Autoantibodies against aldehyde-modified collagen type IV are associated with risk of development of myocardial infarction

BACKGROUND

Oxidation of LDL particles entrapped in the extracellular matrix of the arterial wall is a key factor in the development of atherosclerosis. Lipid oxidation products, such as malondialdehyde (MDA), react with surrounding extracellular matrix proteins and cause modifications that are recognized by the immune system. MDA modification of collagen type IV is increased in carotid lesions from symptomatic patients and correlates with autoantibodies against MDA-modified collagen type IV in plasma.

OBJECTIVE

The aim of this study was to determine whether autoantibodies against MDA-modified collagen type IV predict risk of development of myocardial infarction (MI).

METHODS

Plasma levels of MDA-modified collagen type IV IgM and IgG antibodies were analysed by enzyme-linked immunosorbent assay in 385 subjects with incident MI during 13 years of follow-up and 410 age- and sex-matched controls in the Malmö Diet and Cancer study.

RESULTS

MDA-modified collagen type IV IgG levels were higher in cases with incident MI than in controls. Subjects in the highest tertile of MDA-modified collagen type IV IgG had an increased risk of MI (hazard ratio 1.56, 95% confidence interval 1.22-2.00, P for trend 0.0004). This association remained significant after adjusting for factors included in the Framingham risk score and diabetes. High levels of MDA-collagen type IV IgG were associated with increased carotid intima-media thickness and elevated plasma levels of matrix metalloproteinase 10 and 12.

CONCLUSIONS

Immune responses against MDA-modified collagen type IV are associated with more severe carotid disease and increased risk of MI. These immune responses may reflect LDL oxidation in the artery wall, but could also affect the atherosclerotic disease process.

Plasma stem cell factor levels are associated with risk of cardiovascular disease and death

OBJECTIVE

Stem cell factor (SCF) is a key growth factor for several types of stem and progenitor cells. There is experimental evidence that such cells are of importance for maintaining the integrity of the cardiovascular system. We investigated the association between circulating levels of SCF and risk for development of cardiovascular events and death.

METHODS

SCF was analysed by the proximity extension assay technique in plasma from 4742 subjects participating in the Malmö Diet and Cancer Study. Cardiovascular events and death were monitored through national registers with a mean follow-up time of 19.2 years.

RESULTS

Subjects with high baseline levels of SCF had lower cardiovascular (n = 340) and all-cause mortality (n = 1159) as well as a lower risk of heart failure (n = 177), stroke (n = 318) and myocardial infarction (n = 452). Smoking, diabetes and high alcohol consumption were associated with lower levels of SCF. Single nucleotide polymorphisms in the gene region encoding PDX1 C-terminal inhibiting factor 1 (PCIF1) and matrix metalloproteinase-9 were associated with plasma SCF levels. The highest SCF quartile remained independently associated with a lower risk of a lower risk of cardiovascular [hazard ratio and 95% confidence interval 0.59 (0.43-0.81)] and all-cause mortality [0.68 (0.57-0.81)], heart failure [0.50 (0.31-0.80)] and stroke [0.66 (0.47-0.92)], but not with MI [0.96 (0.72-1.27)] as compared with the lowest quartile when adjusting for traditional cardiovascular risk factors in Cox proportional hazard regression models.

CONCLUSIONS

This prospective population-based study demonstrates that subjects with high levels of SCF have a lower risk of cardiovascular events and death. The findings provide clinical support for a protective role of SCF in maintaining cardiovascular integrity.

Human Lipoproteins at Model Cell Membranes: Effect of Lipoprotein Class on Lipid Exchange

High and low density lipoproteins (HDL and LDL) are thought to play vital roles in the onset and development of atherosclerosis; the biggest killer in the western world. Key issues of initial lipoprotein (LP) interactions at cellular membranes need to be addressed including LP deposition and lipid exchange. Here we present a protocol for monitoring the in situ kinetics of lipoprotein deposition and lipid exchange/removal at model cellular membranes using the non-invasive, surface sensitive methods of neutron reflection and quartz crystal microbalance with dissipation. For neutron reflection, lipid exchange and lipid removal can be distinguished thanks to the combined use of hydrogenated and tail-deuterated lipids. Both HDL and LDL remove lipids from the bilayer and deposit hydrogenated material into the lipid bilayer, however, the extent of removal and exchange depends on LP type. These results support the notion of HDL acting as the ‘good’ cholesterol, removing lipid material from lipid-loaded cells, whereas LDL acts as the ‘bad’ cholesterol, depositing lipid material into the vascular wall.

