Detection of antiphospholipid antibodies by immunostaining on thin layer chromatography plates

Current Promising Biomarkers and Methods in the Diagnostics of Antiphospholipid Syndrome: A Review

Antiphospholipid syndrome (APS) is a hypercoagulation condition associated with the incidence of heterogenic antiphospholipid antibodies (aPLs), which non-specifically affect hemostasis processes. APS is clinically manifested by recurrent arterial and venous thromboses and reproduction losses. The aPL antibodies, which may induce clinical manifestations of APS, include criteria antibodies anti-cardiolipin, anti-β2-glycoprotein-I, and lupus anticoagulant, but also non-criteria antibodies, for example anti-β2-glycoprotein-I domain I, anti-phosphatidylserine/prothrombin, anti-annexin V, and many others. APS occurs mostly in patients of younger and middle age, most frequently in females. Laboratory diagnostics of APS are quite difficult, as they include a wide spectrum of examining methods, which are based on various principles of detection and are performed using various laboratory techniques. The objective of the review is to describe the current state of potentially examined biomarkers and methods in APS diagnostics. The aforementioned biomarkers are lupus anticoagulant, anti-β2-glycoprotein-I, anti-cardiolipin, anti-β2-glycoprotein-I domain I, anti-phosphatidylserine/prothrombin, anti-β2-glycoprotein-I IgA, anti-cardiolipin IgA, anti-annexin V and II, anti-prothrombin, anti-cardiolipin/vimentin, anti-protein S/protein C, and antibodies against phospholipid antigens for whose diagnostics we may use some of the methods established for a long time and some of the modern methods—the coagulation method for the determination of lupus anticoagulant (LA), enzyme-linked imunosorbent assay (ELISA), chemiluminescence analysis (CLIA), multiplex fluorescence flow immunoassay (MFFIA), fluorescence enzyme immunoassay (EliA), line immunoassay (LIA), multiline dot assay (MLDA), and thin-layer chromatography (TLC). Conclusion: Antibodies against phosphatidylethanolamine, phosphatidic acid, phosphatidylserine, phosphatidylinositol, cardiolipin/vimentin complex, and annexin V are currently the most studied new markers. However, these assays have not been standardized until now, both from the laboratory and clinical point of view. In this review we summarize the evidence of the most studied aPL markers and their potential clinical significance in seronegative APS (SN-APS).

[Seronegative antiphospholipid syndrome: Myth or reality?]

The antiphospholipid syndrome (APS) is a systemic autoimmune disease characterized by thrombosis and/or obstetrical manifestations and the persistent presence, at least 12 weeks apart, of antiphospholipid antibodies (aPL) such as lupus anticoagulant (LA) and/or anticardiolipin antibodies (ACL) and/or anti-β2 glycoprotein I antibodies (aβ2GPI). The finding of patients with clinical profile highly suggestive of APS but who are negative for conventional biological criteria has led to the concept of seronegative APS. In the last few years, new antigen targets and methodological approaches have been employed to more clearly identify this syndrome in patients with thrombosis or obstetrical complications without conventional aPL. Although seronegative APS is still controversial, there is increasing recognition of the existence of this subgroup. However, clinical relevance of non conventional aPL need to be confirmed by efforts toward standardizing new biological tools and longitudinal studies involving large cohort of patients.

Does seronegative obstetric APS exist? "pro" and "cons"

Antiphospholipid Syndrome (APS) is the commonest treatable cause of recurrent miscarriage and pharmacological treatment of pregnant patients with antiphospholipid antibodies (aPL) should aim at preventing obstetric complications and maternal thrombotic events. Conventional treatment for patients with an established diagnosis of obstetric APS (OAPS), generally resulting in over 70-80% successful pregnancies. Since seropositive (SP)-APS and seronegative (SN)-APS patients had shown similar clinical profiles, patients with SN- OAPS, as well as SP-OAPS, should receive combined treatment in order to improve the pregnancy prognosis; indeed, current standard of care increased good pregnancy outcome in SN-APS, with similar effect to confirmed APS. The above data suggest that there are patients with the clinical manifestations of OAPS but persistently negative to conventional aPL that need to be identified to ensure adequate therapy and therefore a better prognosis. The clinical utility of non-criteria aPL in the diagnosis of SN-APS is still a matter of debate. In the last decade more and more studies have reported the presence of patients suffering from SN-APS in which non-conventional ("non-criteria") aPL might be present or antibodies may be detected using methodological approaches different from the traditional assays. To improve test standardization large prospective, multicenter, and multinational studies are needed. Therefore, when assessing a patient with clinical manifestations consistent with OAPS but aPL negative using the conventional available assays, the clinician should consider the possibility that the patient is affected with SN-APS.

