Microtitre plate and assay buffer alter detection of antiphosphatidylethanolamine antibodies in lupus anticoagulant positive plasma

Variability in Anticardiolipin Antibody Detection: Role of Nonspecific IgG Binding and Different Microtiter Plates

There are many studies that are available on the Internet that attempt to standardize the assay for anticardiolipin antibody evaluation because of the variability of results. The aim of this study was to evaluate simultaneously the role of different microplates and the importance of sample nonspecific binding in determining different results in anticardiolipin antibody detection. Sera from 8 patients with raised levels of IgG anticardiolipin antibodies and 10 control sera were assayed by enzyme-linked immunosorbent assay in the presence (specific binding) or in the absence of cardiolipin (sample blank) with four different microplates, that is, NUNC PolySorp, FALCON ProBIND, Greiner 655061 (high binding), and Greiner 655001 (medium binding). Results were expressed as optical densities or net-optical densities (following sample blank subtraction) as well as international IgG anticardiolipin units (GPL) or net-GPL. A wide interplate variability of optical densities was found. When results were expressed as GPL, significant differences were only found between Greiner 655061, FALCON ProBIND, and NUNC PolySorp ( P < .05 and P < .001, respectively) whereas differences were not statistically significant if interplate variability was analyzed as net-GPL. Results expressed as categorical variables (ie, positive/negative, according to a GPL cut-off and net-GPL cut-off, obtained with sera from 100 apparently healthy blood donors) showed a good or excellent Cohen's κ coefficient of concordance among plates when positivity was evaluated on net-GPL. Our data strongly suggest that quantification and subtraction of sample blank may improve both interlaboratory agreement and reliability of anticardiolipin assay and minimize false-positive results.

Influence of Phosphatidylethanolamine Concentration and Composition on the Detection of Antiphosphatidylethanolamine Antibodies by ELISA

BACKGROUND

Accumulating evidence supports a positive correlation between the presence of antiphosphatidylethanolamine (aPE) autoantibodies and clinical symptoms of antiphospholipid syndrome (APS). However, there is a lack of standardized ELISA-based method for detecting aPE. The current study was conducted to investigate the dependence of aPE ELISA on lipid concentration and composition of PE antigens.

METHODS

A range of ELISA conditions were examined by varying the concentrations of egg PE and by substituting egg PE with combinations of synthetic DOPE and DSPE. The physical properties of the synthetic PE species were also characterized.

RESULTS

Our data indicated that there are different optimal PE concentrations for conducting ELISA assays for cofactor-dependent and cofactor-independent aPEs. In addition, using a two-component synthetic lipid system, we demonstrated aPE ELISA readouts can be modulated to approach the performance level of egg PE, which is currently the most commonly used PE antigen.

CONCLUSION

These data raised the possibility of ultimately replacing natural PE antigens with a blend of defined synthetic lipid species, thus overcoming a known variable factor in aPE detection. The outcome of this study will help pave the way to developing a standardized aPE test.

Antiphosphatidylethanolamine antibodies and the antiphospholipid syndrome

The antiphospholipid antibodies included as laboratory criteria of the antiphospholipid syndrome (APS) are antibodies reacting with anionic phospholipids – anticardiolipin antibodies and lupus anticoagulant – and with β2-glycoprotein I. However, antibodies reacting with phosphatidylethanolamine (aPE), a zwitterionic phospholipid, have also been described to be associated with the main features of APS. The objectives of this review are to describe the characteristics of aPE and to bring attention to recent evidence that aPE are correlated with the main clinical features of APS, notably, in the absence of the laboratory criteria of this syndrome.

Antiphospholipid antibodies: laboratory and pathogenetic aspects

Antiphospholipid antibodies (aPL) constitute a heterogeneous group of autoantibodies that share the ability to bind phospholipids (PL) alone, protein-PL complexes, or PL-binding proteins. They have been detected in isolation, in association with autoimmune diseases such as systemic lupus erythematosus (SLE), and during the course of different infections. aPL have been associated with an array of clinical manifestations in virtually every organ, although deep vein and arterial thrombosis as well as pregnancy morbidity are predominant. The co-occurrence of these clinical findings with aPL constitutes the so-called antiphospholipid syndrome (APS). aPL can be detected by immunological methods [e.g., anticardiolipin antibodies (aCL)] or by functional methods that exploit the effect of aPL on blood coagulation [lupus anticoagulant (LA)]. Since aPL are heterogeneous, numerous immunological and coagulation assays have been developed. These assays have not been fully standardized, and, therefore, problems such as high interlaboratory variation are relatively frequent. Recently, recommendations have been published regarding LA and aCL testing. Not all aPL are pathogenic. However, when they are not associated with infections, they have a role in the pathogenesis of APS. Clinical and experimental data have shown that aPL exert their pathogenic activity by interfering with the function of coagulation factors, such as thrombin and factors X, XI and XII, and with the function of anticoagulant proteins of the protein C system. In addition, aPL interaction with platelets and endothelial cells induces a pro-adhesive activated phenotype.