Vaccination against T-cell epitopes of native ApoB100 reduces vascular inflammation and disease in a humanized mouse model of atherosclerosis

BACKGROUND AND OBJECTIVES

The T-cell response to low-density lipoprotein (LDL) in the vessel wall plays a critical role in atherosclerotic plaque formation and stability. In this study, we used a new translational approach to investigate epitopes from human apolipoprotein B100 (ApoB100), the protein component of LDL, which triggers T-cell activation. We also evaluated the potential of two selected native ApoB100 epitopes to modulate atherosclerosis in human ApoB100-transgenic Ldlr^-/- (HuBL) mice.

METHODS AND RESULTS

HuBL mice were immunized with human atherosclerotic plaque homogenate to boost cellular autoimmune response to tissue-derived ApoB100 epitopes. In vitro challenge of splenocytes from immunized mice with a library of overlapping native peptides covering human ApoB100 revealed several sequences eliciting T-cell proliferation. Of these sequences, peptide (P) 265 and P295 were predicted to bind several human leucocyte antigen (HLA) haplotypes and induced high levels of interferon (IFN)-γ. Vaccination of HuBL mice with these peptides mounted a strong adaptive immune response to native ApoB100, including high levels of epitope-specific plasma IgGs. Interestingly, P265 and P295 vaccines significantly decreased plaque size, reduced macrophage infiltration and increased IgG1 deposition in the plaques. Purified IgGs from vaccinated mice displayed anti-inflammatory properties against macrophages in vitro, reducing their response to LPS in a dose-dependent manner.

CONCLUSION

We identified two specific epitopes from human native ApoB100 that trigger T-cell activation and protect HuBL mice against atherosclerosis when used in a vaccine. Our data suggest that vaccination-induced protective mechanisms may be mediated at least in part through specific antibody responses to LDL that inhibit macrophage activation.

CD4+ CD56+ natural killer T-like cells secreting interferon-γ are associated with incident coronary events

BACKGROUND

CD3(+) CD56(+) natural killer T (NKT)-like cells are a subset of T cells characterized by expression of NK receptors and potent antitumour activity. It has also been suggested that they have a role in autoimmune disease, and levels of NKT-like cells are elevated in patients with coronary disease.

OBJECTIVES

To investigate whether high levels of CD3(+) CD56(+) NKT-like cells are associated with an increased incidence of cardiovascular disease and a lower incidence of cancer.

METHODS

This was a prospective study including 700 subjects participating in the baseline investigation of the Malmö Diet and Cancer study between 1991 and 1994. Leucocytes obtained at the baseline investigation and stored at -140 °C were thawed and CD3(+) CD56(+) cells analysed by flow cytometry. The incidence rates of cancer and coronary events during a mean follow-up of 15 years were determined through national registers.

RESULTS

Subjects in the lowest tertile of interferon (IFN)-γ-expressing CD4(+) CD56(+) cells were found to have an increased risk of incidence of coronary events (log-rank test: P < 0.05). This association remained significant after controlling for age, sex, smoking, body mass index, hypertension, diabetes and the Th1/Th2 and Th1/Treg cell ratios in a Cox proportional hazards regression model (hazard ratio 1.98, 95% confidence interval 1.24-3.16), but not when the LDL/HDL ratio was included in the model. There were no associations between CD3(+) CD56(+) NKT-like cells and incident cancer.

CONCLUSIONS

The present results could not confirm the hypothesis that low levels of CD3(+) CD56(+) NKT-like cells are associated with a higher incidence of cancer and a lower incidence of cardiovascular disease. However, we found that low levels of IFN-γ-expressing CD3(+) CD4(+) CD56(+) NKT-like cells were associated with an increased incidence of coronary events and that this association may be dependent on lipoproteins.

Association between CD8+ T-cell subsets and cardiovascular disease

BACKGROUND

The findings of experimental studies suggest that the immune system plays a key role in atherosclerosis, but the clinical importance of different immune cells in cardiovascular disease remains poorly characterized. In this study we investigated the association between CD8(+) T cells and carotid disease as well as development of cardiovascular disease events.

