Complement C4, Infections, and Autoimmune Diseases.

Complement C4, a key molecule in the complement system that is one of chief constituents of innate immunity for immediate recognition and elimination of invading microbes, plays an essential role for the functions of both classical (CP) and lectin (LP) complement pathways. Complement C4 is the most polymorphic protein in complement system. A plethora of research data demonstrated that individuals with C4 deficiency are prone to microbial infections and autoimmune disorders. In this review, we will discuss the diversity of complement C4 proteins and its genetic structures. In addition, the current development of the regulation of complement C4 activation and its activation derivatives will be reviewed. Moreover, the review will provide the updates on the molecule interactions of complement C4 under the circumstances of bacterial and viral infections, as well as autoimmune diseases. Lastly, more evidence will be presented to support the paradigm that links microbial infections and autoimmune disorders under the condition of the deficiency of complement C4. We provide such an updated overview that would shed light on current research of complement C4. The newly identified targets of molecular interaction will not only lead to novel hypotheses on the study of complement C4 but also assist to propose new strategies for targeting microbial infections, as well as autoimmune disorders.

IgG4-Related Disease Manifesting as Hypocomplementemic Tubulointerstitial Nephritis: A Rare Case Report and Literature Review.

Immunoglobulin G4-related disease (IgG4-RD) is a chronic fibrosing inflammatory systemic disorder that has been recognized relatively recently in the medical literature. Little is known about the exact disease pathogenesis and epidemiology. IgG4-RD may be asymptomatic or may have minimal symptoms or involve multiple organs with overt symptoms. The different phenotypes of IgG4-RD can lead to delayed or incorrect diagnosis. We report the case of a 66-year-old male with coal worker's pneumoconiosis who presented with progressive kidney disease and was diagnosed with tubulointerstitial nephritis due to IgG4-RD. The patient was noted to have progressive kidney disease, skin involvement, worsening interstitial lung disease, complete vision loss in the left eye, and retroperitoneal fibrosis. Serologic workup revealed elevated inflammatory markers, IgG4 and IgG1 levels, and hypocomplementemia. A tissue biopsy helped us establish a definitive diagnosis of IgG4-RD and initiate treatment with glucocorticoids to prevent further progression of kidney disease and other end-organ damage.

Hereditary and acquired angioedema.

Hereditary angioedema (HAE) is an autosomal dominant disorder defined by a deficiency of functional C1 esterase inhibitor (C1-INH). Acquired angioedema is due to either consumption (type 1) or inactivation (type 2) of CI-INH. Both HAE and acquired angioedema can be life-threatening. Of the three types of HAE, type 1 is most common, occurring in approximately 85% of patients and characterized by decreased production of C1-INH, which results in reduced functional activity to 5-40% of normal. Type 2 occurs in 15% of cases; C1-INH is detectable in normal or elevated quantities but is dysfunctional. Also, HAE with normal CI-INH (previously called type 3 HAE) is rare and characterized by normal complement studies. Specific genetic mutations have been linked to factor XII, angiopoietin-1, and plasminogen gene. Patients with unknown mutations are classified as unknown. The screening test for types 1 and 2 is complement component C4, which is low to absent at times of angioedema and during quiescent periods. A useful test to differentiate HAE from acquired angioedema is C1q protein, which is normal in HAE and low in acquired angioedema. The management of HAE has been transformed with the advent of disease-specific therapies. On-demand therapy options include plasma and recombinant C1-INH for intravenous infusion; ecallantide, an inhibitor of kallikrein; and icatibant, a bradykinin ß2 receptor antagonist, both administered subcutaneously. For long-term prophylaxis, intravenous or subcutaneous C1-INH enzyme replacement and lanadelumab, a monoclonal antibody against kallikrein that is administered subcutaneously, are effective agents.

Post-transplant hypocomplementemia: A novel marker of cardiovascular risk in kidney transplant recipients?

