Specificity of anti-phospholipid antibodies in infectious mononucleosis: a role for anti-cofactor protein antibodies.
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The antigen specificity of anti-phospholipid antibodies in infectious mononucleosis (IM) was studied using ELISA for the detection of anti-beta2-glycoprotein I (beta2-GPI), anti-annexin V, anti-protein S and anti-prothrombin antibodies and TLC immunostaining for the detection of anti-phospholipid antibodies. This technique enabled us to look at antibodies reacting to 'pure' phospholipid antigens in the absence of protein contamination. Sera from 46 patients with IM, 18 with systemic lupus erythematosus (SLE), 21 with primary anti-phospholipid antibody syndrome (PAPS), 50 with Helicobacter pylori infection and 30 healthy blood donors were tested. This study highlights anti-phospholipid antibodies in patients with IM as specific 'pure' anti-cardiolipin antibodies, while in PAPS and SLE patients anti-phosphatidylserine and anti-phosphatidylethanolamine antibodies were also found. This investigation also shows that the anti-cardiolipin antibodies found in IM can be present with anti-cofactor protein antibodies. The higher prevalence of anti-cofactor antibodies found in IM sera than in Helicobacter pylori sera may be due to the immunostimulatory effect and/or the polyclonal activation often observed in course of Epstein-Barr virus infection. However, anti-beta2-GPI and, to a lesser extent, anti-prothrombin antibodies occur with a significantly lower prevalence in IM than in PAPS patients. This finding suggests that these antibodies should be regarded as the expression of the broad autoimmune syndrome involving the phospholipid-binding plasma proteins. (+info)
Frequent reversible membrane damage in peripheral blood B cells in human T cell lymphotropic virus type I (HTLV-I)-associated myelopathy/tropical spastic paraparesis (HAM/TSP).
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Apoptosis in peripheral blood lymphocyte populations in HTLV-I-infected people in vivo was examined, to study the lymphocyte dynamics in HTLV-I infection. Freshly isolated lymphocytes from 10 non-infected healthy people, eight asymptomatic HTLV-I carriers and 15 patients with HAM/TSP were stained with FITC-labelled annexin V to detect phosphatidylserine (PS) residue exposure at the outer plasma membrane leaflet as an early marker of apoptosis. There was no significant difference in annexin V positivity in CD4+ and CD8+ lymphocytes between non-infected subjects, asymptomatic carriers and HAM/TSP patients, but there was a greatly increased exposure of PS on CD19+ lymphocytes (B cells) detected by FITC-annexin V in 12 out of 15 (80%) HAM/TSP patients, while only two out of eight (25%) asymptomatic carriers and none of the non-infected healthy people showed this aberrant PS exposure on B cells. The intensity of annexin V staining of B cells in HAM/TSP was intermediate, as distinct from the high annexin V staining on advanced apoptotic cells. However, annexin V positivity was decreased when the cells were stained after 24 h of culture, suggesting that the intermediate PS exposure on the B cell in HAM/TSP is not a consequence of an apoptotic process, but rather reflects reversible membrane damage. B cells with PS exposure in vivo might provide a site for coagulation and inflammation, and so contribute to the pathogenesis of HAM/TSP and its complications. (+info)
Membrane-induced conformational change in human apolipoprotein H.
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The interaction of apolipoprotein H (Apo H) with lipid membrane has been considered to be a basic mechanism for the biological function of the protein. Previous reports have demonstrated that Apo H can interact only with membranes containing anionic phospholipids. Here we study the membrane-induced conformational change of Apo H by CD spectroscopy with two different model systems: anionic-phospholipid-containing liposomes [such as 1, 2-dimyristoyl-sn-glycero-3-phosphoglycerol (DMPG) and cardiolipin], and the water/methanol mixtures at moderately low pH, which mimic the micro-physicochemical environment near the membrane surface. It is found that Apo H undergoes a remarkable conformational change on interaction with liposomes containing anionic phospholipid. To interact with liposomes containing DMPG, there is a 6.8% increase in alpha-helix in the secondary structures; in liposomes containing cardiolipin, however, there is a 12.6% increase in alpha-helix and a 9% decrease in beta-sheet. The similar conformation change in Apo H can be induced by treatment with an appropriate mixture of water/methanol. The results indicate that the association of Apo H with membrane is correlated with a certain conformational change in the secondary structure of the protein. (+info)
Interaction between the lipoamide-containing H-protein and the lipoamide dehydrogenase (L-protein) of the glycine decarboxylase multienzyme system. 1. Biochemical studies.
