Lymphocyte autoantibodies and alloantibodies in HIV-positive haemophilia patients.

In order to elucidate the fine specificity of anti-cardiolipin antibodies (ACA) in patients with SLE compared to patients with syphilis (SY) various inhibition experiments were performed. Seven SLE sera and eight SY sera positive for ACA were diluted and preincubated with either cardiolipin VDRL-antigen, mitochondial particles, dsDNA, ssDNA or dilution buffer. The sera were subsequently assayed for residual ACA activity of IgG or IgM class using a sensitive ELISA technique. Significant inhibition of IgM ACA activity in SLE sera was found with cardiolipin, VDRL-antigen and mitochondrial particles. Cardiolipin inhibited binding to a significantly higher extent than the other antigens. In SY sera significant inhibition of the IgM ACA activity was found with all antigens used. The strongest inhibition was seen using VDRL-antigen. Inhibition of IgG ACA activity could only be clearly estimated in SY sera where VDRL-antigen was found to be a much stronger inhibitor than the rest, purified cardiolipin being the weakest. Only two out of seven SLE sera were IgG ACA positive which made a clear conclusion impossible but a strong inhibitory capability of pure cardiolipin and a weaker inhibition with VDRL-antigen was found. This study disclosed a difference between SLE and SY sera showing strong reactivity of ACA in SLE sera with purified cardiolipin, contrasting to ACA in SY sera which predominantly reacted with cardiolipin in the liposome environment, as found in the VDRL-antigen and in mitochondrial particles.     

Anti-mitochondrial type M5 and anti-cardiolipin antibodies in autoimmune disorders: studies on their association and cross-reactivity.

In a series of 42 positive sera, anti-mitochondrial type M5 antibodies (AMA-M5) were found most frequently in patients with SLE (24) and SLE-like syndromes. Patients with AMA-M5 displayed a higher prevalence of thrombocytopenia, thrombosis, biological false positive seroreactions for syphilis, lupus-like anticoagulant activity and anti-cardiolipin antibodies in comparison with a group of 43 SLE AMA-M5 negative patients. The strong association between anti-phospholipid and AMA-M5 antibodies cannot be explained entirely by cross-reactivity between these two groups of antibodies, as indicated by absorption experiments and studies using affinity purified antibody preparations. However, cardiolipin liposomes were able to reduce partially the titres of AMA-M5 sera, suggesting that a small population of AMA-M5 antibodies exists that cross-reacts with cardiolipin. The existence of this population was further substantiated by our demonstration that an IgM monoclonal antibody, from a patient with Waldenström''s macroglobulinaemia, displayed both anti-cardiolipin and AMA-M5 activity, and AMA-M5 activity was completely inhibited by cardiolipin.     

Binding profiles of anticardiolipin antibodies in sera from patients with SLE and infectious diseases.

Inhibition experiments were performed to study the specificity of IgG-class antibody, binding to cardiolipin immobilized onto a polystyrene surface, in sera from patients with systemic lupus erythematosus (SLE) or infection. Six different phospholipids (three anionic: cardiolipin, phosphatidylserine and phosphatidic acid, and three neutral: phosphatidylcholine, phosphatidylethanolamine and platelet activating factor), lipopolysaccharide from Salmonella Minnesota (ReLPS), strain Re595 and lipoteichoic acid from Streptococcus pyogenes were used as inhibitors, in the form of liposomes. Eight of fifteen SLE sera exhibited strong reactivity to phosphatidylserine liposomes; other anionic phospholipids, cardiolipin and phosphatidic acid, were less effective inhibitors. The binding was inhibited effectively only by cardiolipin in three of the SLE sera, and by none of the anionic phospholipids tested in the remaining four SLE sera. In most sera from patients with bacterial infections (including syphilis), anti-cardiolipin antibodies (ACA) were inhibited only by cardiolipin, but in some cases also by phosphatidic acid. In Gram-negative infections, ACA were inhibited by ReLPS more effectively than by cardiolipin. ReLPS also inhibited ACA in two of five chlamydial sera. Appreciable inhibition of ACA by phosphatidylserine did not occur in infections. Thus, in contrast to previous studies, broad reactivity to anionic phospholipids occurred in only about half of SLE sera. This pattern of polyreactivity was not seen in infections.     