METHODS

The study cohort comprised 700 subjects from the cardiovascular arm of the Malmö Diet and Cancer Study. Peripheral blood mononuclear cells, obtained at the 1991-1994 baseline investigation and stored at -140 °C, were thawed and the different CD8(+) T-cell populations analysed by flow cytometry. Baseline carotid intima-media thickness and stenosis were assessed by ultrasonography and clinical events were monitored through validated national registers.

RESULTS

Subjects with a high fraction of CD8(+) T cells were characterized by decreased cytokine release from activated leucocytes, metabolic signs of insulin resistance and increased incidence of coronary events; hazard ratios (95% confidence intervals) for the second and third tertiles of CD8(+) T cells were 2.57 (1.16, 5.67) and 2.61 (1.19, 5,71), respectively, in a Cox proportional hazards regression model. Correlations were found between the fraction of CD8(+) CD25(+) T cells and the degree of carotid stenosis (r = 0.11, P < 0.01), and between the CD8(+) CD56(-) IFN-γ(+) T-cell fraction and the degree of stenosis (r = -0.18, P < 0.005). The association between CD8(+) CD56(-) IFN-γ(+) T cells and carotid stenosis remained significant after controlling for major cardiovascular disease risk factors.

CONCLUSION

This study provides prospective clinical evidence for a role of CD8(+) T cells in cardiovascular disease and suggests the existence of CD8(+) T-cell subsets with different pathological functions.

High levels of IgM against methylglyoxal-modified apolipoprotein B100 are associated with less coronary artery calcification in patients with type 2 diabetes

OBJECTIVE

  Advanced glycation end products (AGE) have been implicated in diabetic vascular complications through activation of pro-inflammatory genes. AGE-modified proteins are also targeted by the immune system resulting in the generation of AGE-specific autoantibodies, but the association of these immune responses with diabetic vasculopathy remains to be fully elucidated. The aim of this study was to determine whether antibodies against apolipoprotein B100 modified by methylglyoxal (MGO-apoB100) are associated with coronary atherosclerosis in patients with type 2 diabetes.

METHODS

  We measured antibodies against MGO-apoB100 in plasma from 497 type 2 diabetic patients without clinical signs of cardiovascular disease. Severity of coronary disease was assessed as coronary artery calcium (CAC) imaging. Immunoglobulin (Ig)M and IgG levels recognizing MGO-apoB100 were determined by enzyme-linked immunosorbent assay.

RESULTS

  Anti-MGO-apoB100 IgM antibody levels were higher in subjects with a low to moderate CAC score (≤400 Agatston units) than in subjects with a high score (>400 Agatston units; 136.8±4.4 vs. 101.6± 7.4 arbitrary units (AU), P<0.0001) and in subjects demonstrating no progression of CAC during 30 months of follow-up (136.4±5.7 vs. 113.9 ± 6.2 AU in subjects with progression, P<0.0001). Subjects with a family history of premature myocardial infarction had lower levels of anti-MGO-apoB100 IgM. Female subjects had higher levels of anti-MGO-apoB100 antibodies and lower CAC than men. Accordingly, high levels of IgM against MGO-apoB100 are associated with less severe and a lower risk of progression of coronary disease in subjects with type 2 diabetes.

CONCLUSIONS

Although conclusions regarding causal relationships based on epidemiological observations need to be made with caution, our findings suggest the possibility that anti-MGO-apoB100 IgM may be protective in diabetic vasculopathy.

Patients with irritable bowel syndrome and dysmotility express antibodies against gonadotropin-releasing hormone in serum

BACKGROUND

The etiology of irritable bowel syndrome (IBS) and dysmotility is in most cases unknown. Organic, pathognomonic changes have not been described. We have previously demonstrated sporadic expressions of antibodies against gonadotropin-releasing hormone (GnRH) in serum from these patients. The aim of this study was to screen for the presence of GnRH antibodies in healthy subjects and patients with gastrointestinal (GI) diseases.

METHODS

Consecutive patients suffering from either IBS, idiopathic dysmotility, GI complaints secondary to diabetes mellitus, celiac disease or inflammatory bowel disease (IBD) were included. Healthy blood donors served as controls. Blood samples were taken for analyzing IgM and IgG antibodies against GnRH using an ELISA method. Medical records were scrutinized with respect to duration of symptoms, co-existing diseases, drug treatments, hereditary factors, and laboratory analyses.