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Lipoamide dehydrogenase or dihydrolipoamide dehydrogenase (EC 1.8.1. 4) is the E3-protein component of the mitochondrial 2-oxoacid dehydrogenase multienzyme complexes. It is also the L-protein component of the glycine decarboxylase system. Although the enzymology of this enzyme has been studied exhaustively using free lipoamide as substrate, no data are available concerning the kinetic parameters of this enzyme with its physiological substrates, the dihydrolipoyl domain of the E2 component (dihydrolipoyl acyltransferase) of the 2-oxoacid dehydrogenase multienzyme complexes or the dihydrolipoyl H-protein of the mitochondrial glycine decarboxylase. In this paper, we demonstrate that Tris(2-carboxyethyl)phosphine, a specific disulfide reducing agent, allows a continuous reduction of the lipoyl group associated with the H-protein during the course of the reaction catalysed by the L-protein. This provided a valuable new tool with which to study the catalytic properties of the lipoamide dehydrogenase. The L-protein displayed a much higher affinity for the dihydrolipoyl H-protein than for free dihydrolipoamide. The oxidation of the dihydrolipoyl H-protein was not affected by the presence of structurally related analogues (apoH-protein or octanoylated H-protein). In marked contrast, these analogues strongly and competitively inhibited the decarboxylation of the glycine molecule catalysed by the P-protein component of the glycine decarboxylase system. Small unfolded proteolytic fragments of the H-protein, containing the lipoamide moiety, displayed Km values for the L-protein close to that found for the H-protein. On the other hand, these fragments were not able to promote the decarboxylation of the glycine in the presence of the P-protein. New highly hydrophilic lipoate analogues were synthesized. All of them showed Km and kcat/Km values very close to that found for the H-protein. From our results we concluded that no structural interaction is required for the L-protein to catalyse the oxidation of the dihydrolipoyl H-protein. We discuss the possibility that one function of the H-protein is to maintain a high concentration of the hydrophobic lipoate molecules in a nonmicellar state which would be accessible to the catalytic site of the lipoamide dehydrogenase. (+info)
High affinity binding of beta 2-glycoprotein I to human endothelial cells is mediated by annexin II.
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Beta(2)-glycoprotein I (beta(2)GPI) is an abundant plasma phospholipid-binding protein and an autoantigen in the antiphospholipid antibody syndrome. Binding of beta(2)GPI to endothelial cells targets them for activation by anti-beta(2)GPI antibodies, which circulate and are associated with thrombosis in patients with the antiphospholipid antibody syndrome. However, the binding of beta(2)GPI to endothelial cells has not been characterized and is assumed to result from association of beta(2)GPI with membrane phospholipid. Here, we characterize the binding of beta(2)GPI to endothelial cells and identify the beta(2)GPI binding site. (125)I-beta(2)GPI bound with high affinity (K(d) approximately 18 nm) to human umbilical vein endothelial cells (HUVECs). Using affinity purification, we isolated beta(2)GPI-binding proteins of approximately 78 and approximately 36 kDa from HUVECs and EAHY.926 cells. Amino acid sequences of tryptic peptides from each of these were identical to sequences within annexin II. A role for annexin II in binding of beta(2)GPI to cells was confirmed by the observations that annexin II-transfected HEK 293 cells bound approximately 10-fold more (125)I-beta(2)GPI than control cells and that anti-annexin II antibodies inhibited the binding of (125)I-beta(2)GPI to HUVECs by approximately 90%. Finally, surface plasmon resonance studies revealed high affinity binding between annexin II and beta(2)GPI. These results demonstrate that annexin II mediates the binding of beta(2)GPI to endothelial cells. (+info)
Anti-beta2-glycoprotein I (GPI) autoantibodies, annexin V binding and the anti-phospholipid syndrome.