BACKGROUND AND AIMS: Cardiovascular disease (CVD) is a leading cause of mortality after kidney transplantation (KT). The potential role of the complement system in the pathogenesis of post-transplant CVD remains unexplored. METHODS: Serum complement (C3 and C4) levels were measured at baseline and post-transplant months 1 and 6 in 447 kT recipients. The study outcome was post-transplant atherothrombotic event (PAE), a composite of acute coronary syndrome, critical peripheral arterial disease, stroke and/or transient ischemic attack. RESULTS: After a median follow-up of 4.2 years, 48 PAEs occurred in 43 patients (cumulative incidence: 9.6%; incidence rate: 2.6 events per 100 transplant-years). No differences were found in C3 and C4 levels at baseline or month 1 between patients with or without PAE. However, C3 levels at month 6 were significantly lower in patients developing PAE beyond that point (i.e., late PAE) (96.9 ±â€¯22.3 vs. 109.6 ±â€¯24.0 mg/dL; p = 0.013). The presence of C3 hypocomplementemia at month 6 was associated with a lower PAE-free survival (p = 0.002). After adjusting for conventional CVD risk factors and acute graft rejection, C3 hypocomplementemia at month 6 remained as an independent risk factor for late PAE in all the exploratory models (minimum hazard ratio: 3.24; p = 0.011). With respect to a model exclusively based on clinical variables, the inclusion of C3 levels at month 6 improved predictive capacity (areas under ROC curves: 0.788 and 0.812, respectively). CONCLUSIONS: Post-transplant monitoring of serum C3 levels might be useful to identify KT recipients at increased risk of CVD.

A Novel Mechanism for Generating the Interferon Signature in Lupus: Opsonization of Dead Cells by Complement and IgM.

OBJECTIVE: In vitro studies suggest that the type I interferon (IFN) signature seen in most lupus patients results from Fcγ receptor-mediated uptake of nucleic acid-containing immune complexes by plasmacytoid dendritic cells and engagement of endosomal Toll-like receptors. The aim of this study was to reexamine the pathogenesis of the IFN signature in vivo. METHODS: Lupus was induced in mice by injecting pristane. Some mice were treated with normal immunoglobulin or with cobra venom factor to deplete complement. The IFN signature was evaluated by polymerase chain reaction. The IFN signature also was determined in C4-deficient patients and control subjects. RESULTS: Wild-type C57BL/6 mice with pristane-induced lupus developed a strong IFN signature, which was absent in immunoglobulin-deficient (µMT), C3-/- , and CD18-/- mice. Intravenous infusion of normal IgM, but not IgG, restored the IFN signature in µMT mice, and the IFN signature in wild-type mice was inhibited by depleting complement, suggesting that opsonization by IgM and complement is involved in IFN production. Consistent with that possibility, the levels of "natural" IgM antibodies reactive with dead cells were increased in pristane-treated wild-type mice compared with untreated controls, and in vivo phagocytosis of dead cells was impaired in C3-deficient mice. To examine the clinical relevance of these findings, we identified 10 C4-deficient patients with lupus-like disease and compared them with 152 C4-intact patients and 21 healthy controls. In comparison with C4-intact patients, C4-deficient patients had a different clinical/serologic phenotype and lacked the IFN signature. CONCLUSION: These studies define previously unrecognized roles of natural IgM, complement, and complement receptors in generating the IFN signature in lupus.

Low C4, C4A and C4B gene copy numbers are stronger risk factors for juvenile-onset than for adult-onset systemic lupus erythematosus.