KEY RESULTS

Healthy controls expressed low levels of GnRH IgM antibodies in a prevalence of 23%. The prevalence of GnRH IgM antibodies in IBS and dysmotility patients was 42% (P = 0.008), and the levels were higher (P = 0.000). Patients with diabetes mellitus expressed GnRH IgM antibodies in the same prevalence as controls (25%), but in higher levels (P = 0.02). Patients with celiac disease or IBD had the same or lower levels of antibodies. There were no associations between antibodies, other co-existing diseases or laboratory analyses.

CONCLUSIONS & INFERENCES

Higher levels of GnRH IgM antibodies were detected in patients with IBS and dysmotility, but not organic GI diseases, compared with healthy controls. These findings suggest that IBS and dysmotility to some extent may be of an autoimmune origin.

Evidence for a role of regulatory T cells in mediating the atheroprotective effect of apolipoprotein B peptide vaccine

OBJECTIVES

Autoimmune responses against oxidized low-density lipoprotein are considered to play an important pro-inflammatory role in atherosclerosis and to promote disease progression. T-regulatory cells (Tregs) are immunosuppressive cells that have an important part in maintaining self-tolerance and protection against autoimmunity. We investigated whether aBp210, a prototype atherosclerosis vaccine based on a peptide sequence derived from apolipoprotein B, inhibits atherosclerosis through the activation of Tregs.

DESIGN

Six-week-old Apoe(-/-) mice were immunized with aBp210 and received booster immunizations 3 and 5 weeks later, as well as 1 week before being killed at 25 weeks of age.

RESULTS

At 12 weeks, immunized mice had increased expression of the Treg marker CD25 on circulating CD4 cells, and concanavalin A (Con A)-induced interferon-γ, interleukin (IL)-4, and IL-10 release from splenocytes was markedly depressed. At 25 weeks, there was a fivefold expansion of splenic CD4+ CD25+ Foxp3 Tregs, a 65% decrease in Con A-induced splenic T-cell proliferation and a 37% reduction in the development of atherosclerosis in immunized mice. Administration of blocking antibodies against CD25 neutralized aBp210-induced Treg activation as well as the reduction of atherosclerosis.

CONCLUSIONS

The present findings demonstrate that immunization of Apoe(-/-) mice with the apolipoprotein B peptide vaccine aBp210 is associated with activation of Tregs. Administration of antibodies against CD25 results in depletion of Tregs and blocking of the atheroprotective effect of the vaccine. Modulation in atherosclerosis-related autoimmunity by antigen-specific activation of Tregs represents a novel approach for treatment of atherosclerosis.

Weak associations between human leucocyte antigen genotype and acute myocardial infarction

OBJECTIVES

Human leucocyte antigens (HLAs) are polymorphic molecules involved in antigen presentation. Associations between HLA type and autoimmune diseases, such as type 1 diabetes and rheumatoid arthritis, are well established but the potential association of genetic variation affecting antigen presentation with cardiovascular disease has not been systematically investigated in large cohorts. The importance of such studies is stressed by recent experimental findings of an involvement of autoimmunity in the atherosclerotic disease process.

RESULTS

An SSP-PCR method was used for HLA genotyping to determine associations of HLA-DRB1, -DQA1 and -DQB1 with cardiovascular disease in a population-based cohort of 1188 acute myocardial infarction (AMI) patients and 1191 matched healthy controls. The HLA-DRB1*0101 allele, as well as the HLA-DRB1*0101-DQA1*01-DQB1*05 haplotype, was found to be associated with increased risk for AMI (OR 1.24; 95% CI 1.00-1.54 for both). In contrast, the DRB1*07 and DQA*02 alleles (OR 0.78; 95% CI 0.65-0.95 for both), as well as the DRB1*07-DQA*02-DQB*02 haplotype, conferred protection (OR 0.79; 95% CI 0.63-0.98). An HLA risk score taking each individual's both haplotypes into account was higher amongst cases (2.43 +/- 0.92 vs. 2.29 +/- 0.95, P = 0.001). The association between HLA risk score and AMI was independent of other cardiovascular risk factors assessed.

CONCLUSIONS

This study demonstrates that the associations between HLA-DRB1 and DQA1 loci and cardiovascular disease exists but that they are considerably weaker than those previously reported for other diseases with an established autoimmune aetiology such as type 1 diabetes, systemic lupus erythematosus and rheumatoid arthritis.

