A DNA antigen that reacts with antisera to cardiolipin

Cross-reactions of anti-DNA antibodies and the central dogma of lupus nephritis

DNA-anti-DNA immune complexes have been implicated in the path1ogenesis of systemic lupus erythematosus (SLE) despite the absence of convincing evidence for the presence of DNA antigen in patients' blood or tissues. Several cross-reactions of anti-DNA antibodies have been described in recentyears. Some of these reactions provide new insights into the mechanisms of tissue injury in SLE. Here Dan Eilat suggests that the target antigen for anti-DNA antibodies may be other than DNA.

Subacute cerebellar ataxia and atrophy developed in a young woman with systemic lupus erythematosus whose cerebrospinal fluid was positive for antineuronal cell antibody

Subacute cerebellar ataxia in combination with cerebellar atrophy has rarely been reported as one of the manifestations of lupus in the central nervous system (CNS). We describe a 27-year-old woman with systemic lupus erythematosus who developed subacute cerebellar ataxia. Computed tomography and magnetic resonance imaging of her brain showed cerebellar atrophy in both hemispheres, particularly on the right side. Moreover, increased antineuronal cell antibody levels were detected in her cerebrospinal fluid. The cerebellar ataxia improved markedly following high-dose corticosteroid administration. This suggests that a relationship exists between autoantibodies and subacute atrophic processes in CNS lupus.

DNA-bound lipids of normal and tumor cells: retrospective and outlooks for functional genomics

By very soft phenol method, the high-molecular-mass natural DNA complexes (10(8)-10(9) Da), which contain 1-3% specific lipids, were isolated from different eukaryotic and prokaryotic cells. Two pools of DNA-bound lipids were isolated: loosely bound (extracted with 35% ethanol) and tightly bound lipids (extracted after additional treatment DNAse I). The composition of these two lipid pools of different sources (rat thymus, liver, regenerating liver, loach sperm, pigeon erythrocytes, Zajdel ascites hepatoma, Ehrlich ascites carcinoma, sarcoma 37, Escherichia coli B, T2 phage) was studied. The DNA-bound lipid pools consist of neutral lipids (NL) and phospholipids (PL), moreover NL is always in a few fold more than PL. The composition of these lipid pools of eukaryotes distinguishes between themselves, mainly, by free cholesterol (minor fraction), cardiolipin (major fraction), and by phosphatidylcholine. Only the tightly bound lipid pool was present in T2 phage DNA. The dramatic redistribution effect between all fractions of NL pools (free and ester cholesterol, free fatty acids, diglycerides) was observed in DNA synthesis phase of cell cycle on the background of the unchanged composition of PL pools. Comparative analysis of DNA-bound lipid pools of normal and cancer cells was carried out. The DNA-bound lipid pools of transformed cells significantly differ from the same normal cells both by PL composition (cardiolipin) and by the presence of additional fractions (mono- and triglycerides) as well. The possible functions of DNA-bound lipid pools, especially of cardiolipin and cholesterol at the attachment of DNA loops to the nuclear matrix, DNA replicon organization, replication, and transcription are discussed.

Specific natural DNA-bound lipids in post-genome era. The lipid conception of chromatin organization

Two pools of DNA-bound lipids were isolated from DNA supramolecular complex (SC-DNA): loosely bound (extracted with 35% ethanol) and tightly bound lipids (extracted after additional treatment DNase I). The compositions of the two lipid pools from different sources (rat thymus, liver, loach sperm, pigeon erythrocytes, Zajdel ascites hepatoma, Ehrlich ascites carcinoma, sarcoma 37, Escherichia coli B and T2 phage) were studied. The possible functions of DNA-bound lipids, especially of cardiolipin and cholesterol, at the attachment of DNA loops to the nuclear matrix, in DNA replicon organization, replication and transcription are discussed.

[Antiphospholipid antibody syndrome]

BACKGROUND

Antiphospholipid antibodies comprise a family of auto-antibodies mainly characterized by the presence of the lupus anticoagulant (LA) and anticardiolipin antibodies (ACA).

