Demonstration of high specificity antibodies against phosphatidylserine

The distribution and function of phosphatidylserine in cellular membranes

Phosphatidylserine (PS) is the most abundant negatively charged phospholipid in eukaryotic membranes. PS directs the binding of proteins that bear C2 or gamma-carboxyglutamic domains and contributes to the electrostatic association of polycationic ligands with cellular membranes. Rather than being evenly distributed, PS is found preferentially in the inner leaflet of the plasma membrane and in endocytic membranes. The loss of PS asymmetry is an early indicator of apoptosis and serves as a signal to initiate blood clotting. This review discusses the determinants and functional implications of the subcellular distribution and membrane topology of PS.

Antigenic Prenylated Peptide Conjugates and Polyclonal Antibodies To Detect Protein Prenylation

Posttranslational modification of proteins with farnesyl and geranylgeranyl groups is a required modification for signaling proteins that includes the small GTPases in the Ras, Rho, and Rab families, heterotrimeric G proteins, and nuclear lamin proteins. To develop antibodies capable of detecting and distinguishing prenylated proteins, we synthesized two antigens, succinylglycine-(geranylgeranyl)cysteine methyl ester (SuccG-(gg)CMe, 1) and succinylglycine-(farnesyl)cysteine methyl ester (SuccG-(f)CMe, 2). These prenylated peptides were covalently coupled to bovine serum albumin (BSA) and to keyhole limpet hemocyanin (KLH) to produce polyvalent, immunogenic bioconjugates. Immunization of rabbits with these immunogens generated polyclonal antisera that contained significant titers of anti-geranylgeranyl and anti-farnesyl antibodies. The selectivity of the polyclonal antisera was examined using ELISA and dot blotting methods. The anti-farnesyl and anti-geranylgeranyl antisera crossreacted with both antigens. Attempts to purify the polyclonal antisera by either positive or negative immunoaffinity selection protocols failed to produce selective anti-geranylgeranyl and anti-farnesyl antibodies. Moreover, both crude antisera and purified antibodies also crossreacted with myristoylated and palmitoylated BSA conjugates. Immunofluorescence staining of EYFP-CVLL or EYFP-CVIM transfected CHO-K1 cells with rabbit polyclonal antisera showed colocalized membrane fluorescence. Thus, an important caveat for the use of antibodies raised against aliphatic antigens is that extensive controls must be performed to determine selectivity.

Lipids are co-eluted with immunoglobulins G during purification by recombinant streptococcal protein G affinity chromatography

The efficiency of recombinant streptococcal protein G (rec-spG) affinity column chromatography in purifying immunoglobulins G (IgG) from lipids has been studied, with particular reference to IgG fractions from bronchoalveolar lavage (BAL) fluid and serum samples from different sources. It was found that the IgG fractions purified by rec-spG affinity column chromatography also contained cholesterol and phospholipids.

Immunocytochemistry of lipids: chemical fixatives have dramatic effects on the preservation of tissue lipids

We report here the effects of chemical fixatives on lipids studied under conditions simulating the immunogold labelling of phosphatidylserine. Using anti-phosphatidylserine antibodies, it is shown that the labelling intensity of a phosphatidylserine/phosphatidylcholine coating depends largely on the conditions of fixation. In fact, the usual aldehydic fixatives washed out most of the phostphatidylserine, thus preventing the binding of anti-phosphatidylserine antibodies. This was confirmed on biological samples such as rat liver and brain by measuring the loss of radiolabelled lipids during the fixation procedure. Furthermore, the complete procedure of tissue preparation for electron microscopical observation was investigated. The loss of (radiolabelled) lipids was studied in tissue samples during fixation and resin embedding. The results showed that the classical procedure (glutaraldehyde fixation followed by epoxy resin embedding) results in the loss of 73-91% of the tissue lipids whereas in unfixed, freeze-substituted samples, more than 76% of the tissue lipids are preserved.

Antibodies to long-chain acyl-CoAs. A new tool for lipid biochemistry

Antibodies directed against long chain acyl-CoAs (having 16 and 18 carbon atoms) have been prepared and are reported for the first time. A modified ELISA procedure adapted to these amphiphilic molecules has been developed: it is a rapid, simple and sensitive test permitting to detect as little as 3 pmol of acyl-CoA. These antibodies represent a new tool for studying long-chain acyl-CoAs. Their use in an immunochemical approach for the study of protein-acyl-CoA interactions is presented.

Monoclonal antibodies directed against the E2 protein (MIC2 gene product) induce exposure of phosphatidylserine at the thymocyte cell surface

Monoclonal antibodies (mAbs) directed against E2, a 32-kDa transmembrane protein encoded by the MIC2 gene located in the pseudoautosomal region, induce a transbilayer movement of phosphatidylserine and, to a lesser extent, phosphatidylethanolamine in human thymocytes and a Jurkat T lymphocytes. The translocation of phosphatidylserine has been evidenced by using either derivatization of anionic phospholipids with trinitrobenzenesulfonate (TNBS) or cytofluorimetry after labeling of cells with antiphosphatidylserine antibodies. The perturbation of membrane phospholipids induced by anti-E2 mAbs was further evidenced by labeling the cells with merocyanine 540. The specificity of anti-E2-induced perturbations of membrane asymmetry was tested by using a number of mAbs able to activate T cells, including CD3 and CD2. The results strongly suggest that anti-E2-induced changes in PtdSer are related to cell aggregation since the same mAbs specifically induce the aggregation of both thymocytes and Jurkat cells and since the E2 molecule has been previously implicated in the adhesive properties of human T cells with erythrocytes.