Human autoantibodies to diacyl-phosphatidylethanolamine recognize a specific set of discrete cytoplasmic domains

The aim of this study was to characterize a novel human autoantibody-autoantigen system represented as cytoplasmic discrete speckles (CDS) in indirect immunofluorescence (IIF). A distinct CDS IIF pattern represented by 3-20 discrete speckles dispersed throughout the cytoplasm was identified among other cytoplasmic speckled IIF patterns. The cytoplasmic domains labelled by human anti-CDS-1 antibodies did not co-localize with endosome/lysosome markers EEA1 and LAMP-2, but showed partial co-localization with glycine-tryptophan bodies (GWB). CDS-1 sera did not react with several cellular extracts in immunoblotting and did not immunoprecipitate recombinant GW182 or EEA1 proteins. The typical CDS-1 IIF labelling pattern was abolished after delipidation of HEp-2 cells. Moreover, CDS-1 sera reacted strongly with a lipid component co-migrating with phosphatidylethanolamine (PE) in high performance thin-layer chromatography (HPTLC)-immunostaining of HEp-2 cell total lipid extracts. The CDS-1 major molecular targets were established by electrospray ionization-mass spectrometry (ESI-MS), HPTLC-immunostaining and chemiluminescent enzyme-linked immunosorbent assay as diacyl-PE species, containing preferentially a cis-C18 : 1 fatty acid chain at C-2 of the glycerol moiety, namely 1,2-cis-C18 : 1-PE and 1-C16 : 0-2-cis-C18 : 1-PE. The clinical association of CDS-1 sera included a variety of systemic and organ-specific autoimmune diseases but they were also observed in patients with no evidence of autoimmune disease.

Antiphospholipid antibodies: discovery, definitions, detection and disease

Antiphospholipid antibodies (aPL) are immunoglobulins of IgG, IgM and IgA isotypes that target phospholipid (PL) and/or PL-binding plasma proteins. Detection of aPL in the laboratory is done currently by both immunoassays and functional coagulation tests. Convention defines aPL specificity in immunoassays according to the particular PL substrate present, for example aPS represents antiphosphatidylserine antibodies. This may be technically incorrect inasmuch as a particular PL may be responsible for binding and highly concentrating a specific plasma protein, the latter then becomes the target for the aPL. The binding of beta(2)GP-I (apolipoprotein H) to the negatively charged PL, cardiolipin (CL) provides a good example of this circumstance. In contrast, aPL which specifically prolong coagulation times in in vitro are called lupus anticoagulants (LA). The precise PL target(s) of the aPL responsible for LA activities are unknown and often debated. The persistent finding of aPL in patients in association with abnormal blood clotting and a myriad of neurological, obstetrical and rheumatic disorders often compounded by autoimmune diseases has led to an established clinical diagnosis termed antiphospholipid syndrome (APS). The common denominator for these APS patients is the presence of circulating aPL on two or more occasions and the observation of events attributable to abnormal or accelerated blood clotting somewhere in vivo. The purpose of this review is to collect, collate, and consolidate information concerning aPL.

Antiphosphatidylethanolamine antibodies contribute to the diagnosis of antiphospholipid syndrome in patients with systemic lupus erythematosus

OBJECTIVE

To evaluate the correlation between antiphosphatidylethanolamine antibodies (aPE) and some antiphospholipid antibodies (aPL)-related clinical manifestations in patients with systemic lupus erythematosus (SLE).

METHODS

Patients with SLE (n=217) were tested for the presence of aPE, anticardiolipin antibodies (aCL), and lupus anticoagulant (LA). The prospective aPL-related clinical manifestations studied were: thrombosis, thrombocytopenia, recurrent fetal losses, heart valvulopathies, hemolytic anemia, livedo reticularis, and pulmonary hypertension.

RESULTS

A total of 109 SLE patients (50.23%) were IgG aPE-positive; 17.51% presented aPE as the sole autoantibody and had some clinical features of aPL-related clinical manifestations. IgG aPE were associated to the presence of heart valvulopathies (p=0.002). A statistical difference was also found when considering high levels of IgG aPE (O.D.>0.600) in patients with livedo reticularis (p=0.008).

CONCLUSION

The evaluation of IgG aPE may allow us to detect some more patients with aPL-related clinical manifestations in the SLE population, aPE correlated particularly with valvulopathies and livedo reticularis.

Anti-phosphatidylethanolamine (aPE) antibodies: a survey

Reports of anti-phosphatidylethanolamine antibodies (aPE) with similar or identical pathogenic associations as those described for anticardiolipin (aCL) and anti-phosphatidylserine (aPS) are found in the literature. In some instances, aPE is the sole antiphospholipid antibody (aPL) observed. Lupus anticoagulant antibodies (LA) appear to represent a subset of aPE as hexagonal phase PE can specifically inhibit the LA ability to prolong clotting times. As documented for aPL to the negatively charged phospholipids (PL), plasma proteins have been implicated for a positive aPE signal in the ELISA. Other aPE appear independent of known PE-binding plasma proteins. Among the described PE-binding proteins are high and low molecular weight kininogens (HMWK and LMWK) and the HMWK-binding proteins, factor XI and prekallikrein. Recently prothrombin has been added to this list. The reports of aPE published since 1986 are reviewed and discussed in this presentation.