Coupling of In Vitro Bioassays with Planar Chromatography in Effect-Directed Analysis

Modern analytical test methods increasingly detect anthropogenic organic substances and their transformation products in water samples and in the environment. The presence of these compounds might pose a risk to the aquatic environment. To determine a possible (eco)toxicological risk, aquatic samples are tested using various bioassays, including sub-organismic assays such as the luminescent bacteria inhibition test, the acetylcholinesterase inhibition test, and the umu-test. The effect-directed analysis (EDA) combines physicochemical separation methods with biological (in vitro) tests. High-performance thin-layer chromatography (HPTLC) has proved to be particularly well suited for the separation of organic compounds and the subsequent analysis of effects by the application of the biotests directly on the surface of the HPTLC plate. The advantage of using HPTLC in comparison to high-performance liquid chromatography (HPLC) for EDA is that the solvent which is used as a mobile phase during chromatography is completely evaporated after the separation and therefore can no longer influence the applied bioassays.A prioritization during the complex identification process can be achieved when observed effects are associated with the separated zones in HPTLC. This increases the probability of identifying the substance responsible for an adverse effect from the multitude of organic trace substances in environmental samples. Furthermore, by comparing the pattern of biological effects of a separated sample, it is possible to track and assess changes in biological activity over time, over space, or in the course of a process, even without identifying the substance. HPTLC has already been coupled with various bioassays.Because HPTLC is a very flexible system, various detection techniques can be used and combined. In addition to the UV/Vis absorption and fluorescence measurements, TLC can also be coupled with a mass spectrometer (MS) for compound identification. In addition, detection of functional groups by means of derivatization reagents can support this identification. It is also possible to combine derivatization and HPLC-MS.Two case studies are used to illustrate the significance of HPTLC-EDA in investigating water quality: Study on a wastewater treatment plant Possible influence of an artificial turf surface on ground water.

Altered Traffic of Cardiolipin during Apoptosis: Exposure on the Cell Surface as a Trigger for "Antiphospholipid Antibodies"

Apoptosis has been reported to induce changes in the remodelling of membrane lipids; after death receptor engagement, specific changes of lipid composition occur not only at the plasma membrane, but also in intracellular membranes. This paper focuses on one important aspect of apoptotic changes in cellular lipids, namely, the redistribution of the mitochondria-specific phospholipid, cardiolipin (CL). CL predominantly resides in the inner mitochondrial membrane, even if the rapid remodelling of its acyl chains and the subsequent degradation occur in other membrane organelles. After death receptor stimulation, CL appears to concentrate into mitochondrial “raft-like” microdomains at contact sites between inner and outer mitochondrial membranes, leading to local oligomerization of proapoptotic proteins, including Bid. Clustering of Bid in CL-enriched contacts sites is interconnected with pathways of CL remodelling that intersect membrane traffic routes dependent upon actin. In addition, CL association with cytoskeleton protein vimentin was observed. Such novel association also indicated that CL molecules may be expressed at the cell surface following apoptotic stimuli. This observation adds a novel implication of biomedical relevance. The association of CL with vimentin at the cell surface may represent a “new” target antigen in the context of the apoptotic origin of anti-vimentin/CL autoantibodies in Antiphospholipid Syndrome.