OBJECTIVE: Complete deficiency of Complement C4 component is a strong genetic risk factor for SLE. C4 is encoded by two different genes, C4A and C4B, which show considerable gene copy number (GCN) variation. This study investigates the association of total C4, C4A and C4B GCN with JSLE. METHODS: Ninety JSLE patients, 170 adult-onset SLE (aSLE) patients and 200 healthy individuals were evaluated for C4A and C4B GCN by quantitative real-time PCR. RESULTS: JSLE patients had lower GCN for C4A (mean = 1.7; 95% CI: 1.5, 1.9) and C4B (mean = 1.5; 95% CI: 1.3, 1.6) compared with healthy individuals (mean C4A = 2.3; 95% CI: 2.2, 2.5, P < 0.001; C4B = 2.0; 95% CI: 1.8, 2.1; P < 0.001) or with aSLE patients (mean C4A = 1.9; 95% CI: 1.8, 2.1, P = 0.006; mean C4B = 1.8; 95% CI: 1.7, 1.9, P < 0.001). Low total C4 GCN (<4 copies) was more frequent in JSLE than in healthy individuals (59% vs 28%; P < 0.001). The same was observed for low C4A (⩽1 copy) (52% vs 18%; P < 0.001) and for low C4B (60% vs 31%; P < 0.001). JSLE had a stronger association with low total C4 (OR = 3.68, 95% CI: 2.19, 6.20), C4A (OR = 4.98, 95% CI: 2.88, 8.62) and C4B (OR = 3.26; 95% CI: 1.95, 5.47) than aSLE (C4 OR = 2.03; 95% CI: 1.32, 3.13; C4A OR = 2.36; 95% CI: 1.46, 3.81; C4B OR = 1.13; 95% CI: 0.73, 1.74). In addition, pericarditis in JSLE patients was associated with low C4 (OR = 4.13; 95% CI: 1.02, 16.68; P = 0.047) and low C4A (OR = 5.54; 95% CI: 1.37, 22.32; P = 0.016). CONCLUSION: Low total C4, C4A and C4B GCN were associated with a stronger risk for developing JSLE than aSLE. Additionally, low total C4 and C4A GCN are risk factors for pericarditis in JSLE.

Gene copy-number variations (CNVs) of complement C4 and C4A deficiency in genetic risk and pathogenesis of juvenile dermatomyositis.

OBJECTIVE: Complement-mediated vasculopathy of muscle and skin are clinical features of juvenile dermatomyositis (JDM). We assess gene copy-number variations (CNVs) for complement C4 and its isotypes, C4A and C4B, in genetic risks and pathogenesis of JDM. METHODS: The study population included 105 patients with JDM and 500 healthy European Americans. Gene copy-numbers (GCNs) for total C4, C4A, C4B and HLA-DRB1 genotypes were determined by Southern blots and qPCRs. Processed activation product C4d bound to erythrocytes (E-C4d) was measured by flow cytometry. Global gene-expression microarrays were performed in 19 patients with JDM and seven controls using PAXgene-blood RNA. Differential expression levels for selected genes were validated by qPCR. RESULTS: Significantly lower GCNs and differences in distribution of GCN groups for total C4 and C4A were observed in JDM versus controls. Lower GCN of C4A in JDM remained among HLA DR3-positive subjects (p=0.015). Homozygous or heterozygous C4A-deficiency was present in 40.0% of patients with JDM compared with 18.2% of controls (OR=3.00 (1.87 to 4.79), p=8.2×10(-6)). Patients with JDM had higher levels of E-C4d than controls (p=0.004). In JDM, C4A-deficient subjects had higher levels of E-C4d (p=0.0003) and higher frequency of elevated levels of multiple serum muscle enzymes at diagnosis (p=0.0025). Microarray profiling of blood RNA revealed upregulation of type I interferon-stimulated genes and lower abundance of transcripts for T-cell and chemokine function genes in JDM, but this was less prominent among C4A-deficient or DR3-positive patients. CONCLUSIONS: Complement C4A deficiency appears to be an important factor for the genetic risk and pathogenesis of JDM, particularly in patients with a DR3-positive background.

A role of oestrogen in aggravating SLE-like syndrome in C4-deficient mice.