CLINICAL APPEARANCE

The antiphospholipid antibody syndrome is defined by the appearance of frequent thromboses, repeated fetal losses and thrombocytopenia. Other clinical manifestations associated with APA include migraine, chorea, hemolytic anemia, heart valve disease, Budd-Chiari syndrome, perpetual pancreatitic episodes, intestinal infarctions, malignant hypertension, livedo reticularis, pre-eclampsia, fetal growth retardation or catastrophic antiphospholipid syndrome. LA and ACA occur in a variety of clinical conditions (secondary antiphospholipid antibody syndrome, SAPS), including other autoimmune disorders, infectious diseases, neoplastic disorders, in association with the use of certain drugs or in otherwise healthy individuals (primary antiphospholipid antibody syndrome, PAPS).

TREATMENT

Patients with thrombosis associated with APA should receive long-term anticoagulation therapy, whereas treatment of asymptomatic patients seems to be not indicated, because only approximately 10% of patients with APA may develop thrombotic complications. In patients with PAPS there is no evidence that the prophylactic administration of immunosuppressive drugs will prevent thromboembolic events.

Characterization of serum anti-phospholipid antibodies in patients with multiple sclerosis

We measured serum antiphospholipid antibodies (aPL) in patients with multiple sclerosis (MS) using enzyme linked immunosorbent assay (ELISA) and examined the correlations between these antibodies and MS. This study included thirty-two patients with clinically definite MS, thirteen patients with other autoimmune neurological diseases excluding collagen diseases (disease control A), eight patients with collagen vascular diseases (disease control B) and twenty-six healthy persons (normal control). In MS group IgG antibody against cardiolipin (CL) was detected in 3 (9%); among them, cofactor (beta 2-glycoprotein I) dependency was shown in 2 but one was cofactor independent. IgM antibody was elevated in 14 of 32 patients (44%) with MS, but cofactor dependency was not determined. However, this was significantly higher in frequency than that of the disease control A (p < 0.01) and normal control (p < 0.01). Results of antibodies against phosphatidylserine were found similar to CL, but antibodies against phosphatidylcholine were in most cases negative. Each of anti-CL IgG antibody purified from four patients with diverse immunological disorders (primary antiphospholipid antibody syndrome, MS, polyarteritis nodosa and systemic lupus erythematosus) had different reactivities against DNA. In addition, the aPL positive group in MS possessed the autoantibodies such as antinuclear antibody at higher rate than the negative group. However, clinically two groups of MS were indistinguishable. The higher incidence of aPL may imply that a broad spectrum of autoantibodies might be produced in MS; some antibodies presumably related directly to MS pathogenesis are yet to be identified.

Composition of immune deposits present in glomeruli of NZB/W F1 mice

This paper describes the results of experiments designed to investigate the composition of immune complexes present, in the form of immune deposits, in glomeruli of NZB/NZW F1 mice. Granular deposits of mouse IgG were present along the glomerular capillary walls of 6- to 12-month-old mice. Disappearance of mouse IgG from glomerular deposits, indicating a dissociation of immune complexes, was observed following incubation of kidney sections with an excess of mouse IgG, mouse Fc fragments, rat IgG, and rat Fc fragments, but not with human and rabbit Cohn fraction-II (FII), DNA, nucleohistone, and PBS. Antinuclear antibody activity in mouse sera or in glomerular eluates was removed by absorption with mouse IgG or mouse Fc fragments, rat IgG or rat Fc fragments, DNA, and nucleo-histone, but not by absorption with human or rabbit FII. These results suggest that the IgG antinuclear antibodies present in the sera and in glomerular deposits possess rheumatoid factor (RF) activity. In other experiments, kidney sections were incubated with various concentrations of pepsin, which digests the Fc portion of the IgG. After digestion, the sections were washed and stained for mouse IgG, IgG F(ab')2, and IgG Fc. At concentration of 10 micrograms/ml, pepsin completely removed IgG and IgG Fc, whereas faint IgG F(ab')2 deposits persisted in glomerular deposits. At the concentration of 1 microgram/ml, deposits of mouse IgG, F(ab')2, and Fc persisted, while F(ab')2 was observed bound to nuclei of glomerular cells. At the pepsin concentration of 0.1 microgram/ml or 0.01 microgram/ml, IgG F(ab')2 was bound to the nuclei of glomerular and tubular cells, indicating that the digestion of the Fc portion of IgG had released F(ab')2 with nuclear reactivity from glomerular deposits. The solubilization of mouse IgG from glomerular immune deposits with mouse IgG and the demonstration that pepsin digestion releases mouse F(ab')2 with nuclear reactivity are consistent with the interpretation that the immune deposits present in glomeruli of NZB/NZW F1 mice contain complexes formed by antinuclear IgG and IgG RF. These two antibodies probably cross-react and form multilayer aggregates which contribute to the formation of immune deposits.