Further immunological studies of sera containing anti-mitochondrial antibodies, type M 5.

All of 15 sera containing anti-mitochondrial antibodies (AMA), type M 5, reacted in ELISA with ssDNA, whereas only four had anti-nuclear antibodies as demonstrated by immunofluorescence technique. Twelve of 15 had biological false-positive seroreaction for syphilis and seven of 11 cases investigated had a positive lupus anti-coagulant test. Cold agglutinins were present in 11 sera. Hyper-gamma-globulinaemia was not a prominent finding, but C4 values below the lower limit were common in spite of C3 within the normal range. Absorption of IgG fractions from three different sera with cardiolipin eliminated the reaction with ssDNA and mitochondria, supporting a certain degree of cross-reactivity among the antibodies. The presence of AMA, type M 5, seemed to discriminate a group of patients with symptoms often consistent with SLE although some of the most prominent findings were often absent.     

The effects of incubation temperature and coating procedure on the measurement of antibodies to cardiolipin

Many laboratories have established ELISAs for the the routine detection of anti-cardiolipin antibodies (ACA). Earlier studies had indicated that assay incubation at 37 degrees C may interfere with the antigen binding capacity of these antibodies. We have reexamined this phenomenon by comparing ACA titers obtained when incubations are performed at either 37 degrees C or at room temperature (RT). In addition, the effect of coating antigen in aqueous or organic solution was compared. The sera tested included a set of recognized ACA standards and samples from 19 patients with SLE, two with primary anti-phospholipid syndrome, 71 patients with a variety of autoimmune and non-autoimmune disorders and 210 blood bank controls. The results show that while some sera do perform better under either incubation temperature there was no correlation between ACA titers and incubation temperature on a population basis either for IgG or IgM isotypes. This was seen both for positive standards and patient sera. For IgG ACA a similar phenomenon was seen if the microplates were coated with cardiolipin either in sodium carbonate or ethanol. For IgM ACA there was a significant increase in ACA titers at RT when cardiolipin was coated in ethanol. The data suggest that for most sera neither the antigen coating medium nor the assay incubation temperature are important variables in the determination of IgG ACA. Factors contributing to the influence of either variable in individual sera could not be identified.     

Heterogeneity of binding reactivity to different phospholipids of antibodies from patients with systemic lupus erythematosus (SLE) and with syphilis.

The binding specificities were investigated of anti-phospholipid antibodies derived from sera from 55 patients with SLE and related diseases, and from 33 patients with syphilis. Antibodies from both these groups of patients bind strongly to cardiolipin in solid-phase immunoassays, but only antiphospholipid antibodies from patients with autoimmune diseases are associated with thrombotic complications and recurrent spontaneous abortions. IgG anti-phospholipid antibodies from both groups of patients cross-reacted with a range of negatively charged phospholipids, but binding to neutral phospholipids was largely restricted to sera from patients with syphilis. A monoclonal IgM lambda anti-cardiolipin antibody, derived from a patient with autoimmunity, was used to inhibit binding of anti-phospholipid antibodies to cardiolipin and to phosphatidic acid. This antibody inhibited the binding of autoimmune sera to cardiolipin more strongly than sera from syphilis patients, but the converse pattern of inhibition of binding to phosphatidic acid was observed. The VDRL titre correlated with anti-phospholipid antibody activity in sera from syphilis patients, but not from those with autoimmunity. Lupus anti-coagulant activity correlated weakly with IgG antibody levels to each of the negatively charged phospholipids among the patients with autoimmunity. Lupus anticoagulant activity did not correlate uniquely with any anti-phospholipid antibody specificity. These results provide further documentation of the great heterogeneity of anti-phospholipid antibodies associated with autoimmune disease and syphilis.     