"New" antigenic targets and methodological approaches for refining laboratory diagnosis of antiphospholipid syndrome

Antiphospholipid antibodies (aPLs) are a heterogeneous group of antibodies directed against phospholipids or protein/phospholipid complexes. Currently, aPLs are assessed using either "solid-phase" assays that identify anticardiolipin antibodies and anti-β2-glycoprotein I antibodies or "liquid-phase" assay that identifies lupus anticoagulant. However, in the last few years, "new" antigenic targets and methodological approaches have been employed for refining laboratory diagnosis of antiphospholipid syndrome (APS). In this review the potential diagnostic value of antibodies to domains of β2-GPI, prothrombin/phosphatidylserine, vimentin/cardiolipin, protein S, protein C, annexin A2, annexin A5, and phospholipid antigens is discussed. Moreover, new technical approaches, including chemiluminescence, multiline dot assay, and thin layer chromatography (TLC) immunostaining, which utilize different supports for detection of aPL, have been developed. A special focus has been dedicated on "seronegative" APS, that is, those patients with a clinical profile suggestive of APS (thromboses, recurrent miscarriages, or foetal loss), who are persistently negative for the routinely used aPL. Recent findings suggest that, in sera from patients with SN-APS, antibodies may be detected using "new" antigenic targets (mainly vimentin/cardiolipin) or methodological approaches different from traditional techniques (TLC immunostaining). Thus, APS represents a mosaic, in which antibodies against different antigenic targets may be detected thanks to the continuously evolving new technologies.

The mosaic of "seronegative" antiphospholipid syndrome

In the clinical practice it is possible to find patients with clinical signs suggestive of antiphospholipid syndrome (APS), who are persistently negative for the laboratory criteria of APS, that is, anti-cardiolipin antibodies (aCL), anti-β2-GPI antibodies and lupus anticoagulant. Therefore, it was proposed for these cases the term of seronegative APS (SN-APS). In order to detect autoantibodies with different methodological approaches, sera from 24 patients with SN-APS were analysed for anti-phospholipid antibodies using TLC immunostaining, for anti-vimentin/cardiolipin antibodies by enzyme-linked immunosorbent assay (ELISA), and for anti-annexin V and anti-prothrombin antibodies by ELISA and dot blot. Control groups of our study were 25 patients with APS, 18 with systemic lupus erythematosus (SLE), and 32 healthy controls. Results revealed that 13/24 (54.2%) SN-APS sera were positive for aCL (9 of whom were also positive for lysobisphosphatidic acid) by TLC immunostaining, 11/24 (45.8%) for anti-vimentin/cardiolipin antibodies, 3/24 (12.5%) for anti-prothrombin antibodies, and 1/24 (4.2%) for anti-annexin V antibodies. These findings suggest that in sera from patients with SN-APS, antibodies may be detected using "new" antigenic targets (mainly vimentin/cardiolipin) or methodological approaches different from traditional techniques (mainly TLC immunostaining). Thus, SN-APS represents a mosaic, in which antibodies against different antigenic targets may be detected.

TLC immunostaining for detection of "antiphospholipid" antibodies

Thin-layer chromatography (TLC) is a nonquantitative technique, which has been employed in the detection of antiphospholipid (aPL) antibodies. Antiphospholipid syndrome (APS) is the most frequently acquired thrombophilia, characterized by thrombosis and obstetric manifestations associated to an autoimmune trait, represented by the positivity of antiphospholipid (aPL) antibodies. Immunoassays for anticardiolipin (aCL) and anti-β2 glycoprotein I (aβ2GPI) antibodies and clotting tests for lupus anticoagulant (LA) represent the standard tests for the routine detection of aPL. The term "seronegative APS" has been used to describe patients with clinical manifestation of APS and persistently negative aPL assessed with routine assays. TLC immunostaining is a useful method for the detection of different antigenic targets of "antiphospholipid" antibodies; it is able to identify the reactivity of serum aPL experimented with purified phospholipid molecules with a different exposure compared to ELISA methods. This method seems to be applicable in patients who repeatedly tested negative for the standard aPL, i.e., aCL, aβ2GPI, and LA. Therefore, this technique may be proposed as a second step test for the diagnosis of APS.