Immunology and clinical importance of antiphospholipid antibodies

Having reviewed the literature on the association of aPL antibodies with clinical manifestations, it is clear that this group of autoantibodies are of considerable importance. The presence of aPL antibodies in some but not all individuals confers a risk of a clinical syndrome characterized by recurrent arterial or venous thrombosis, thrombocytopenia, hemolytic anemia, or positive Coombs' test, and in females, recurrent idiopathic fetal loss. In SLE, the risk is approximately 40%, compared with a risk of 15% in the absence of aPL antibodies. However, only one half of persons possessing these antibodies have SLE, and overall the risk is around 30%. In some circumstances, such as in chlorpromazine or infection-associated aPL antibodies, there appears to be no increased risk. At the other end of the spectrum are seen patients whose only clinical manifestations comprise features of this clinical syndrome, and this entity has been designated the primary antiphospholipid syndrome (PAPS). aPL antibodies are also important because they are not uncommon. They have been found frequently in women with idiopathic recurrent fetal loss (30%), in non-autoimmune patients with ischemic heart disease (20%), or venous thrombosis (up to 30%), or stroke (4-47%), and in chronic immune thrombocytopenia (30%). These autoantibodies can be detected using sensitive solid-phase immunoassays employing the CL antigen, or in appropriate coagulation tests to detect LA activity. These assays are simple to perform but require care in selection of the best test and in interpretation of results. Current tests do not distinguish between those persons at risk of the clinical events and those not at risk. Detection of specific isotypes (especially IgG) and antibody level may aid in such a designation. Treatment of aPL antibody-associated syndromes remains a controversial subject. Since thromboses are associated with significant morbidity and potential mortality, there is a good argument for long-term preventive antithrombotic therapy, at least for as long as the antibodies are detectable, in those patients in whom clinical complications have previously occurred. It is not generally recommended that this treatment be offered to individuals in whom aPL antibodies are detected but who have not suffered previous thromboses, since the risk of such events does not appear to be equal within a group of aPL antibody-positive persons. This particularly applies to pregnant women, since live births and uncomplicated pregnancies are observed regularly in the presence of aPL antibodies without specific treatment. A previous history of at least one unexplained, late fetal loss is considered a prerequisite before intervention in subsequent pregnancies.(ABSTRACT TRUNCATED AT 400 WORDS)

Anti-DNA antibodies induced by BK virus inoculations. Demonstration of the specificities for eukaryotic dsDNA and synthetic polynucleotides

The ability of BK virus to induce anti-DNA antibodies in rabbits, and the ability of these antibodies to bind natural eukaryotic DNA and synthetic polynucleotides have been analysed. The specificity of the binding was assayed by inhibition of anti-dsDNA and -ssDNA ELISA tests with dsDNA, ssDNA, and synthetic single-stranded as well as double-stranded polynucleotides. The anti-dsDNA activity of two rabbit antisera was effectively inhibited by dsDNA and ssDNA and poly(dAdT)-poly(dAdT). The other nucleotide antigens produced relatively less inhibition. The anti-ssDNA binding was most efficiently inhibited by the homologous antigen, whereas inhibition by dsDNA only reached approximately 70% of the maximum as defined by ssDNA as inhibitor. This indicates the existence of a selective anti-ssDNA antibody population and a population recognizing both ssDNA and dsDNA within the sera. Cross-reaction of the induced anti-DNA antibodies with phospholipid antigens, such as cardiolipin, phosphatidylic acid, and bacterial cell surface, could not be demonstrated. We conclude that antibodies resulting from inoculation with BK virus specifically bind to dsDNA and ssDNA and possess a high affinity for the synthetic duplex poly(dAdT). In this way, they have some similarities with anti-DNA antibodies encountered in SLE (systemic lupus erythematosus) in both man and mouse.

