Autoantibodies to the Atheroma Component Beta2-Glycoprotein I and Risk of Symptomatic Peripheral Artery Disease

Peripheral artery disease (PAD) is mostly related to atherosclerosis. Autoimmunity and, in particular, antibodies to cardiolipin (aCL) and phospholipid cofactors such as beta2-glycoprotein I (beta2-gpI) might influence the development of atheroma. Beta2-glycoprotein I (beta2-gpI) has been found in atheroma. It has previously been shown that immunoglobulin A (IgA) anti-beta2-gpI antibodies are associated with a risk of cerebral ischemia and myocardial infarction. This case control study aimed to determine whether elevated levels of aCL/anti-beta2-gpI antibodies are associated with a risk of symptomatic PAD (sPAD). Cases comprised a nonselected population of patients with sPAD (intermittent claudication or critical ischemia). Patient recruitment was based on arteriography changes. Controls were selected from patients admitted to orthopedic wards as a result of fractures or muscle-ligamentous disorders. Age, sex, race, hypertension, smoking, diabetes mellitus, and hypercholesterolemia were evaluated as risk factors in both groups. IgG/IgM/IgA aCL and anti-beta2-gpI were detected by enzyme-linked immunoabsorbant assays (ELISA). To estimate the grade of association of antibodies with sPAD, odds ratios (OR) were calculated. Logistic regression was utilized for adjustment of confounding factors. Seventy-seven cases and 93 controls were studied. The mean age was 61.5 years for cases and 47.5 years for controls (p <0.001). Among the risk factors evaluated, the presence of hypertension showed the strongest association with sPAD (OR 12.1; 95%CI 5.8—30). The presence of IgA anti-beta2-gpI was independently associated with sPAD (OR 5.4; 95%CI 1.8—15.8; p = 0.01). IgA aCL was strongly associated with the outcome (nonadjusted OR 11.5 after Agresti correction). IgA aCL and IgA anti-beta2-gpI antibodies were not associated with any known risk factors for sPAD or with arteriography changes. The occurrence of these autoantibodies might represent one of the links between autoimmunity and atherosclerosis in patients with sPAD.

Anti-beta2-glycoprotein I autoantibodies and metabolic syndrome

BACKGROUND

The metabolic syndrome (MetS) is a proatherogenic entity. Autoantibodies to phospholipid cofactors such as beta2-glycoprotein I (beta2-gpI) can influence atheroma appearance. Previous studies confirmed an association of IgA anti-beta2-gpI antibodies with cerebral ischemia, myocardial infarction, peripheral artery disease and carotid disease.

OBJECTIVE

This case-control study evaluates a possible association of anti-beta2-gpI and anticardiolipin (aCL) antibodies with non-complicated MetS.

METHODS

Cases comprised patients with MetS without history of vascular events; controls included individuals from the Orthopedic Infirmary admitted due to musculoskeletal disorders. Age, sex, race, history of hypertension, smoking, hypercholesterolemia and diabetes mellitus were evaluated as risk factors in both groups. IgG, IgM, and IgA anti-beta2-gpI and aCL antibodies were detected by enzymatic immunoassay.

RESULTS

Sixty-eight patients with MetS and 82 controls were studied. Patients with MetS showed mean age higher than controls (P = 0.001), while males (P = 0.003; OR 0.31; 95%CI 0.15-0.16) and Caucasian ethnicity (P = 0.004; OR 0.25; 95%CI 0.10-0.60) predominated in controls. History of hypertension, hypercholesterolemia and diabetes mellitus were more prevalent in cases than in controls (P < 0.05). The frequency of aCL antibodies (all isotypes) and of IgG and IgM anti-beta2 gpI did not significantly differ in cases and controls. IgA anti-beta2-gpI antibodies were significantly more frequent in MetS patients (42.2%) than controls (10.9%) (P < 0.001). The adjusted OR for IgA anti-beta2-gpI antibodies was 3.60 (95%CI 1.55-8.37; P = 0.003).