Thin-layer chromatography immunostaining in detecting anti-phospholipid antibodies in seronegative anti-phospholipid syndrome

In clinical practice it is possible to find patients with clinical signs suggestive of anti-phospholipid syndrome (APS) who are persistently negative for the routinely used anti-phospholipid antibodies (aPL). Therefore, the term proposed for these cases was seronegative APS (SN-APS). We investigated the clinical usefulness of thin-layer chromatography (TLC) immunostaining in detecting serum aPL in patients presenting clinical features of SN-APS. Sera from 36 patients with SN-APS, 19 patients with APS, 18 patients with systemic lupus erythematosus (SLE), 20 anti-hepatitis C virus (HCV)-positive subjects and 32 healthy controls were examined for aPL using TLC immunostaining. Anti-β(2) -glycoprotein-I, anti-annexin II, anti-annexin V and anti-prothrombin antibodies were tested by enzyme-linked immunosorbent assays (ELISA). Eahy926, a human-derived endothelial cell line, was incubated with immunoglobulin (Ig)G fraction from SN-APS patients and analysis of phospho-interleukin (IL)-1 receptor-associated kinase (IRAK) and phospho-nuclear factor (NF)-κB was performed by Western blot, vascular cell adhesion molecule 1 (VCAM-1) expression by cytofluorimetric analysis and supernatants tissue factor (TF) levels by ELISA. TLC immunostaining showed aPL in 58·3% of SN-APS patients: anti-cardiolipin in 47·2%, anti-lyso(bis)phosphatidic acid in 41·7% and anti-phosphatidylethanolamine in 30·5%. Six of 36 patients showed anti-annexin II. Incubation of Eahy926 cells with IgG from SN-APS induced IRAK phosphorylation, NF-κB activation, VCAM-1 surface expression and TF cell release. TLC immunostaining could identify the presence of aPL in patients with SN-APS. Moreover, the results suggest the proinflammatory and procoagulant effects in vitro of these antibodies.

Detection of antiphospholipid antibodies by automated chemiluminescence assay

The laboratory diagnosis of antiphospholipid antibody syndrome (APS) requires the demonstration of antiphospholipid antibodies (aPL) by lupus anticoagulant (LAC) measured through coagulation assays, anticardiolipin IgG or IgM antibodies (aCL) and/or anti-β2-glycoprotein I IgG or IgM antibodies (anti-β2-GPI), usually detected by ELISA. In this study we tested aCL by a new automated system using the chemiluminescence principle. Our results showed that, while almost all the sera from APS patients, positive for IgG aCL and anti-β2-GPI by ELISA, were also positive for IgG aCl by chemiluminescence, only 30.13% of patients without clinical manifestations of APS, but positive for aCL and persistently negative for anti-β2-GPI (by ELISA) and LA, confirmed the positive test by chemiluminescence. This difference was highly significant (p<0.0001). Interestingly, this test also prompted to identify 20% of patients positive for LA, but persistently negative for both aCL and anti-β2-GPI IgG (ELISA). Thus, the new technology of automated chemiluminescence assay for measuring aPL may represent an useful tool to identify "true" APS patients.

Does seronegative antiphospholipid syndrome really exist?

The diagnosis of seronegative (SN-) antiphospholipid syndrome (APS) has been suggested for patients with clinical manifestations indicative of APS but with persistently negative results in the commonly used assays to detect anti-cardiolipin (aCL) antibodies, anti-β2 Glycoprotein I antibodies (aβ2GPI), and lupus anticoagulant (LA). To date the best management of these patients is still unclear. New emerging anti-phospholipid (aPL) assays could improve our ability in diagnosing APS. However, the availability of aPL assays in routine laboratory practice is limited. In fact, even aβ2GPI is routinely tested in only a small number of laboratories, and other aPL, such as anti-prothrombin or anti-annexin antibodies, in only a few research laboratories. On the other hand transient or false negative aPL assay and other genetic or acquired pro-thrombotic conditions can further complicate this issue. This paper is focused on the arguments for and against the diagnosis of SN-APS and is aimed to help the clinician when approaching a patient with clinical manifestations consistent with APS diagnosis but with negative aPL using the commonly available tests.