BK virus terminates tolerance to dsDNA and histone antigens in vivo

In order to characterize the immune response to BK virus, a human polyomavirus containing dsDNA and host cell histones, we followed the appearance of antibodies in five outbred rabbits after intravenous inoculation with purified infectious BK virus without any adjuvant. The animals were followed for 15 weeks after the first inoculation and booster doses were given after four and eight weeks. Antibodies were studied by ELISA techniques with the BK virus particle, dsDNA, ssDNA or the individual histones as test antigens. Antibodies to BK virus structural proteins were detected in all rabbits. Two out of five rabbits produced antibodies to dsDNA, ssDNA, nucleosomes and histones H1 and H3. Even a weak reactivity to H2B was detected in one serum. The autoantibody response was transient as it declined after a few weeks, but it reappeared after a second boost in one of the rabbits. The other animals did not respond in the same manner. The specificity of the antibodies against dsDNA was ascertained by inhibition studies employing S1 nuclease treated DNA as inhibitor. Furthermore, the dsDNA used as coating antigen was not recognized by a human reference serum with known specificity for ssDNA. The rabbit antisera did not show any reactivity to a panel of other (in this context irrelevant) autoantigens. This suggests that the anti-DNA and -histone antibodies are not a result of non-specific polyclonal B cell activation. Thus, inoculation of dsDNA viruses may represent a new model that allows us to investigate mechanisms responsible for circumvention of tolerance to self molecules.

Cross-reactions of nucleic acids with monoclonal antibodies to phosphatidylinositol phosphate and cholesterol

Four monoclonal IgM antibodies to phosphatidylinositol phosphate (PIP), four antibodies to cholesterol and one antibody to liposomes containing phosphatidylcholine, cholesterol and dicetyl phosphate were tested for reactivity with denatured DNA. Three of four antibodies to PIP cross-reacted strongly with denatured DNA. The other antibodies did react with denatured DNA but only very weakly. The binding to DNA was competed by synthetic polynucleotides. In competitive assays, one of the anti-PIP antibodies was particularly reactive with poly(dT) and another with poly(I) and poly(dG). Binding of an anti-cholesterol antibody to ssDNA was also inhibited by poly(I) and poly(dG). Two of the anti-PIP antibodies were also reactive with mononucleotides, and all four bound inositol hexaphosphate. High concns of nucleosides did not compete for binding, indicating that phosphate is involved in the binding site. Phospholipids, particularly those containing inositol phosphate, also competed for binding to DNA, but to varying extents, indicating a variable overlap in the antibody binding site for DNA and phospholipid determinants. These antibodies, induced by immunization with liposomes, showed cross-reactivity characteristics often found with certain types of autoantibodies, but they did not bear the H130 idiotype, which was identified on IgM anti-DNA autoantibodies from MRL-lpr/lpr mice.

Immunochemistry of DNA

Since the first reports of anti-DNA antibodies in sera of patients with systemic lupus erythematosus (SLE) in 1957, studies of nucleic acid immunochemistry have grown in two directions. One has been the analysis of the specificity, the nature and the origins of these autoantibodies. The second has been exploration of anti-nucleic acid antibodies that can be induced experimentally, their specificities, and their application as biochemical reagents. Although the properties of autoantibodies and experimentally induced antibodies differ in certain respects, these two lines of research are complementary and provide important information for each other. For example, the production of autoantibodies by adjuvant-stimulated B cells yields a background that has to be considered in evaluating the specificity of weak responses to experimental nucleic acid immunogens: in turn, the possibilities and limitations of experimental immunization should be considered in evaluating possible stimuli for autoantibody production. Several aspects of nucleic acid immunochemistry have been described and evaluated in previous reviews. Following some general statements of historical perspective, this review will emphasize questions addressed and findings of about the last five years.

Cerebellar ataxia in systemic lupus erythematosus: three case reports

Three patients presented with cerebellar ataxia among 350 cases of systemic lupus erythematosus (SLE) seen over the last 14 years. Cerebellar signs were unilateral in one and bilateral in the other two patients. Other neurological findings were present in all three patients. One initially presented with only cerebellar ataxia; other features of SLE appeared a few years later. Lupus anticoagulant test was positive in one patient. Corticosteroids given in the early stages appeared to benefit these patients by ameliorating cerebellar dysfunction.

Is anticardiolipin activity a cross-reaction of anti-DNA or a separate entity?