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We examined the role of autoantibodies to beta2-GPI and prothrombin (PT) in the inhibition of annexin V binding to cardiolipin (CL) and the association with clinical manifestations of the anti-phospholipid syndrome (APS). Plasma samples from 59 patients with anti-phospholipid (aPL) antibodies were studied. Affinity purification of total IgG and IgG anti-ss2-GPI antibodies was performed using staphylococcal protein A and phospholipid liposomes. Annexin V binding to CL was significantly inhibited by 31/59 (53%) aPL+ plasma samples. There was a significant association between annexin V inhibition and elevated levels of IgG anti-cardiolipin (aCL) (r = -0.62; P < 0.001), IgG anti-ss2-GPI (r = -0.67; P < 0. 001) and a weaker association with lupus anti-coagulant (r = -0.27; P = 0.05). There was no association with other isotypes of aCL and anti-ss2-GPI or with anti-PT of any isotype. In patients with clinical manifestations of the APS there were higher levels of IgG aCL (median (range) Z score): 10.0 (0-17.6) versus 5.0 (0-16.1); P = 0.03), IgG anti-ss2-GPI (4.5 (0-11.3) versus 0.9 (0-9.7); P = 0.02) and greater inhibition of annexin V binding to CL (-3.4 (-11.4-0.6) versus -1.1 (-10.8-1.2); P = 0.22). Odds ratios for the laboratory assays and the presence of clinical manifestations of the APS varied between 0.38 and 4.16, with the highest values for IgG aCL (4.16), IgG anti-ss2-GPI (3.28) and annexin V inhibition (2.85). Additional experiments with affinity-purified IgG antibodies indicated that inhibition of annexin V binding was dependent upon the concentration of ss2-GPI and anti-ss2-GPI antibodies. These results indicate that inhibition of annexin V binding to procoagulant phospholipid surfaces is dependent upon anti-ss2-GPI antibodies and suggest a role for annexin V in the pathogenesis of the APS. (+info)
Prospective evaluation of the frequency and clinical significance of antineutrophil cytoplasmic and anticardiolipin antibodies in community cases of patients with rheumatoid arthritis.
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OBJECTIVES: To evaluate the frequencies of antineutrophil cytoplasmic (ANCA), anticardiolipin (aCLA) and anti-beta(2)-glycoprotein 1 antibodies (abeta(2)-GP1A) in rheumatoid arthritis (RA) of limited duration in patients recruited primarily from private practitioners (80%), and to attempt to correlate the presence of these antibodies with certain clinical and/or biological criteria. Patients and methods. Patients (n = 102) with RA evolving for <5 yr (mean 2.2 yr) were recruited. A home evaluation collected clinical data [Ritchie articular index, Health Assessment Questionnaire (HAQ) index, extra-articular manifestations] and blood for biological analyses [C-reactive protein (CRP), rheumatoid factor, ANCA, aCLA, abeta(2)-GP1A]. ANCA were detected by indirect immunofluorescence on neutrophils and their specificity was determined by enzyme-linked immunosorbent assay (ELISA) and confirmed by immunoblotting; aCLA and abeta(2)-GP1A were detected by ELISA. RESULTS: Patients had mild RA (Ritchie = 11/78 +/- 9.6; HAQ = 0.79/3 +/- 0.7), probably due to the recruitment procedure. ANCA, aCLA and abeta(2)-GP1A frequencies were 18.5, 7 and 0%, respectively. Titres of ANCA and aCLA were low. A perinuclear ANCA staining pattern was exclusively observed and lactoferrin was shown to be the major antigen recognized. No relationship was found between ANCA and aCLA and/or rheumatoid factor, or any clinical manifestations. ANCA were more common in RA of longer duration (cut-off: 4 yr; P = 0.05) and aCLA were correlated with the CRP level (P = 0.05). CONCLUSIONS: In RA of recent onset, ANCA and aCLA were detected at low titres and frequencies, and were not associated with any clinical manifestations. A longitudinal study is needed to determine whether their early appearance is predictive of subsequent disease severity. (+info)
Anti-beta 2-glycoprotein I antibodies and anti-endothelial cell antibodies induce tissue factor in endothelial cells.
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Anti-beta 2-glycoprotein I antibodies bind to endothelial cells through beta 2-GPI. The antibodies are present in patients with systemic lupus erythematosus and antiphospholipid syndrome and are associated with the pathogenesis of the disease. Anti-endothelial cell antibodies that react with constitutive antigens on ECs are present in patients with vasculiditis and other diseases. Both types of antibodies can activate ECs. Frequent findings in APLS and vasculitis are fibrin deposits and thromboembolic phenomena. These indicate that the coagulation system is activated. However, the mechanism of activation is not clear. ECs generate tissue factor upon stimulation with various substances. In the present study we report that monoclonal anti-beta 2-GPI antibodies and AECAs, derived from a patient with primary APLS and a patient with Takayasu's arteritis, respectively, induce a potent tissue factor in ECs. The production of TF activity, TF antigen and TF mRNA is dose and time dependent. The TF activity was induced also by F(ab)2 but not by Fc fragments and was abolished completely by pre-incubation with ant-TF antibodies. The TF that is induced in ECs by AECAs with and without beta 2-GPI specificity may activate the coagulation and thereby play a major role in the pathogenesis of fibrin deposition and thrombus formation in diseases that are associated with the presence of these antibodies. (+info)