BACKGROUND: As one of the epigenetic factors, oestrogen is considered to be a predisposing factor that is associated with a susceptibility to autoimmune disease development in women including systemic lupus erythematosus (SLE). Here, we proposed that oestrogen is also imparted in a post-lupus symptomatic enhancement as studied in the C4-deficient (C4-/-) mice model known to develop SLE-like symptoms. METHODS: Fifty-six C4 knockout mice were ovariectomised (OVX) to eliminate the effect of endogenous feminine hormones followed by 17-ß oestradiol (E2) administration in both dose- and time-dependent manners. Histopathological features of kidneys and spleens were studied by histological and immunofluorescent staining. The relative expression levels of IgG and IgM were measured densitometrically on their immunoreactive bands and the level of IgG-anti-double stranded (ds) DNA was measured by ELISA. RESULTS: E2-treated mice displayed a gradual increase in immune complex deposition (both IgG and IgM) in glomeruli and proximal convoluted tubules. An increased reactivity of autoantibodies against dsDNA correlated with increasing doses and longer exposure to E2 treatments. In addition, enlargement of the spleen (splenomegaly) was also observed in E2-treated mice. CONCLUSIONS: Our results support the hypothesis that oestrogen aggravates severity of the SLE-like symptoms in C4-deficient mice.

Primary complement and antibody deficiencies in autoimmune rheumatologic diseases with juvenile onset: a prospective study at two centers.

BACKGROUND: Our aim was to investigate the prevalence and clinical relevance of inherited complement and antibody deficiency states in a large series of patients with various autoimmune rheumatologic diseases (ARD) with juvenile onset. METHODS: A total number of 117 consecutive patients from 2 tertiary referral hospitals were included in the study. All patients underwent genetic screening for type I C2 deficiency and C4 allotyping. Serum levels of immunoglobulin classes measured systematically throughout their regular medical care were recorded retrospectively. RESULTS: Our cohort of patients included 84 with juvenile idiopathic arthritis (JIA), 21 with systemic lupus erythematosus (SLE), 6 with systemic vasculitis, 2 with juvenile scleroderma, 2 with idiopathic uveitis, 1 with mixed connective tissue disease and 1 with SLE/scleroderma overlap syndrome. We have found 16 patients with evidence of primary immunodeficiency in our series (13.7%), including 7 with C4 deficiency, 5 with selective IgA deficiency, 3 with C2 deficiency and 2 with unclassified hypogammaglobulinemia (one also presented C4D). Of the 84 patients with JIA, 4 (4.8%) had a complement deficiency, which was less prevalent than in the SLE cohort (23.8%), but all of them have exhibited an aggressive disease. Most of our patients with primary antibody deficiencies showed a more complicated and severe disease course and even the co-occurrence of two associated autoimmune diseases (SLE/scleroderma overlap syndrome and SLE/autoimmune hepatitis type 1 overlap). CONCLUSIONS: Our findings among others demonstrate that complement and immunoglobulin immunodeficiencies need careful consideration in patients with ARD, as they are common and might contribute to a more severe clinical course of the disease.

Comparison of immune manifestations between refractory cytopenia of childhood and aplastic anemia in children: A single-center retrospective study.

This retrospective single-center study assessed the incidence and clinical features of immune manifestations of refractory cytopenia of childhood (RCC) and childhood aplastic anemia (AA). We evaluated 72 children with RCC and 123 with AA between February 2008 and March 2013. RCC was associated with autoimmune disease in 4 children, including 1 case each with autoimmune hemolytic anemia, rheumatoid arthritis, systemic lupus erythematosus, and anaphylactoid purpura. No children with AA were diagnosed with autoimmune diseases. Immune abnormalities were common in both RCC and AA; the most significant reductions were in the relative numbers of CD3-CD56+ subsets found in RCC. Despite the many similar immunologic abnormalities in AA and RCC, the rate of autoimmune disease was significantly lower in childhood AA than RCC (p=0.008, χ2=6.976). The relative numbers of natural killer cells were significantly lower in RCC patients than AA patients. By month 6, there was no significant difference in autoimmune manifestations between RCC and AA in relation to the response to immunosuppressive therapy (p=0.907, χ2=0.014). The large overlap of analogous immunologic abnormalities indicates that RCC and childhood AA may share the same pathogenesis.