Silica-ELISA method improves detection and quantitation of minor glycolipid components in lipid mixtures and of other antigens

This paper describes a new type of ELISA plate in which the reaction wells have been coated with silica gel. ELISA using these prototype silica-ELISA plates is markedly more sensitive for glycolipid antigens in lipid mixtures than ELISA using polystyrene plates without silica. Silica-ELISA plates also improve the analysis of certain protein and carbohydrate antigens. This technology may be of considerable benefit in the analysis of minor lipids and other antigens from human brain, cerebrospinal fluid or blood.

Demonstration that anti-phospholipid auto-antibodies react with both anionic and zwitterionic phospholipids

The specificity of anti-phospholipid auto-antibodies present in the serum of systemic lupus erythematosus patients towards the phospholipids has been studied by two different methods. The antibodies have been characterized either after affinity purification or by inhibition experiments. Our results clearly demonstrate that anti-phospholipid auto-antibodies recognize all phospholipids, whatever their polar head.

Autoantibodies against all the phospholipids: a comparative systematic study with systemic lupus erythematosus and healthy sera

The sera of systemic lupus erythematosus patients were tested by ELISA for the presence of autoantibodies against all the phospholipids: cardiolipin, phosphatidic acid, phosphatidylcholine, phosphatidylethanolamine, phosphatidylglycerol, phosphatidylinositol and phosphatidylserine. The quantity of phospholipid coated (in comparison with that initially deposited) on the microtitration plates was precisely evaluated in order to determine if the results (absorbance values) obtained for each phospholipid could be compared directly. The systemic lupus erythematosus sera tested gave positive results for all the phospholipids. The highest level of autoantibodies was observed with phosphatidic acid followed by phosphatidylserine, phosphatidylinositol, cardiolipin, phosphatidylglycerol, phosphatidylcholine and phosphatidylethanolamine. The sera seemed to contain antibodies directed either against all the 8 phospholipids tested or more specifically against one or two phospholipids. The results were compared with those obtained with 17 healthy sera. Much lower values were obtained for the sera of healthy subjects, the majority of which showed a weak binding, similar for all the phospholipids. These results suggest that the anti-phospholipid autoantibodies present in systemic lupus erythematosus sera are significantly higher than those of healthy subjects. It is concluded that in the investigation of anti-phospholipid antibodies, tests should be carried out for all the phospholipids.

Antiphospholipid antibodies and recurrent pregnancy loss: correlation between the activated partial thromboplastin time and antibodies against phosphatidylserine and cardiolipin

Concordance was determined among the presence of the lupus anticoagulant measured by prolongation of the activated partial thromboplastin time and IgG and IgM antibodies against phosphatidylserine and cardiolipin in 47 patients selected for study because of histories of recurrent spontaneous pregnancy loss and a positive test for at least one antiphospholipid antibody. Forty-five of 47 patients (96%) had a prolonged activated partial thromboplastin time, ranging from 46 to 150 seconds. Elevated levels of IgG antiphosphatidylserine antibodies and IgM antiphosphatidylserine antibodies were present in 41 (87%) and in 19 (40%) of samples, respectively. Antibodies against cardiolipin were less commonly observed; IgG anticardiolipin antibodies in only 32 (68%) of 47 samples and IgM anticardiolipin antibodies in 15 (36%) of 42 samples. Neither the level of IgG antiphosphatidylserine antibodies nor the level of IgG anticardiolipin antibodies correlated well with the degree of prolongation of coagulation in the activated partial thromboplastin time (R = 0.312, p = 0.032 for IgG antiphosphatidylserine antibodies versus activated partial thromboplastin time; R = 0.251, p = 0.088 for IgG anticardiolipin antibodies versus activated partial thromboplastin time). Concordance with the activated partial thromboplastin time, however, was observed in 41 (87%) samples for IgG antiphosphatidylserine antibodies and in only 32 (68%) samples for IgG anticardiolipin antibodies. Our conclusion is that the antiphosphatidylserine assay correlates best, although not totally, with the presence of lupus anticoagulant and that the antiphosphatidylserine assay is more sensitive than testing for anticardiolipin.

Phosphatidylserine-induced modulation of the immune response in mice: effect of intravenous administration

The action of phosphatidylserine on the immune response has been examined in mice after the intravenous administration of phospholipid or exposing cultured splenocytes to the action of phosphatidylserine vesicles. Phosphatidylserine (5-25 mg/kg) reduces the T-dependent and the T-independent antibody production. This effect is observed when the phospholipid is injected before (4 h) but not after (24 h) the immunization. The decreased influence of phosphatidylserine injected 24 h before the immunization indicates the reversibility of the action of phospholipid. The effect on the immune system may in part reflect a direct interaction with lymphocytes, since phosphatidylserine (12-60 microM) decreases the production of T-cell growth factors (mainly interleukin-2) elicited by mitogens in cultured spleen cells and reduces the expression of growth factor receptors in the same cells activated by mitogens. In addition, the activity of T-helper cells is found to be reduced in mice receiving the injection of phosphatidylserine. By contrast, the antigen processing and presentation by macrophages is not affected. The data suggest that the intravenous injection of phosphatidylserine vesicles in mice is followed by a transient decrease of lymphocyte activity.

Specific immunocytochemical visualization of phosphatidylserine

In order to determine whether anti-phosphatidylserine antibodies are able to detect phosphatidylserine in situ, an immunocytochemical approach has been developed using human platelets. A strong positive reaction was obtained when anti-phosphatidylserine serum was applied to platelets whereas no reaction was observed with preimmune serum, or with immune serum which had been preincubated with 10(-5) M phosphatidylserine, suggesting that phosphatidylserine was indeed specifically detected by the antibodies.