Enzyme-linked immunosorbent assay for detection of antibodies to the venereal disease research laboratory (VDRL) antigen in syphilis.

An enzyme-linked immunosorbent assay (ELISA) for detection of immunoglobulin G (IgG) and IgM to cardiolipin, lecithin, and cholesterol (VDRL [Venereal Disease Research Laboratory] ELISA) is described. The specificity of the VDRL ELISA for IgG and IgM was 99.6 and 99.5%, respectively, with sera from 1,008 persons without syphilis. For a group of patients with false-positive results in traditional nontreponemal tests and for patients with autoimmune diseases, the VDRL ELISA for IgG had a higher specificity than the VDRL ELISA for IgM. The sensitivity for IgG and IgM with 118 sera from patients with untreated syphilis was 96.6 and 94.9%, respectively, which was equivalent to the sensitivities of the traditional nontreponemal tests. The performance of the VDRL ELISA was compared with that of an ELISA that uses cardiolipin as the antigen (cardiolipin ELISA). The VDRL ELISA was significantly more sensitive (P less than or equal to 0.01) than the cardiolipin ELISA with 25 sera from syphilis patients but was less sensitive (P less than or equal to 0.01) with 53 sera from patients with autoimmune diseases. The antibody reactivity in the VDRL ELISA could not be absorbed out by lecithin and cholesterol, and the sera from patients with syphilis did not react in an ELISA that uses cholesterol and lecithin as the antigen. This indicates that cholesterol and lecithin, although not antigenic by themselves, may change the structural form of the epitope on cardiolipin so that it becomes more recognizable for antibodies in syphilis and less recognizable for antibodies in autoimmune diseases. The results of the VDRL ELISA were expressed in percentages of the absorbance value of a positive control. The VDRL ELISA gave, without titration of sera, quantitative results that correlated with the quantitative results of the traditional nontreponemal tests obtained by titration. The VDRL ELISA will be well suited for large-scale testing for syphilis and may replace other nontreponemal tests.     

High prevalence of anti-mitochondrial antibodies among patients with some well-defined connective tissue diseases.

A sensitive enzyme linked immunosorbent assay for determination of low levels of anti-mitochondrial antibodies (AMA) has been developed. With this method, sera from patients with primary biliary cirrhosis (PBC) and patients with different connective tissue diseases were investigated. Ninety percent of PBC sera were found to harbour high levels of AMA and a high proportion of patients with systemic lupus erythematosus (SLE), but also other patients with connective tissue diseases were found to have low affinity or low concentrations of AMA in their sera. AMA positive sera were further investigated with sodium dodecyl sulphate polyacrylamide gel electrophoresis and immunoblotting technique. PBC showed reactivity to 70, 50 and 45 kD mitochondrial polypeptides. SLE sera showed reactivity to 70 and 45 kD polypeptides and furthermore to a 65 kD polypeptide. Many of the AMA positive sera from patients with connective tissue diseases reacted to a 65 kD polypeptide.     

Use of monoclonal antibodies to identify shared idiotypes on anticardiolipin and anti-DNA antibodies in human sera.

Using hybridoma technology we produced monoclonal antibodies (MoAb) to idiotypic determinants on human anti-cardiolipin antibodies purified from a patient with SLE. Hybridomas were screened by inhibition of cardiolipin binding activity of sera from patients with SLE. Seven hybridomas were selected, two of which were studied extensively. Sera from a number of patients with SLE were found to share idiotypic determinants. This cross-reacting idiotype was not detectable on anti-cardiolipin antibodies in syphilis sera. The cross-reacting idiotype was present in sera with anti-ssDNA antibodies even though some of these sera had no anti-cardiolipin antibodies. We propose that these MoAb may recognize a regulatory idiotype.     