Vimentin/cardiolipin complex as a new antigenic target of the antiphospholipid syndrome

Antiphospholipid syndrome (APS) is an autoimmune disease characterized by arterial and venous thrombosis, recurrent abortions, and antiphospholipid antibodies (aPL). However, it is possible to find patients with clinical signs of APS who persistently test negative for aPL (seronegative APS, or SN-APS). The aim of this study was to identify new antigenic target(s) of autoantibodies in APS patients, which may also be recognized in SN-APS. We tested sera from patients with SN-APS with a proteomic approach by analyzing endothelial cell-surface membrane proteins. Sera from SN-APS patients revealed 2 reactive spots corresponding to vimentin, a protein that is shown to bind cardiolipin in vitro. Antivimentin/cardiolipin antibodies were tested in 29 SN-APS patients, 40 APS patients, 30 patients with systemic lupus erythematosus, 30 with rheumatoid arthritis, 30 with venous or arterial thrombosis, and 32 healthy control patients. We observed that not only a large proportion of SN-APS patients but also almost all the APS patients displayed the presence of antivimentin/cardiolipin antibodies. To verify the possible pathogenic role of these autoantibodies, we demonstrated that affinity-purified antivimentin/cardiolipin antibodies induced interleukin receptor-associated kinase phosphorylation and nuclear factor-κB activation in endothelial cells. Our results prompt to identify vimentin as a "new" cofactor for aPL, which may represent a useful tool mainly in SN-APS patients.

Management of the antiphospholipid syndrome

Antiphospholipid syndrome (APS) is characterized by recurrent venous or arterial thromboses, fetal losses and thrombocytopenia in the presence of antiphospholipid antibodies, namely lupus anticoagulant, anticardiolipin antibodies or antibodies directed to various proteins, mainly β2 glycoprotein I, or all three. There is consensus in treating patients with APS and first venous thrombosis with oral anticoagulation to a target international normalized ratio (INR) of 2.0-3.0. A recent systematic review recommended a target INR of >3.0 in those patients with APS and arterial thrombosis. The approach in women with obstetric manifestations of APS is based on the use of aspirin plus heparin. The best treatment for patients with the catastrophic variant of the APS is a combination of anticoagulation, corticosteroids, and plasma exchange or intravenous immunoglobulins.

Sixth meeting of the European Forum on antiphospholipid antibodies. How to improve the understanding of the antiphospholipid syndrome?

The main objective of these meetings is to promote international collaboration in various clinical and research projects. This paper is the summary of the 2007 Ljubljana meeting, and offers an overview of the proposed projects. The technical and methodological details of the projects will be published on the forum’s web site (http://www.med.ub.es/MIMMUN/FORUM/STUDIES.HTM).

Antiphospholipid reactivity against cardiolipin metabolites occurring during endothelial cell apoptosis

We have recently shown that cardiolipin (CL) and its metabolites move from mitochondria to other cellular membranes during death receptor-mediated apoptosis. In this study, we investigate the immunoreactivity to CL derivatives occurring during endothelial apoptosis in patients with antiphospholipid syndrome (APS) and systemic lupus erythematosus (SLE). We compared the serum immunoreactivity to CL with that of its derivatives monolysocardiolipin (MCL), dilysocardiolipin (DCL), and hydrocardiolipin (HCL) by means of both enzyme-linked immunosorbent assay and thin-layer chromatography (TLC) immunostaining. In addition, we investigated the composition of phospholipid extracts from the plasma membrane of apoptotic endothelial cells and the binding of patients' sera to the surface of the same cells by using high-performance TLC and immunofluorescence analysis. The average reactivity to MCL was comparable with that of CL and significantly higher than that for DCL and HCL in patients studied, both in the presence or in the absence of beta₂-glycoprotein I. Of relevance for the pathogenic role of these autoantibodies, immunoglobulin G from patients' sera showed an increased focal reactivity with the plasma membrane of endothelial cells undergoing apoptosis. Interestingly, the phospholipid analysis of these light membrane fractions showed an accumulation of both CL and MCL. Our results demonstrated that a critical number of acyl chains in CL derivatives is important for the binding of antiphospholipid antibodies and that MCL is an antigenic target with immunoreactivity comparable with CL in APS and SLE. Our finding also suggests a link between apoptotic perturbation of CL metabolism and the production of these antibodies.