Vaccines modulating lipoprotein autoimmunity as a possible future therapy for cardiovascular disease

Current strategies for prevention of cardiovascular disease focus on risk factor intervention. Although these have been proven both safe and effective results from randomized clinical trials suggest that it is difficult to achieve relative risk reductions exceeding 40% with this approach. To further improve efficacy future therapies must aim at targeting the actual disease process in the arterial wall. Emerging evidence have identified an important role of the immune system in atherosclerosis and suggest that modulation of autoimmune responses against oxidized LDL and other antigens in the atherosclerotic plaque represent one possible new approach to disease prevention. Oxidized LDL is targeted by both antibody-mediated and cellular immune responses and as much as 10% of the T cells in atherosclerotic plaques are oxidized LDL-specific. Immune activation in the atherosclerotic plaque is primarily of the pro-inflammatory Th1-type and inhibition Th1 immunity reduces atherosclerosis in experimental animals. Atherosclerosis vaccines based on antigens derived from LDL have been developed to modulate these processes. Their mechanisms of action remain to be full characterized but may involve expression of protective antibodies that facilitate the removal of oxidized LDL and antigen-specific regulatory T cells that counteract Th1 autoimmunity against oxidized LDL. In this review we will discuss the possibilities and challenges encountering the translation of immune-modulatory therapy for atherosclerosis from the experimental stage into the clinic.

Associations between autoantibodies against apolipoprotein B-100 peptides and vascular complications in patients with type 2 diabetes

AIMS/HYPOTHESIS

Oxidation of LDL in the arterial extracellular matrix is a key event in the development of atherosclerosis and autoantibodies against oxidised LDL antigens reflect disease severity and the risk of developing acute cardiovascular events. Since type 2 diabetes is associated with increased oxidative stress, we tested the hypothesis that autoantibodies against oxidised LDL antigens are biomarkers for vascular complications in diabetes.

METHODS

We studied 497 patients with type 2 diabetes without clinical signs of coronary heart disease. Oxidised LDL autoantibodies were determined by ELISA detecting IgG and IgM specific for native and malondialdehyde (MDA)-modified apolipoprotein B-100 peptides p45 and p210. The severity of coronary disease was assessed as the coronary artery calcium score.

RESULTS

Patients affected by retinopathy had significantly higher levels of IgG against MDA-p45 and MDA-p210. In contrast, high levels of autoantibodies against the corresponding native peptides were associated with less coronary calcification and a lower risk of progression of coronary disease.

CONCLUSIONS/INTERPRETATION

Our observations suggest that LDL oxidation is involved in the pathogenesis of diabetic retinopathy and that autoantibodies against apolipoprotein B peptides may act as biomarkers for both micro- and macrovascular complications in diabetes.

Immune responses against fibronectin modified by lipoprotein oxidation and their association with cardiovascular disease

OBJECTIVES

Accumulation and subsequent oxidation of LDL in the arterial wall are considered as key events in the development of atherosclerosis. We have investigated the possibility that LDL oxidation results in release of aldehydes that modify surrounding matrix proteins and that this may target immune responses against the plaque extracellular matrix and modulate the disease progression.

RESULTS

Using custom-made ELISAs we demonstrate that human plasma contains autoantibodies against aldehyde-modified fibronectin (FN) and to a lesser extent also other extracellular matrix proteins including collagen type I, type III, and tenascin-C. Immunohistochemistry and western blot analysis showed that aldehyde-modified FN is present in human atherosclerotic plaques and that aldehydes generated by oxidation of LDL formed adducts with FN in vitro. We also demonstrate that aldehyde-modification of FN results in a loss of its ability to promote basal secretion of cytokines and growth factors from cultured macrophages without affecting the ability of the cells to respond to stimulation with LPS. A prospective clinical study demonstrated that subjects that subsequently developed acute myocardial infarction or sudden cardiac death had lower baseline levels of autoantibodies against aldehyde-modified FN than matched controls.

CONCLUSIONS

These observations demonstrate that oxidation of LDL in the arterial wall may lead to aldehyde-modification of surrounding extracellular matrix proteins and that these modifications may affect macrophage function and activate autoimmune responses of pathophysiological importance for the development of atherosclerosis.

Treatment with apo B peptide vaccines inhibits atherosclerosis in human apo B-100 transgenic mice without inducing an increase in peptide-specific antibodies

OBJECTIVES

Autoantibodies to apolipoprotein (apo) B-100 peptides are present in human plasma and have been shown to be associated with decreased cardiovascular risk. The present study aimed to determine if apo B-100 peptide vaccines are atheroprotective in mice expressing human apo B-100 and if the effectiveness of the vaccines is influenced by the level of pre-existing peptide-specific autoantibodies.