Autoantibodies in human chronic graft-versus-host disease after hematopoietic cell transplantation

Primary biliary cirrhosis (PBC) and graft-versus-host disease (GVHD) are thought to have common immunopathologic features and previous studies have reported that 5.2 to 81% of patients with chronic GVHD after allogeneic hematopoietic cell transplant have antimitochondrial antibodies (AMA). We studied a total of 89 patients with chronic GVHD and 60 controls for AMA reactivity by ELISA and immunoblotting using recombinant PDC-E2, BCOADC-E2, and OGDC-E2, immunoblotting of beef heart mitochondrial proteins, and reactivity to nuclei, smooth muscle (ASMA), ribonucleoprotein JO-1, extractable nuclear antigen, nuclear proteins SSA/ SSB, ribonucleic P proteinase III, cardiolipin (ACA), liver kidney microsomal, thyroid microsomal, myeloperoxidase, and the reactivity of rheumatoid factor. A subset of 60 chronic GVHD sera were tested for reactivity to gp210 and LBR. Finally, liver tissue from patients with chronic GVHD and PBC was studied by immunohistochemistry to determine whether there was comparable abnormal apical staining of biliary epithelial cells using PDC-E2-specific monoclonal antibodies. Surprisingly, there were no AMA found in the sera from the 89 patients with chronic GVHD. Review of published data on AMA in GVHD suggests that previous results were primarily false positives. In contrast, sera from the patients with GVHD did have a variety of other autoantibodies and, in particular, 20/89 (22.4%) positive ANA, 23/89 (25.8%) positive ASMA, and 9/89 (10.1%) positive ACA. The other autoantibodies assayed were not statistically different from controls. Finally, abnormal biliary epithelial luminal staining of bile ducts was found, as expected, in liver tissue of patients with PBC but was absent in chronic GVHD.     

Evaluation of the cross-reaction between anti-DNA and anti-cardiolipin antibodies in SLE and experimental animals.

The cross-reaction between anti-DNA and anti-cardiolipin IgG antibodies and its relation to the standard test for syphilis was studied with sera and monoclonal antibodies derived from human patients and mice with systemic lupus erythematosus (SLE). Syphilitic sera of humans and rabbits infected with the spirochete Treponema pallidum were also tested in this study. In addition, rabbits were immunized with ssDNA and cardiolipin and the cross-reactions of the induced antibodies were studied in two different assay systems. The results of these experiments suggest: that the anti-DNA and anti-cardiolipin IgG autoantibodies in SLE sera constitute separate antibody populations and, therefore, cardiolipin cannot play a role in the induction of immune response to DNA in SLE; that in immunized experimental animals there is a significant level of cross-reaction between anti-DNA and anti-cardiolipin-the detection of this cross-reaction depends on highly amplified solid phase assay systems which measure low affinity antibodies and that there is no correlation between the activity of syphilitic sera in the serologic test for syphilis and their binding to pure cardiolipin-this implies that cardiolipin may not be the dominant ingredient in this test as previously proposed.     

Detection of mitochondrial antibodies directed against the primary biliary cirrhosis (M2) antigen by an enzyme-linked immunosorbent assay (ELISA)

An enzyme-linked immunosorbent assay (ELISA) was developed for the detection of 1 subtype of mitochondrial antibodies (AMA) specific for chronic cholestatic inflammatory liver diseases. AMA were detected by ELISA in 16 of 16 patients with primary biliary cirrhosis (PBC) and in 2 of 31 patients with chronic active hepatitis. These 18 positive sera were positive for AMA by indirect immunofluorescence (IF) and by radioimmunoassay (RIA). No AMA were detected by ELISA in 2 patients with the pseudolupus erythematosus syndrome, who were positive for AMA by IF, 2 patients with secondary syphilis, positive for cardiolipin antibodies, 1 patient with systemic lupus erythematosus, positive for AMA by IF, 58 further patients with various hepatic and non-hepatic diseases and 10 healthy blood donors. The titers obtained by ELISA, ranging from 1:20 to 1:62,500, correlated well with those obtained by IF and RIA. The ELISA detected an AMA directed against one determinant of a mitochondrial antigen bearing the characteristics of the so-called PBC antigen (M2 antigen). The ELISA described is a sensitive and specific test for the detection of AMA directed against the PBC (M2) antigen and may be used not only as a standard method assaying this clinically important subtype of AMA but also as a tool for further purification and characterization of the PBC (M2) antigen.     