Cardiolipin and its metabolites move from mitochondria to other cellular membranes during death receptor-mediated apoptosis

We previously reported that during death receptor-mediated apoptosis, cardiolipin (CL) relocates to the cell surface, where it reacts with autoantibodies from antiphospholipid syndrome sera. Here, we analysed the intracellular distribution of CL and its metabolites during the early phase of cell death signalling triggered by Fas stimulation in U937 cells and mouse liver. We found a redistribution of mitochondrial CL to the cell surface by using confocal microscopy and flow cytometry. Mass spectrometry revealed that CL and its metabolites relocated from mitochondria to other intracellular organelles during apoptosis, with a conversion into non-mitochondrial lipids. Concomitantly, cytosolic Bid relocated to the light membranes comprised in fraction P100, including the plasma membrane and associated vesicular systems. A direct Bid-CL interaction was demonstrated by the observation that CL and monolysoCL coimmunoprecipitated with Bid especially after Fas stimulation, suggesting a dynamic interaction of the protein with CL and its metabolites.

Glycolipids of Mycobacterium tuberculosis strain H37Rv are potential serological markers for diagnosis of active tuberculosis

A simple and cost-effective diagnostic tool (TB Screen Test) for the screening of patients with pulmonary and extrapulmonary tuberculosis and for differentiation of those individuals from individuals without tuberculosis, other common infections, and healthy controls has been developed. The serological responses of purified mycobacterial glycolipid antigens were examined by a liposome agglutination assay. The assay was able to detect very low antiglycolipid antibody concentrations in the infected individuals. The sera from the tuberculosis patient group had significantly higher concentrations of antiglycolipid antibody than the sera from uninfected control subjects, with 94% sensitivity and 98.3% specificity. Glycolipids of Mycobacterium tuberculosis H37Rv antigens were isolated, purified, and characterized. After interchelation with liposome particles, these purified antigens specifically bound to the antiglycolipid antibodies present in the sera of patients with tuberculosis, resulting in the formation of a blue agglutination. This protocol clearly differentiates healthy controls and M. bovis BCG-vaccinated subjects from those with active tuberculosis. The resultant diagnostic tool, the TB Screen Test, is more economical and rapid (4 min) than other currently available products and can be used for the mass screening of a heavily afflicted population.

New Facet of Antiphospholipid Antibodies

Since the aCL test was first described, several reports have described the heterogeneity of aPL, which binds to different anionic phospholipids, proteins, or to a phospholipid-protein complex. It has been recently reported that antiphospholipids (aPLs) from the sera of patients with the antiphospholipid syndrome (APS) are able to bind some newly identified antigens, the lyso(bis)phosphatidic acid (LBPA), lipid restricted to the late endosomes, and the sulfatides, acidic glycosphingolipids involved in the hemostatic process. Of interest, aLBPAs are present in the sera of a large number of patients with APS showing similar sensitivity and specificity compared to anti-beta(2) glycoprotein I antibodies (abeta(2)-GPIs) and close association with lupus anticoagulant. Moreover, beta(2)-GPI binds to sulfatides and the majority of the aPL reacting with cardiolipin-beta(2)-GPI complex also react with the sulfatide-beta(2)-GPI complex. Different mechanisms involved in the production of autoantibodies in autoimmune diseases have been proposed and, among them, apoptosis or programmed cell death seems to play a leading role. The relocation of CL and its metabolites during apoptosis may represent an in vivo trigger for the generation of aCL, and the higher reactivity of sera from APS patients to monolysocardiolipin, the immediate degradation product of mitochondrial CL validates this hypothesis. Finally, increasing evidence suggests that oxidative stress could be a pathogenic link between aPL and thrombosis, and antioxidant treatment may have some efficacy in preventing the clinical manifestations of this syndrome.

Anti-lysobisphosphatidic acid antibodies in patients with antiphospholipid syndrome and systemic lupus erythematosus