DESIGN

LDL receptor(-/-)/human apo B-100 transgenic mice were immunized with native human apo B-100 peptides p45 or p210 at 6, 9 and 11 weeks and the extent of atherosclerosis determined by en face Oil Red O staining of the aorta at 25 weeks. Autoantibody levels were determined by enzyme-linked immunosorbent assay, and RNA expression in the spleen was assessed by real time PCR.

RESULTS

Control mice had high levels of autoantibodies against p210 but only low levels against p45. Immunization with native p45 and p210 reduced atherosclerosis by 66% (P < 0.02) and 59% (P = 0.06), respectively. The atheroprotective effect of apo B peptide immunization occurred in the absence of an increase in peptide-specific IgG, but was associated with an increase in IgM recognizing native and copper-oxidized LDL.

CONCLUSIONS

Immunization with apo B peptide-based vaccines inhibits atherosclerosis in mice expressing human apo B-100 suggesting that they can interact with their target as expressed in humans. The protective effect is independent of the pre-existing level of apo B peptide autoantibodies and can occur without activating an increase in peptide-specific antibodies suggesting that atheroprotection can be mediated by cellular immune responses.

Increased rate of apoptosis in intimal arterial smooth muscle cells through endogenous activation of TNF receptors

Intimal proliferation of smooth muscle cells (SMCs) is a key event in the vascular response to injury, including the early stages of atherosclerosis and restenosis after angioplasty. Tumor necrosis factor-alpha (TNF-alpha) has been reported to stimulate growth of cultured human SMCs, but activation of TNF receptors is also known to induce cell death by apoptosis. We report here that SMCs isolated from the neointima of injured rat aortas are characterized by increased expression of TNF-alpha in response to interleukin-1beta and gamma-interferon compared with medial SMCs. Basal and serum-stimulated DNA synthesis was higher in intimal than in medial SMCs. In contrast to previous findings on human SMCs, exposure to interleukin-1beta/gamma-interferon or TNF-alpha did not affect the growth of rat medial SMCs, inhibited DNA synthesis, and decreased cell numbers in cultures of intimal SMCs. Incubation of intimal SMCs with these cytokines also resulted in induction of terminal dUTP nick end-labeling positivity and caspase-3 expression, suggesting cell death by apoptosis, whereas medial cells were markedly less sensitive in this respect. Cytokine-induced apoptosis in intimal cells was effectively inhibited by treatment with antibodies against TNF receptors. These findings suggest that endogenous activation of TNF receptors may represent a way to limit accumulation of SMCs in injured arteries. This mechanism may also be important in SMC death in advanced atherosclerotic plaques.

Accumulation of LDL in rat arteries is associated with activation of tumor necrosis factor-alpha expression

Activation of vascular inflammation in response to hyperlipidemia is believed to play an important role during the early stages of atherogenesis. We demonstrate here that exposure of cultured, rat aortic smooth muscle cells to low density lipoprotein (LDL) stimulated tumor necrosis factor-alpha (TNF-alpha) mRNA and protein expression. Oxidative modification of LDL resulted in a reduction of this stimulatory effect. To analyze whether a similar response also occurs in vivo, we used a recently developed model in which the effects of a rapid accumulation of human LDL in rat arteries can be studied. As previously reported, epitopes specific for human apolipoprotein B began to accumulate in the aorta within 2 to 6 hours after injection of 6 mg of human LDL. This was followed by expression of oxidized LDL-specific epitopes after 12 hours. There was no vascular expression of TNF-alpha at baseline or in phosphate-buffered saline-injected control rats. However, 24 hours after injection of native LDL, there was a marked induction of TNF-alpha mRNA and immunoreactivity in the aorta and other large arteries, whereas injection of oxidized LDL was without effect in this respect. Preincubation of LDL with the antioxidant probucol before injection markedly decreased the expression of TNF-alpha immunoreactivity. The present findings support the notion that LDL may activate arterial expression of TNF-alpha and suggest 1 possible mechanism for the inflammatory response in the early stages of atherosclerosis. The role of LDL oxidation in this process remains to be fully elucidated.