Classical pathway deficiencies - A short analytical review.

Deficiencies in the classical pathway of complement activation have some common features but show also great differences. Deficiencies of each of the components (C1q, C1s, C1r, C4 and C2) imply increased susceptibility to bacterial infections. They are also associated with increased risk to develop systemic lupus erythematosus where deficiency of C1q is strongly associated to the disease while C4 less and C2 much less. Deficiency of C1q affects only activation of the classical pathway while deficiency of C4 and C2 also prevent activation of the lectin pathway. Bypass mechanisms may result in complement activation also in absence of C2 but not in absence of C1q or C4. The genes for C2 and C4 isotypes are closely located within the MHC class III region on chromosome 6p and the genes for the 3 C1q chains are on chromosome 1p. Deficiencies of C1q and of C4 show genetic heterogeneity while deficiency of C2 in the great majority of cases is caused by a specific deletion. The production of C4 and C2 is mainly by the hepatocytes in the liver while C1q is produced by monocytic bone marrow derived cells. This has implications for the possibility to treat the deficiency and hematopoietic stem cell transplantation has been tried in C1q deficiency.

Clinical characteristics of IgA nephropathy associated with low complement 4 levels.

OBJECTIVE: C4 deficiency is the most commonly inherited immune disorder in human. The present study investigated the characteristics of the IgAN patients with low serum C4 levels. METHODS: We performed a prospective observational study. Clinical as well as histopathologic parameters were assessed. A Kaplan-Meier survival analysis was performed concerning the primary outcome defined as the serum creatinine increased 1.5-fold from baseline. The prognostic significances of clinical and histopathologic parameters were determined using Cox proportional hazards models. RESULTS: Five-hundred twelve biopsy proven IgAN cases were available for analysis with a median follow-up of 38.4 months. Ninety-nine cases (19.34%) presented with low C4 levels (LowC4 group) and the other 413 cases did not (NlowC4 group). At the time of renal biopsy, renal injury was lighter in the LowC4 group compared with the NlowC4 group. Renal C4 deposition was significantly decreased while IgM deposition was increased in the LowC4 group. A correlation analysis shows that lower C4 levels were associated with better renal presentations at biopsy. However, the risk of developing the primary outcome was significantly greater in those with low C4 levels. Specifically, during the follow-up period, the risk of developing primary outcome was nearly ten folds higher in those with low C4, compared to those without low C4. CONCLUSION: There is a high prevalence of low C4 levels in IgAN patients. These patients with low C4 levels exhibited better renal presentations at the time of renal biopsy, whereas might be associated with a poor prognosis.

Complement C4 deficiency--a plausible risk factor for non-tuberculous mycobacteria (NTM) infection in apparently immunocompetent patients.

BACKGROUND: Non-tuberculous mycobacteria (NTM) are ubiquitous in the environment and they infect mainly persons with underlying pulmonary diseases but also previously healthy elderly women. Defects in host resistance that lead to pulmonary infections by NTM are relatively unknown. A few genetic defects have been associated with both pulmonary and disseminated mycobacterial infections. Rare disseminated NTM infections have been associated with genetic defects in T-cell mediated immunity and in cytokine signaling in families. We investigated whether there was an association between NTM infections and deficiencies of complement components C4A or C4B that are encoded by major histocompatibility complex (MHC). METHODS: 50 adult patients with a positive NTM culture with symptoms and findings of a NTM disease were recruited. Patients' clinical history was collected and symptoms and clinical findings were categorized according to 2007 diagnostic criteria of The American Thoracic Society (ATS). To investigate the deficiencies of complement, C4A and C4B gene copy numbers and phenotype frequencies of the C4 allotypes were analyzed. Unselected, healthy, 149 Finnish adults were used as controls. RESULTS: NTM patients had more often C4 deficiencies (C4A or C4B) than controls (36/50 [72%] vs 83/149 [56%], OR = 2.05, 95%CI = 1.019-4.105, p = 0.042). C4 deficiencies for female NTM patients were more common than for controls (29/36 [81%] vs 55/100 [55%], OR = 3.39, 95% CI = 1.358-8.460, p = 0.007). C4 deficiences seemed not to be related to any specific underlying disease or C4 phenotype. CONCLUSIONS: C4 deficiency may be a risk factor for NTM infection in especially elderly female patients.