Measurement of anti-DNA antibodies by ELISA: a comparative study with Crithidia and a Farr assay

One hundred and twenty six sera from 116 patients with systemic lupus erythematosus (SLE) and from 51 control patients were assayed for the presence of anti-DNA antibodies, using a commercial enzyme linked immunosorbent assay (ELISA). Fifty three sera (42%) from SLE patients were positive and a further 13 sera (10%) fell in the 'equivocal' positive range. Three control sera were positive. In a standard 14C DNA Farr assay, 67 sera (53%) from SLE patients were positive. One control serum was weakly positive. There was a good linear correlation between absorption in the ELISA and the 14C DNA binding result (r = 0.73). Results in the ELISA and Farr assays were concordant in 96 of the 126 SLE sera, and 47 of 51 control sera. Sequential sera from a further 6 patients with fluctuating clinical activity of SLE showed similar patterns of change of anti-DNA antibodies in both assays. The ELISA was more sensitive than the Crithidia luciliae immunofluorescence assay which detected 44 positive sera (35%) in the SLE group. These results suggest that this ELISA assay may be a useful alternative to the Crithidia assay or an effective screen prior to testing in the more technically difficult and time consuming Farr assay for the measurement of anti-DNA antibodies.     

The significance of autoantibodies coexisting with anti-centromere antibodies in sera of patients with primary biliary cirrhosis

Anti-centromere antibody (ACA) has been believed to be specific to patients with CREST syndrome, a variant of scleroderma (PSS). This study was undertaken to clarify the distribution of ACA in various diseases and the significance of autoantibodies coexisting with it. The sera of patients with primary biliary cirrhosis (PBC) along with collagen diseases and aged subjects were examined for ACA by immunofluorescence method (IF) using cultured HEp-2 cells and chromosomes prepared from K 562 cells. ACA were found in sera of 10 patients with PBC, one with scleroderma, one with cerebral infarction and one with chronic renal failure respectively. ACA positive sera were examined for antibodies against other nuclear antigens including nRNP, Sm, Scl-70, SS-A and SS-B and cytoplasmic antigens by double immunodiffusion methods using rabbit thymus extract etc. as the antigens and by IF method using cryostat sections of rat kidney and stomach. In 13 sera with ACA, antimitochondrial antibody (AMA), anti-smooth muscle antibody (ASMA) and anti SS-A antibody were found in 10, 4 and one sera respectively. In 10 PBC patients with ACA, various collagen disease-related disorders were found to coexist; CREST syndrome in one, CRST syndrome in one, Raynaud's phenomenon in two and Sj?gren's syndrome in 5. These results would indicate that ACA may be one of the common serological abnormalities among patients with PBC, CREST syndrome and Sj?gren's syndrome.     

Analysis of anti-idiotypic antibodies against anti-microsomal antibodies in patients with thyroid autoimmunity.

Anti-microsomal antibody (AMA) activity was inhibited in 14 of 16 sera and in all 12 IgG preparations from patients with postpartum thyroiditis following incubation with F(ab')2 fragments from normal polyspecific immunoglobulin for therapeutic use (ivIg). Similar results were observed with sera from seven of seven patients with Graves' disease and five of six patients with autoimmune hypothyroidism. Results of these competitive binding assays and affinity chromatography of AMA IgG on Sepharose-bound F(ab'), fragments from ivIg indicated that AMA antibodies reacted with ivIg through idiotypic-anti-idiotypic interactions. Eight out of 10 IgG preparations from patients with autoimmune thyroid disease also showed inhibition of AMA activity when coincubated with autologous IgM at various IgG:IgM molar ratios. These observations suggest that ivIg can inhibit anti-microsomal antibodies through idiotype-anti-idiotype interactions and that such interactions occur with IgM anti-idiotype antibodies in vivo, providing evidence of a role for idiotypic network regulation in the control of thyroid autoimmunity.     