Properdin deficiency in a large Swiss family: identification of a stop codon in the properdin gene, and association of meningococcal disease with lack of the IgG2 allotype marker G2m(n)

Properdin deficiency was demonstrated in three generations of a large Swiss family. The concentration of circulating properdin in affected males was < 0.1 mg/l, indicating properdin deficiency type I. Two of the nine properdin-deficient males in the family had survived meningitis caused by Neisseria meningitidis serogroup B without sequel. Two point mutations were identified when the properdin gene in one of the properdin-deficient individuals was investigated by direct solid-phase sequencing of overlapping polymerase chain reaction (PCR) products. The critical mutation was found at base 2061 in exon 4, where the change of cytosine to thymine had generated the stop codon TGA. The other mutation was positioned at base 827 in intron 3. The stop codon in exon 4 was also demonstrated by standard dideoxy sequencing in three additional family members. The question was asked if genetic factors such as partial C4 deficiency and IgG allotypes could have influenced susceptibility to meningococcal disease in the family. No relationship was found between C4 phenotypes and infection. Interestingly, the two properdin-deficient males with meningitis differed from the other properdin-deficient persons in that they lacked the G2m(n) allotype, a marker known to be associated with poor antibody responses to T-independent antigens. This implies that the consequences of properdin deficiency might partly be determined by independent factors influencing the immune response.

Characterization of non-expressed C4 genes in a case of complete C4 deficiency: identification of a novel point mutation leading to a premature stop codon

The genetic basis of complete C4 deficiency in a patient with SLE was investigated. Previous studies have demonstrated that this patient has two different major histocompatibility complex (MHC) haplotypes that each contain a major deletion and a non-expressed C4 gene. In the present study, non-expression of the C4 genes was explained by the finding of two distinct C4 gene mutations. A previously described two base pair insertion in exon 29 of the C4 gene was detected in the paternal MHC haplotype [HLA-A2, B40, SC00, DR6]. The maternal haplotype [HLA-A30, B18, F1C00, DR3] carried a C4 gene with a one base pair deletion in exon 20 generating a premature stop codon. This mutation was neither found in 10 individuals with known non-expressed C4 genes nor in 9 individuals homozygous for the complotype F1C30. The isotype and allotype specific regions of the patient's C4 genes were sequenced, and both contained C4A3a sequence. In conclusion, two different MHC haplotypes resembling the extended haplotypes [HLA-A2, B40, SC02, DR6] and [HLA-A30, B18, F1C30, DR3] both contained a non-expressed C4A gene that was due to either of two distinct mutations, demonstrating the heterogeneous genetic background of C4 deficiency.

Expression of properdin in complete and incomplete deficiency: normal in vitro synthesis by monocytes in two cases with properdin deficiency type II due to distinct mutations

Three properdin deficiency phenotypes have been reported--complete deficiency (type I), incomplete deficiency (type II), and dysfunction of properdin protein (type III)--all associated with increased susceptibility to meningococcal disease. Expression of properdin by monocytes was examined in type I deficiency and in two unrelated cases with type II deficiency, one from a Swedish and one from a Danish family. The properdin gene in the Danish family contained a point mutation in exon 8 causing a Gln316-->Arg substitution, distinct from a point mutation in exon 4 previously found in the Swedish family. Both genes coded for physicochemically abnormal properdin molecules with changed hydrophilicity. Monocytes from all the properdin-deficient individuals produced properdin mRNA in a normal fashion. In type I deficiency no intracellular or secreted properdin was found, indicating rapid intracellular degradation. Monocytes from the males with type II deficiency expressed and secreted properdin normally. Properdin in sera with type II deficiency showed abnormal oligomerization with a relative decrease in properdin trimers and tetramers. Our findings suggest that the low concentration of circulating properdin in type II deficiency is caused by increased extracellular catabolism. Analysis of properdin expression by monocytes in a female carrier in the family with properdin deficiency type I provided direct evidence of lyonization at the cellular level.

Molecular characterization of properdin deficiency type III: dysfunction produced by a single point mutation in exon 9 of the structural gene causing a tyrosine to aspartic acid interchange

Inherited properdin deficiency is an X-linked recessive disorder clinically manifested by susceptibility to meningococcal disease. Deficiency of properdin is characterized by complete absence (type I), very low level presence (type II), or the presence of a dysfunctional properdin protein in serum as found in one Dutch family (type III). To better understand the dysfunctional protein on the molecular level, samples from three members of the Dutch family were analyzed by direct genomic sequencing. The sequence of the complete gene, including 10 exons and 9 introns, covering about 6500 bases was determined. The dysfunctional properdin was found to be caused by a single T to G mutation in exon 9, which gives rise to a substitution of a tyrosine by an aspartic acid residue at position 387. This change to a hydrophilic amino acid affects the function of the properdin molecule, although the oligomerization of dysfunctional properdin molecules was similar to that of normal properdin. In binding studies with C3b and properdin in serum, no properdin deposition was detected with the type III deficient serum. Inhibition studies with different decapeptides revealed distinct inhibitory sequences, and indicated also that the part of properdin containing the type III mutation was not directly involved in the binding to C3b. The mutation most likely causes conformational changes that make the properdin molecule dysfunctional by affecting its binding to C3b.