Common and specific associations of anti-SSA/Ro60 and anti-Ro52/TRIM21 antibodies in systemic lupus erythematosus.

Little information exists about the association of anti-SSA/Ro60 and anti-Ro52/TRIM21 with systemic lupus erytematosus (SLE) features. In this work, we analysed the associations of both anti-Ro reactivities with clinical and immunological manifestations in 141 SLE patients. Photosensitivity and xerophtalmia/xerostomia were found to be positively associated with both anti-SSA/Ro60 (P = 0.024 and P = 0.019, resp.) and anti-Ro52/TRIM21 (P = 0.026 and P = 0.022, resp.). In contrast, a negative association was detected regarding anti-phospholipid antibodies, anti-SSA/Ro60 having a stronger effect (P = 0.014) than anti-Ro52/TRIM21. Anti-SSA/Ro60 showed a specific positive association with hypocomplementemia (P = 0.041), mainly with low C4 levels (P = 0.008), whereas anti-Ro52/TRIM21 was found to be positively associated with Raynaud's phenomenon (P = 0.026) and cytopenia (P = 0.048) and negatively associated with anti-dsDNA (P = 0.013). Lymphocytes are involved in the relationship between anti-Ro52/TRIM21 and cytopenia since positive patients showed lower cell levels than negative patients (P = 0.036). In conclusion, anti-SSA/Ro60 and anti-Ro52/TRIM21 showed both common and specific associations in SLE. These data thus increase evidence of the different associations of the two anti-Ro specificities even in a particular disease.

Anaphylaxis followed by unilateral lung opacity and hypocomplementemia in a young female.

A 36-year-old woman was stung in the right wrist by a bee, suffered typical anaphylaxis, and was transferred to a local hospital. After a few hours, which corresponded to late-onset reaction, she developed shortness of breath and weakness and was transferred to the emergency department, where the diagnosis of anaphylaxis was confirmed. Serum complement levels, components C3 and C4, were undetectable. Flexible bronchoscopy excluded lung hemorrhage. She was on the ventilator for 4 days and was fully awake during that time. After the treatment, her improvement was rapid, and she fully recovered. Three weeks after she had been stung by a bee, skin prick tests to bee, wasp, and yellow jacket venom were done, and all tests came back negative as well as IgE and IgG4 antibodies to the same venoms. Coagulation factors and the complement, including C1q inhibitor, were normal. Occurrence of complement activation and consumption could point to the immune complexes as basis of pathophysiological mechanism. It remains unclear why such a reaction would involve only the right lung and why no detectable immune complexes were discovered. The clinical picture in the presented case resembled acute respiratory distress syndrome, but the exact nature of lung consolidation remains puzzling. The most likely explanation is a very rare case of airway obstruction. To our knowledge, this is the only reported case of anaphylaxis associated with undetectable serum complement levels. The potential role and diagnostic significance of hypocomplementemia in cases of anaphylaxis should be further investigated.

Cutaneous vasculitis and glomerulonephritis associated with C4 deficiency.