CONCLUSION

The current study shows that elevated levels of IgA autoantibodies to β2-gpI might be independently associated to MetS.

IgA antibodies to Chlamydia trachomatis and metabolic syndrome

Chlamydia pneumoniae may trigger atherogenesis. Chlamydia trachomatis (CT) can also induce endothelial activation. However, its role in metabolic syndrome (METS), a proatherogenic entity, has remained unexplored. In this study the frequencies of IgA and IgG anti-CT antibodies were evaluated by immunoenzymatic assay in METS patients and healthy controls. The survey included 238 individuals (148 with METS). The mean age was 59.7 years. IgA anti-CT antibodies were found significantly more frequently in METS patients (16.9%) than in controls (5.6%) (P= 0.015). The role of such IgA response in METS should be further investigated.

Anti-CCP antibodies have more diagnostic impact than rheumatoid factor (RF) in a population tested for RF

To compare the diagnostic powers of rheumatoid factor (RF) and anti-cyclic citrullinated peptide (CCP) in a population selected for its high statistical relevance, over a 6-month period, an informed consent to test for anti-CCP was obtained from 1,025 consecutive patients for whom RF was ordered at a University laboratory. Within 1 year, a diagnosis was obtained without informing the physician about the anti-CCP result. Extensive statistical analyses were performed. A total of 768 patients satisfied the inclusion criteria, and 132 were classified as having RA, yielding a pre-test probability of RA of 17%. The sensitivities for anti-CCP and RF were 62 and 64% (P = 0.83), and the specificities were 97 and 90% (P < 0.001), respectively. The positive predictive value (PPV) was 79% for anti-CCP and 56% for RF (P < 0.001), whereas the negative predictive value was 92% for both. The likelihood ratio (LR) was 17.9 for anti-CCP and 6.2 for RF (P < 0.005). Forty RA patients were diagnosed with RA of less than 2 years length, and the same significant statistic differences between anti-CCP and RF were observed. Placing the results of both tests together, or using different cutoff points, increased the diagnostic utility of the tests. The anti-CCP test has statistically shown significant higher specificity, PPV, and LR for RA than the RF test in a clinically diverse population. If new criteria are to be devised to help diagnose early RA, anti-CCP should be included because it has a greater diagnostic impact than RF.

Patients with atherosclerotic syndrome, negative in anti-cardiolipin assays, make IgA autoantibodies that preferentially target domain 4 of β2-GPI

Autoantibodies targeting beta2-glycoprotein l (beta2-GPI), a component of the atherosclerotic plaque, are commonly found in patients with acute ischemic syndromes. Serum samples from APS (antiphospholipid syndrome) patients and from cardiovascular patients exhibiting acute atherosclerotic syndromes were analyzed for IgG and IgA antibodies in both anti-beta2-GPI and anticardiolipin (aCL) ELISA assays. All of the APS samples used here were positive in both assays. Serum samples from 382 atherosclerosis patients were also analyzed for IgG and IgA antibodies in the same assays. In sharp contrast to the APS samples, we found that only 1% of the samples from atherosclerosis patients were positive for IgA aCL, and 1.6% positive for IgG aCL, whereas 35.6% were positive for IgA anti-beta2-GPI and only 1.6% for IgG anti-beta2-GPI. The antigenic specificity of 29 serum samples from atherosclerosis patients was evaluated. Six different recombinant domain-deleted mutants (DM) of human beta2-GPI and full-length human beta2-GPI (wild-type) were used in competitive inhibition assays to inhibit the autoantibodies from binding in the anti-beta2-GPI ELISA assays. Domain-deleted mutants D--345 and D--45 inhibited the binding in the IgA anti-beta2-GPI assay, suggesting that these autoantibodies recognize domain 4 of the beta2-GPI molecule. These results clearly show that IgA anti-beta2-GPI autoantibodies from atherosclerotic patients are distinct from IgA autoantibodies found in APS samples.

