U937 cells bound the 30-kD antigen weakly with or without fibronectin pretreatment. These results indicate that 30-kD antigen which is a known secretary antigen of M. tuberculosis is a stimulus for human monocytes to express TNF-alpha and that stimulatory effect may be mediated through plasma fibronectin.

Autoantibodies in systemic lupus erythematosus and urticarial vasculitis.

OBJECTIVE: Urticarial vasculitis (UV) is both a primary disorder and a cutaneous vasculitic manifestation in patients with connective tissue diseases. We examined the prevalence of autoantibodies to vascular endothelial cells (aECA) and anti-Clq antibodies in patients with UV. METHODS: ELISA were used to detect aECA and anti-Clq autoantibodies, and we tested for correlation with UV in 4 patient groups: healthy controls, patients with systemic lupus erythematosus (SLE) with and without UV, patients with primary systemic vasculitides with UV, and patients with hypocomplementemic urticarial vasculitis syndrome (HUVS). RESULTS: aECA were detected in 82% of patients with SLE with UV and 70% of patients with HUVS. In contrast, aECA were found in 32% of patients with SLE without UV and 14% of patients with primary UV. Anti-Clq antibodies were present in all patients with HUVS, but in < 20% in the other 3 groups. Antineutrophil cytoplasmic antibodies were detected in only one patient. CONCLUSION: Although the development of UV is likely to be multifactorial, the high prevalence of aECA in HUVS and SLE with UV suggests that this antibody is associated with vasculitis and may have a role in the pathogenesis of UV in these patients.

Sarcoid myopathy in a patient with human immunodeficiency virus infection.

Although neither sarcoidosis nor HIV infection is rare, only eight patients with both diseases have been described. None of the eight had sarcoid myopathy. We describe a patient who had HIV infection and decreased CD4+ T-lymphocytes as well as sarcoidosis with muscle involvement. During 3 years of observation, primary sarcoidosis remitted and myopathic symptoms were controlled with prednisone. No opportunistic infections occurred during more than 3 years of prednisone therapy.

Unique C1 inhibitor dysfunction in a kindred without angioedema. II. Identification of an Ala443-->Val substitution and functional analysis of the recombinant mutant protein.

We have determined the cause of an unusual C1 inhibitor abnormality in a large kindred. We previously found that half of serum C1 inhibitor molecules in affected kindred members are normal. The other half complexed with C1s but showed little complex formation with C1r. These molecules also appeared to be relatively resistant to digestion by trypsin. Taken together, the findings suggested that members of this kindred are heterozygous for an unusual C1 inhibitor mutation. Sequencing of genomic DNA from the kindred revealed that thymine has replaced cytosine in the codon for Ala443 (P2 residue) in one C1 inhibitor allele, resulting in substitution with a Val residue. To test the effect of this substitution, a mutant C1 inhibitor containing Ala443-->Val was constructed by site-directed mutagenesis and expressed in COS-1 cells. Both the Ala443-->Val mutant and the wild-type C1 inhibitor complexed completely with C1s, kallikrein, and coagulation Factor XIIa after incubation at 37 degrees C for 60 min. In contrast, the mutant inhibitor failed to complex completely with C1r under the same conditions. Time course analysis showed that the ability of the mutant to complex with C1s is also impaired: although it complexed completely in 60 min, the rate of complex formation during a 0-60-min incubation was decreased compared with wild-type C1 inhibitor. The mutant inhibitor also formed a complex with trypsin, a serine protease that cleaves, and is not inhibited by, wild-type C1 inhibitor. The Ala443-->Val mutation therefore converts C1 inhibitor from a substrate to an inhibitor of trypsin. These studies emphasize the role of the P2 residue in the determination of target protease specificity.

Hypocomplementemic urticarial vasculitis syndrome. Clinical and serologic findings in 18 patients.