Lyso(bis)phosphatidic acid (LBPA) is a novel antigenic target in anti-phospholipid syndrome (APS) and antibodies directed against LBPA (aLBPA) have been detected in sera from APS patients. In this study we first evaluated aLBPA in comparison with the most widely used methods (i.e. anticardiolipin [(aCL)-enzyme-linked immunosorbent assay (ELISA)] and antibeta-2-glycoprotein-I antibodies (abeta(2)-GPI-ELISA) utilized to detect antiphospholipid antibodies in patients with primary or secondary APS, systemic lupus erythematosus, chronic HCV infection and healthy subjects. We then assessed the relationship between aLBPA, lupus anticoagulant (LAC) and the main clinical manifestations of APS. Finally, we evaluated the presence of 'pure' (i.e. beta(2)-GPI-independent) aLBPA in patients with APS and controls. The results indicate that aLBPA as well as abeta(2)-GPI display higher specificity but lower sensitivity for APS compared to aCL. Moreover, serum aLBPA correlate closely with aCL and abeta(2)-GPI in APS patients and are strictly associated with LAC positivity. We demonstrate that beta(2)-GPI binds to LBPA with affinity similar to CL, and antibodies able to react with phosholipid-protein complex exist; however, 'pure' aLBPA can also be detected in sera of APS patients. Altogether these data confirm that LBPA may be an antigenic target in APS and that aLBPA are serological markers of APS with similar sensitivity and specificity compared to abeta(2)-GPI. However, the clinical utility of aLBPA detection alone or in combination with aCL and/or abeta(2)-GPI remains to be elucidated in larger and longitudinal studies.

Cardiolipin on the surface of apoptotic cells as a possible trigger for antiphospholipids antibodies

This study provides evidence that cardiolipin (CL) molecules are expressed on the surface of apoptotic cells and are recognized by antiphospholipid antibodies, purified from patients with the antiphospholipid antibody syndrome (APS). CL expression on cell surface was demonstrated by high performance thin layer chromatography analysis of phospholipids from plasma membrane purified fractions and by the positive staining with the CL-specific dye nonyl-acridine orange. This finding was complemented with the observation that aCL IgG purified from patients with APS bind to the surface of apoptotic cells. This staining shows a clustered distribution mostly localized on surface blebs. Interestingly, CL exposure on the cell surface preceded the DNA fragmentation, as shown by cytofluorimetric analysis. These findings demonstrate that exposure of CL molecules on the cell plasma membrane is an early event of the apoptotic cellular program that may represent an in vivo trigger for the generation of aCL.

Specificity of anti-phospholipid antibodies in infectious mononucleosis: a role for anti-cofactor protein antibodies

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.

Apoptosis and antiphospholipid antibodies

OBJECTIVE

To analyze the potential links between antiphospholipid antibodies (aPL) and apoptosis in the pathogenesis of the antiphospholipid antibody syndrome (APS).

METHODS

A review was undertaken of the most relevant scientific literature on apoptosis and autoimmune phenomena. Experimental and human pathology were reviewed to substantiate the hypothesis that apoptosis is involved in the generation of aPL.

RESULTS

Several considerations suggest that exposure of phospholipids (PL) during apoptosis may be a driving antigenic stimulus to the production of aPL. Furthermore, the molecular PL-protein complexes formed during apoptosis are targeted by "pathogenic" aPL. The binding and the clearance of apoptotic cells by these autoantibodies likely further enhances the aPL immune response. Experimental models and human pathology suggest that a restricted genetic background is key to the development of this immune response.

CONCLUSIONS

Abnormalities of apoptosis observed in the course of autoimmune conditions likely provide an antigenic stimulus to the production of aPL.

Anti-cardiolipin antibodies are associated with anti-endothelial cell antibodies but not with anti-beta 2 glycoprotein I antibodies in HIV infection

HIV infection is associated with polyclonal increase in serum immunoglobulins and with elevated titers of serum antibodies to a variety of self antigens, including anti-phospholipid antibodies. In the present study, we found a high prevalence of 46.8% of serum IgG anticardiolipin antibodies (ACA) in a group of 111 unselected HIV-seropositive individuals. The presence of ACA was correlated with that of IgG antibodies to endothelial cells (AECA) but not with that of anti-beta 2 glycoprotein I antibodies, that were only found in 7.4% of the patients. The presence of IgG ACA was not associated with detectable lupus anticoagulant activity, nor with a history of thrombosis. Serum titers of ACA were not correlated with absolute numbers of circulating CD4+ cells. We found no relationship between the presence and titers of ACA, hypergammaglobulinemia, and serum titers of natural IgG autoantibodies to a panel of self antigens. Our results suggest that increased titers of ACA in HIV infection result from a biased expansion of B cell clones producing natural autoantibodies.