Molecular characterization of properdin deficiency type III: dysfunction produced by a single point mutation in exon 9 of the structural gene causing a tyrosine to aspartic acid interchange

Inherited properdin deficiency is an X-linked recessive disorder clinically manifested by susceptibility to meningococcal disease. Deficiency of properdin is characterized by complete absence (type I), very low level presence (type II), or the presence of a dysfunctional properdin protein in serum as found in one Dutch family (type III). To better understand the dysfunctional protein on the molecular level, samples from three members of the Dutch family were analyzed by direct genomic sequencing. The sequence of the complete gene, including 10 exons and 9 introns, covering about 6500 bases was determined. The dysfunctional properdin was found to be caused by a single T to G mutation in exon 9, which gives rise to a substitution of a tyrosine by an aspartic acid residue at position 387. This change to a hydrophilic amino acid affects the function of the properdin molecule, although the oligomerization of dysfunctional properdin molecules was similar to that of normal properdin. In binding studies with C3b and properdin in serum, no properdin deposition was detected with the type III deficient serum. Inhibition studies with different decapeptides revealed distinct inhibitory sequences, and indicated also that the part of properdin containing the type III mutation was not directly involved in the binding to C3b. The mutation most likely causes conformational changes that make the properdin molecule dysfunctional by affecting its binding to C3b.

Sequence-based analysis of properdin deficiency: identification of point mutations in two phenotypic forms of an X-linked immunodeficiency

Properdin deficiency is an inherited X-linked disorder causing increased susceptibility to meningococcal disease. Here, underlying genetic defects in the properdin gene were identified for the first time. Samples from individuals with type I deficiency, defined as complete absence of properdin in serum, and individuals with type II deficiency, characterized by low concentrations of properdin in serum, were analyzed by direct chromosome sequencing of overlapping PCR products. The complete gene, including 10 exons and 9 introns, covering 6460 bases of the region Xp11, was investigated by direct solid-phase sequencing. In the related individuals with type I deficiency a C to T mutation in exon 5 was identified, which gives rise to a stop codon TGA and thus a truncated gene product. In addition, point mutations were found in 4 introns and a silent mutation in exon 10. In the properdin gene from related individuals with type II deficiency two point mutations were found, one in intron 3 and one in exon 4. The latter mutation yields a substitution of arginine to tryptophan, which may affect folding, secretion, and/or turnover of the protein. The genetic and biochemical implications of these mutations are discussed.

New procedure for the detection of complement deficiency by ELISA. Analysis of activation pathways and circumvention of rheumatoid factor influence

A procedure using enzyme-linked immunosorbent assays for the assessment of complement function has been evaluated. The sera investigated were incubated in microtiter plates with solid-phase complement activators. Human polyclonal IgG or monoclonal IgM were used for classical activation pathway assays and Salmonella typhosa lipopolysaccharide (LPS) for alternative activation pathway assays. The analysis focussed on deposition of C9 and properdin as detected with enzyme-conjugated antibodies. In an attempt to avoid spurious results due to rheumatoid factors in patient sera, monoclonal mouse and chicken antibodies were unsuccessfully tested as indicator reagents in the assay with solid-phase IgG. However, the use of solid-phase IgM as an activator completely circumvented the influence of rheumatoid factors. With solid-phase IgG or IgM, properdin deposition occurred in the absence of factor D. A combination of assays is suggested for diagnostic purposes: IgM-coated plates with detection of bound C9 and properdin for the classical pathway and LPS-coated plates with detection of bound properdin for the alternative pathway. The procedure distinguished between defects of the classical activation pathway (C1, C4, C2), the alternative activation pathway (C3, factor B, factor D, properdin) and the terminal components (C5-C9). This analytical approach may be useful for detection of inherited complement deficiency and the assessment of complement function in acquired complement deficiency states.