We identify and describe clinical findings in hypocomplementemic urticarial vasculitis syndrome (HUVS), an uncommon to rare illness related to systemic lupus erythematosus (SLE). A patient with recurrent, idiopathic urticaria-like lesions was diagnosed as having HUVS if a lesional biopsy showed leukocytoclastic vasculitis, the serum C1q was markedly decreased, and antibody to C1q was detected in the patient's serum. The clinical characteristics, serologic findings, and outcome of patients who met these criteria were determined from prospective and retrospective data, including hospital and office records, patient interviews, previously banked serum samples, and freshly drawn sera. Eighteen patients with HUVS were identified, and high incidences of angioedema, ocular inflammation, glomerulonephritis, and obstructive pulmonary disease were found. Renal and lung biopsies showed mesangial or membranoproliferative glomerulonephritis and severe pulmonary emphysema without vasculitis. Pulmonary function was measured in 17 patients, 11 of whom had dyspnea. All dyspneic patients had moderate to severe airflow obstruction, which progressed in all 11 and subsequently improved in only 1. Six of these 11 patients died of respiratory failure, 1 underwent lung transplantation, and 3 of the remaining 4 have moderately severe to life-threatening respiratory insufficiency. Treatment did not appear to alter the progression of obstructive lung disease. In contrast, renal insufficiency improved with treatment in 2 of 2 patients. Angioedema, ocular inflammation, obstructive lung disease, and glomerulonephritis appear to be common in HUVS, and lung disease causes substantial morbidity and mortality. The pathogenesis of HUVS may involve humoral autoimmunity, although it is not clear how autoimmunity would participate in development of obstructive lung disease. Cigarette smoking appears to be a risk factor for fatal lung disease in HUVS. All patients with HUVS should be made aware of this possibility and should be advised, encouraged, and helped to avoid tobacco smoke.

Hypocomplementemic urticarial vasculitis syndrome in identical twins.

Hypocomplementemic urticarial vasculitis syndrome (HUVS) is a syndrome of recurrent urticarial vasculitis, arthralgia/arthritis, and hypocomplementemia. Angioedema, ocular inflammation, glomerulonephritis, and obstructive lung disease are other clinical findings. Although the etiology of HUVS is unknown, its resemblance to systemic lupus erythematosus (SLE) suggests a similar pathogenesis. SLE is known to occur in identical twins. This is the first report of a pair of identical twins with HUVS. Concordance for HUVS in identical twins suggests that the pathogenesis of the disease involves abnormal genetic immunoregulation.

Hypocomplementemic urticarial vasculitis syndrome with severe systemic manifestations.

We describe two children with clinical and laboratory features of hypocomplementemic urticarial vasculitis syndrome. Both patients had severe, life-threatening manifestations: rapidly progressive glomerulonephritis (patient 1) and pulmonary hemorrhage (patient 2). We conclude that this syndrome may be a potentially severe multisystem disease.

Unique C1 inhibitor dysfunction in a kindred without angioedema. I. A mutant C1 INH that inhibits C1-s but not C1-r.

We have described hereditary incomplete deficiency of the fourth component of complement (C4) in 10 members of a large kindred. C4 deficiency in this kindred is not linked to C4 loci in the HLA region. C4 synthesis is decreased, and C4 catabolism is normal in kindred members with low serum C4 levels. We have discovered a uniquely dysfunctional C1 inhibitor in all C4-deficient members of this kindred. C1 inhibitor dysfunction is revealed by incubating sera of affected members with EDTA, which destroys all C4 activity in these sera, but not in normal sera or sera from individuals with partial C4 deficiencies. The M(r) of C1 inhibitor purified from affected members is normal, but approximately 50% of this C1 inhibitor resists cleavage by trypsin (0.14 microM) at arg444, suggesting a substitution at this position. Moderate increases in trypsin, however, result in cleavage of the resistant molecules, which would not be expected if arg444 were the site of the mutation. All molecules in C1 inhibitor purified from affected members' plasma bind to activated C1s (C1-s), but approximately 50% of molecules in these preparations do not bind to activated C1r (C1r). These findings show that affected kindred members have a unique mutation in C1 inhibitor. The mutant C1 inhibitor does not prevent the activation of C1s by C1-r when serum Ca2+ is chelated by EDTA, but its inhibition of C1-s is normal in vivo, as shown by normal C2 levels, normal C4 catabolism, and absence of angioedema in C4-deficient members. The nature of the mutation, its selective failure to inhibit C1-r, and its relationship to decreased C4 synthesis remain to be defined.