Anti-phospholipid antibodies in HIV infection and SLE with or without anti-phospholipid syndrome: comparisons of phospholipid specificity, avidity and reactivity with beta2-GPI.

Increased prevalence of anti-phospholipid antibodies (aPL) and increased levels of lipid peroxidation have been described in patients with HIV infection. To assess the binding specificity and avidity of aPL antibodies in HIV infection, sera from 44 HIV-1 infected patients were evaluated for antibodies to cardiolipin (aCL), phosphatidyl serine (aPS), phosphatidyl inositol (aPI) and phosphatidyl choline (aPC) using enzyme linked immunosorbent assay (ELISA) methods. Sera from 30 patients with systemic lupus erythematosus (SLE), but without features of anti-phospholipid syndrome (APS) (SLE/non APS), six with SLE and secondary APS, (SLE/APS) and 11 with primary APS (PAPS) were also evaluated as controls. The resistance of the aPL antibody binding to dissociating agents was evaluated by treating the ELISA wells, after serum incubation with 2 M urea or 0.6 M NaCl for 10 min. An anti-beta2-glycoprotein-I (beta2-GPI) ELISA was used to assess serum reactivity against beta2-GPI, a plasma protein considered as the true antigen of aCL antibodies occurring in APS and SLE patients. The prevalence of aCL, aPS, aPI and aPC antibodies in HIV-1 infection was 36%, 56%, 34% and 43% respectively, which was comparable to that found in SLE/APS and PAPS patients and significantly higher than that observed in SLE/non-APS patients. Anti-beta2-GPI antibodies occurred in 5% of HIV-1 infected vs. 17% in SLE/non-APS (P=0.11), 50% in SLE/APS (P=0.009) and 70% in PAPS patients (P=0.0014). A significant decrease of aPL binding after urea and NaCl treatment was observed in the sera of HIV-1-infected, compared to that of APS patients, indicating that aPL antibodies from HIV-1 infected individuals have low resistance to dissociating agents. In conclusion, aPL antibodies (1) occur in HIV-1 infection; (2) tend to recognize various phospholipids but not beta2-GPI; and (3) are of low resistance to dissociating agents-a finding probably reflecting low antibody avidity. Finally, these, like the autoimmune-type aCL antibodies, tend to recognize the oxidized CL-a finding probably indicating autoantibody generation as a result of neoepitope formation by oxidized PLs.     

Measurement of anti-cardiolipin antibodies by an enzyme-linked immunosorbent assay (ELISA): standardization and quantitation of results

We describe the development of a simple and highly sensitive double antibody sandwich enzyme-linked immunosorbent assay (ELISA) for measuring IgG and IgM anticardiolipin antibodies (ACA). Microtitre plates were coated with cardiolipin at a concentration of 45 micrograms/ml by evaporation under nitrogen. Non-specific binding of diluted sera was eliminated by blocking of plates with 10% fetal calf serum in phosphate buffered saline (PBS/FCS) for 2 h. Then sera (100 microliters) at a dilution of 1:100 were incubated in the wells for 1 h. Affinity purified goat anti-human IgG or IgM (100 microliters) at a concentration of 1 microgram/ml was subsequently added and allowed to incubate for 1 h; detection of ACA was achieved using an alkaline phosphatase conjugated rabbit anti-goat IgG reagent by reading the colorimetric yield at 405 nm after incubation with substrate. Reference serum pools were established to study reproducibility of the assay throughout its sensitivity range, and Standard curves were established. The quantitative normal range was 0-9.0 Anticardiolipin ELISA Units (AEU) for IgG and 0-8.0 (AEU) for IgM-ACA. A strong correlation was found between the ELISA and radioimmunoassay methods for measuring ACA of both IgG and IgM classes. Results from 65 patients with systemic lupus erythematosus (SLE) and 45 patients with seropositive rheumatoid arthritis are also reported. The advantages of the ELISA method for quantitative determination of ACA levels, should make it a useful and reliable method for clinical and experimental monitoring of patients with SLE and associated autoimmune disorders.     