Complete deficiency of the fourth component of complement (C4) is an extremely rare condition. However, it has been reported that partial C4 deficiency can occur in normal subjects, and is associated with several immune diseases. We report a 44-year-old woman who developed slight oedema and punctate purpura on her lower legs after a common cold. She was noted to have persistent microscopic haematuria and proteinuria, and her C4 level was undetectable. On histological examination of a skin biopsy specimen, leucocytoclastic vasculitis was seen, with granular deposition of IgG, IgM, C3 and C1q on the vessel walls in the upper dermis. A renal biopsy showed mild mesangial proliferative glomerulonephritis with slight damage to the capillary loops, and granular deposits of IgM and C4 mainly in the mesangium. The patient was systemically well and needed no medication. The C4 level remained low during the observation period, but neither genotyping nor allotyping analysis identified a C4 deficiency.

Complement C4 maintains peripheral B-cell tolerance in a myeloid cell dependent manner.

The factors that allow self-reactive B cells to escape negative selection and become activated remain poorly defined. Using a BCR knock-in mouse strain, we identify a pathway by which B-cell selection to nucleolar self-antigens is complement dependent. Deficiency in complement component C4 led to a breakdown in the elimination of autoreactive B-cell clones at the transitional stage, characterized by a relative increase in their response to a range of stimuli, entrance into follicles, and a greater propensity to form self-reactive GCs. Using mixed BM chimeras, we found that the myeloid compartment was sufficient to restore negative selection in the autoreactive mice. A model is proposed in which in the absence of complement C4, inappropriate clearance of apoptotic debris promotes chronic activation of myeloid cells, allowing the maturation and activation of self-reactive B-cell clones leading to increased spontaneous formation of GCs.

Juvenile elastic arteries after 28 years of renal replacement therapy in a patient with complete complement C4 deficiency.

BACKGROUND: Complement activation products are present in atherosclerotic plaques. Recently, binding of complement to elastin and collagen in the aortic wall has been demonstrated, suggesting a role of complement in the development aortic stiffness and atherosclerosis. The definitive role of complement in atherosclerosis and arteriosclerosis, however, remains unclear. CASE PRESENTATION: We here describe a patient with hereditary complete deficiency of complement C4 suffering from Henoch-Schoenlein purpura and on renal replacement therapy for twenty-eight years. The patient had the full range of risk factors for vascular damage such as hypertension, volume overload, hyperphosphatemia and hyperparathyroidism. Despite that, his carotid artery intima media thickness was below the normal range and his pulse wave velocity was normal. In contrast, the patient's coronary and peripheral muscular arteries were heavily calcified. CONCLUSION: This case supports the hypothesis that complement plays an important role in the development of stiffness of elastic arteries. We speculate that inability to activate complement by the classical or lectin pathways protected the patient from atherosclerosis, arteriosclerosis, stiffening and calcification of the aorta and carotid arteries. Inhibition of complement activation may be a potential target for prophylactic and therapeutic interventions.

Impairment of CD4+CD25+ regulatory T cells in C4-deficient mice.

OBJECTIVE: To investigate the association between deficiencies of early components in the classical complement pathway and the development of SLE. METHODS: Forty inbred C57BL/6J mice and 40 knockout C4 complement gene (C4KO) mice, which included 10 mice in each age group (2, 4, 6, and 8 months) were used. The enumeration of CD4+CD25+ Tregs frequencies in bone marrow, spleen and peripheral blood from both normal and C4KO groups were performed by flow cytometry. The expression levels of Foxp3 and TGF-beta in the same tested tissues were measured using real time PCR. The antinuclear antibodies (ANA) were semi-quantitatively measured using ELISA. RESULTS: We report decreased frequencies of CD4+CD25+ Tregs and reduced expression levels of Foxp3 and TGF-beta, which efficiently program the development and function of Tregs, in lymphoid tissues and peripheral blood of C4KO mice. In this study, C4KO mice have higher titers of ANA than those of normal mice. Higher frequencies of mice positive for ANA are also found in older mice. CONCLUSIONS: The deficiency of the C4 gene induces the decreased numbers of Tregs that further increase the production of ANA resulting in the development of an autoimmune disorder. The outcomes of our study help us to understand the association between the deficiency of C4 in the classical complement pathway and development of autoimmune disorder via the role of Tregs.