Recurrent angioedema and urticaria.

The case reported here illustrates the life-threatening aspects of angioedema and the need to thoroughly investigate the possible causes of this clinical finding. As discussed, the causes of angioedema are numerous. Commonly implicated in drug-induced angioedema are antihypertensive ACE inhibitor drugs, as was originally thought with this patient. Because of her skin lesions and macrocytic anemia, further studies were done. These studies led to a diagnosis of hypocomplementemic urticarial vasculitis syndrome, an uncommon to rare form of acquired angioedema, urticarial vasculitis, arthritis, and obstructive airway disease associated with the production of autoantibodies to C1q. It is an autoimmune disorder related to but separate from SLE.

The clinical spectrum of the arthropathy associated with hidradenitis suppurativa and acne conglobata.

Patients with hidradenitis suppurativa/acne conglobata attending a university medical center were evaluated for the presence of an associated arthritis. Of 44 subjects, 21 had objective evidence of inflammatory arthropathy. Of these 21, all adults, 11 were women and 17 black Americans; clinically, 18 had peripheral arthritis, 15 axial arthropathy and 12 both. Clinical and laboratory findings were characteristic of those seen in other seronegative spondyloarthropathies, except for lack of association with HLA-B27.

IgG autoantibody to the collagen-like region of Clq in hypocomplementemic urticarial vasculitis syndrome, systemic lupus erythematosus, and 6 other musculoskeletal or rheumatic diseases.

We previously found that the Clq precipitin in sera from patients with hypocomplementemic urticarial vasculitis syndrome is an IgG autoantibody to Clq. We report here a prevalence study of this autoantibody in 162 patients with musculoskeletal or rheumatic diseases including hypocomplementemic urticarial vasculitis syndrome, systemic lupus erythematosus (SLE), and rheumatoid arthritis uncomplicated by vasculitis. The autoantibody, which binds only to the collagen-like region of Clq, was found almost exclusively in hypocomplementemic urticarial vasculitis syndrome (100%) and SLE (35%) sera. Our results support the idea that among rheumatic diseases, anti-Clq autoantibody develops in disorders characterized by immune complex mediated injury, particularly of cutaneous and glomerular microvasculature.

Comparison of autoantibodies to the collagen-like region of C1q in hypocomplementemic urticarial vasculitis syndrome and systemic lupus erythematosus.

Hypocomplementemic urticarial vasculitis syndrome (HUVS) is an apparent autoimmune disorder that resembles SLE. We previously showed that C1q precipitins in HUVS sera are IgG autoantibody to human C1q. We have compared HUVS anti-C1q autoantibody to a similar autoantibody in the serum of some patients with SLE. As with anti-C1q autoantibody in SLE sera, the HUVS autoantibody binds only to the collagen-like region (CLR) of C1q. In both HUVS and SLE, IgG2 is the predominant subclass of IgG autoantibody and IgM autoantibody to C1q is uncommon. In both diseases, anti-C1q autoantibodies bind preferentially to surface-adsorbed C1q or CLR fragments compared to these antigens in solution. Finally, when HUVS or SLE autoantibodies were added to CLR-coated wells already bound, respectively, by SLE or HUVS autoantibodies, no increases in CLR binding were observed, suggesting that HUVS and SLE autoantibodies to C1q bind to the same CLR epitope(s).