Binding affinity of serum immunoglobulin G to cardiolipin and other phospholipids in patients with systemic lupus erythematosus and syphilis.

Qualitative and quantitative assays for human antibodies to cardiolipin and other phospholipids were used in tests for these reactions in sera from patients with systemic lupus erythematosus (SLE) and syphilis. Of 22 SLE serum samples tested by the qualitative assay, 8 showed positive staining to cardiolipin, phosphatidic acid, and/or phosphatidylserine. All 47 syphilitic sera reacted with these three phospholipids. The apparent affinity of anticardiolipin binding was estimated by normalizing absolute binding levels as a function of serum concentration to the maximum percent bound. It was evident that antibody affinity was four- to fivefold lower in the SLE sera than in the syphilitic sera. Twelve serum samples from patients with one or more features of the anti-cardiolipin syndrome demonstrated mean binding values which were not distinguishable from binding in other SLE sera. In sera from patients with active SLE, binding affinity for cardiolipin was somewhat greater than that in samples from patients with inactive disease, but the differences were not statistically significant. The low anticardiolipin binding affinity which was observed in patients with SLE compared with that in patients with syphilis casts doubt on a pathogenic role for these reactions.     

Effective Inhibition of Cardiolipin-Binding Antibodies in Gram-Negative Infections by Bacterial Lipopolysaccharide

Anticardiolipin antibodies (ACA) were detected by solid-phase enzyme immunoassay in the majority of sera from patients with Gram-positive and Gram-negative bacterial infections. The response involved all the major immunoglobulin classes IgG, IgM, and IgA. The specificity of the ACA was studied in competitive inhibition experiments with three putative antigens: cardiolipin, lipopolysaccharide (LPS) isolated from Salmonella minnesota, strain Re 595, and synthetic Escherichia coli lipid A. The binding of IgG class ACA from the sera of five patients with Gram-negative infections was effectively inhibited by LPS, whereas 100-fold more cardiolipin was required for comparable inhibition. Pure lipid A was a less effective inhibitor of anticardiolipin activity than LPS. This pattern of reactivity was not seen in sera from patients with Gram-positive infections, syphilis, or systemic lupus erythematosus. Our findings suggest that cardiolipin may not be the inducing antigen for the cardiolipin-binding antibodies that develop in Gram-negative infections.     

Anti-phospholipid antibodies in syphilis and a thrombotic subset of SLE: distinct profiles of epitope specificity.

In a study of connective tissue and infectious disease sera, we have demonstrated IgM and IgG anti-cardiolipin activity, in a solid phase radioimmunoassay, in systemic lupus erythematosus (SLE), rheumatoid arthritis, syphilis and in acute malaria caused by four different species of Plasmodium. The highest values were noted in SLE (IgM anti-cardiolipin P less than 0.005, IgG anti-cardiolipin P less than 0.01), but there was no correlation with anti-dsDNA, rheumatoid factor or VDRL titres in any disease group. Anti-cardiolipin binding was significantly associated with the lupus anticoagulant, thrombocytopenia, spontaneous abortions and thromboses in the SLE patients. Ten SLE sera from this thrombotic subset and 10 syphilitic sera with similar anti-cardiolipin activity, were tested against four phospholipid antigens and showed significantly different anti-phosphatidyl ethanolamine/anti-phosphatidyl serine binding ratios (P less than 0.001). These differences in phospholipid epitope specificity could explain the specificity of the VDRL antigen in syphilis serology, and we discuss a putative role for anti-phosphatidyl serine in the thrombotic diathesis of SLE.