Autoantibodies to the nucleolar organizer antigen NOR-90 in children with systemic rheumatic diseases

OBJECTIVE

To determine the frequency of autoantibodies directed against the nucleolar organizer antigen NOR-90 [human upstream binding factor (hUBF)] in pediatric patients with systemic rheumatic diseases. Two children with antibodies to NOR-90 are reported.

METHODS

Two hundred thirty-eight sera from children with systemic rheumatic diseases were screened for autoantibodies directed against hUBF by indirect immunofluorescence and immunoblotting using MOLT-4 cell extracts. Reactivity with hUBF was confirmed by immunoprecipitation of the recombinant hUBF protein.

RESULTS

Two sera out of 238 (< 1.0%) with reactivity against hUBF were identified. One patient had recurrent abdominal pain, headache, and Raynaud's phenomenon. There has been no evidence of an active systemic rheumatic disease in more than 8 years of followup. The 2nd patient had Raynaud's phenomenon and systemic lupus erythematosus.

CONCLUSION

Antibodies to hUBF are rare in children with systemic rheumatic diseases. Raynaud's phenomenon was a clinical feature common to both patients.

Antiphospholipid antibodies and HLA associations in primary Sjögren's syndrome

Blood samples from 65 patients with primary Sjögren's syndrome were evaluated for the presence of antiphospholipid antibodies. Increased levels of antiphospholipid antibodies were found in 13 of 65 (20%) of patients. These antiphospholipid antibodies were predominantly of the IgA isotype, in contrast with the IgG isotype antiphospholipid antibodies found in patients with systemic lupus erythematosus (SLE). The presence of IgA antiphospholipid antibodies in the patients with primary Sjögren's syndrome was not significantly associated with arterial or vascular thrombosis, nor peripheral or central nervous system vasculitis. There was no association with laboratory determined features such as lupus anticoagulant or false positive results of the Venereal Disease Research Laboratory (VDRL) test. Oligonucleotide specific DNA amplification and hybridisation with allele specific probes was used to examine the HLA-D antigens occurring in this group of patients with primary Sjögren's syndrome. Of 13 patients with antiphospholipid antibodies, seven had the genotype HLA-DR2/DR3. However, compared with the whole group of 65 patients with Sjögren's syndrome, no increased occurrence of haplotype DR2 or DR3 was noted. These results suggest that gene interaction between DR2 and DR3 may play a part in the production of antiphospholipid antibodies in patients with Sjögren's syndrome. In contrast with patients with SLE, the IgA antiphospholipid antibodies in patients with Sjögren's syndrome are not risk factors for thrombosis or vasculitis. The presence of IgA antiphospholipid antibodies in patients with Sjögren's syndrome probably reflects its production at mucosal sites of inflammation and the absence of vasculopathy may be due to the inability of IgA antibodies to activate complement.

Antibody to phosphatidylethanolamine in a patient with lupus anticoagulant and thrombosis

Most patients with lupus anticoagulant (LA) activity have coincident antibodies to a group of negatively charged phospholipids, and its is suggested that LA and anticardiolipin tests detect antibodies with overlapping specificities. Some discordance between the two assays has been described, however. One patient presenting with severe thrombotic disease (recurrent deep vein thrombosis, pulmonary embolism, inferior venocaval obstruction, myocardial infarction, and digital gangrene) showed strong LA activity in February 1987. An enzyme linked immunosorbent assay (ELISA) showed no binding to the negatively charged phospholipids cardiolipin, phosphatidylserine, and phosphatidic acid, but binding to zwitterionic phosphatidylethanolamine (PE) was demonstrated. Inhibition studies and affinity purification confirmed this finding. Interestingly, the serum did not bind to the kaolin cephalin clotting time reagent when used as antigen in an ELISA. The pathogenic significance of anti-PE antibodies and their relation to LA remains to be clarified. Further studies of the occurrence of anti-PE antibodies in patients with LA activity who have negative anticardiolipin tests are suggested.