Putative cross-reactions between anti-DNA and anticardiolipin activities were studied using sera of different patients and a panel of monoclonal antibodies to DNA. Sera were obtained from patients with systemic lupus erythematosus, from patients with syphilis, and from heroin addicts who showed a biologic false-positive result on the serologic test for syphilis. While the patients with syphilis and the heroin addicts had elevated levels of anticardiolipin antibodies in their circulation, no reactivity with DNA was observed in these sera. Sera from systemic lupus erythematosus patients often showed both anti-DNA and anticardiolipin activity. Although a correlation between anti-DNA and anticardiolipin titers was found, this did not always result from cross-reactivity of the same population of antibodies. In fact, we observed a relationship between cross-reactivity and antibody avidity. Anti-DNA of high avidity to DNA showed little cross-reactivity with cardiolipin. Anticardiolipin activity in such sera was based on the presence of specific anticardiolipin antibodies. Anti-DNA of low avidity was found to cross-react with cardiolipin. Among monoclonal antibodies to DNA, we found that cross-reactions with cardiolipin were rare: only 6 of 55 anti-DNA clones produced antibodies that also reacted with cardiolipin.

Cutaneous manifestations associated with the presence of the lupus anticoagulant. A report of two cases and a review of the literature

Two patients with the lupus anticoagulant exhibited unusual cutaneous manifestations. They both fulfilled four criteria for systemic lupus erythematosus and had experienced deep venous thrombosis. The first patient suffered from a leg ulcer that resembled a pyoderma gangrenosum. The second patient presented erythematous and purplish macules on the fingertips. The histologic studies showed only microthrombosis in the dermal vessels without vasculitis, although such lesions in systemic lupus erythematosus are usually attributed to vasculitis. The association of these cutaneous lesions with lupus anticoagulant has never been reported. It is likely that this association is not fortuitous. After a review of the literature, it seems possible to individualize a new syndrome characterized by the presence of a subgroup of antiphospholipid antibodies. Thrombosis, spontaneous abortions, neurologic manifestations, pulmonary hypertension, positive results of a Coombs' test, and thrombocytopenia can be included in this syndrome, which overlaps with systemic lupus erythematosus. Certain cutaneous symptoms are associated with the presence of lupus anticoagulant or other antiphospholipid antibodies: leg ulcers, distal cutaneous ischemia, widespread cutaneous necrosis, and livedo. They can be considered as the dermatologic manifestations of this syndrome.

Antibodies to liposomes, phospholipids and phosphate esters

Polyclonal and monoclonal antibodies to liposomes having various phospholipid compositions have been produced. Binding of the anti-lipid bilayer antibodies is influenced both by the chemical composition and the physical state of the liposomal lipids. The antibodies to liposomes have a 'subsite' in the binding site that recognizes small soluble phosphorylated haptens such as nucleotides (e.g., ATP). The capacity of anti-liposome antibodies to bind to phosphate is also shared by antibodies to numerous other substances, including lipid A from Gram-negative bacterial lipopolysaccharide, cardiolipin, DNA, polynucleotides, and lipoteichoic acids from Gram-positive bacteria. Because of similarities of chemical structures between all of these molecules widespread immunological cross-reactivities are observed.

Evaluation of anti-cardiolipin antibody and its cross-reactivity in sera of patients with lepromatous leprosy

Using a sensitive and modified solid-phase radioimmunoassay for detecting anti-cardiolipin antibodies, sera of 45 patients with lepromatous leprosy were examined. Nine of the 45 (20%) showed positive levels of anti-cardiolipin antibodies. Inhibition tests revealed that these antibodies significantly cross-reacted with double-stranded (ds) DNA, but not with single-stranded (ss) DNA or extractable nuclear antigens (ENA). We describe the unique pattern of antibody cross-reactivity with cardiolipin and dsDNA in sera of patients with lepromatous leprosy.

Antibodies to DNA

Antibodies that recognize specific conformational variations of DNA structure provide sensitive reagents for testing the extent to which such conformational heterogeneity occurs in nature. A most dramatic recent example has been the development and application of antibodies to left-handed Z-DNA. They provided the first identification of Z-DNA in fixed nuclei and chromosomes, and of DNA sequences that form Z-DNA under the influence of supercoiling. Antibodies have also been induced by chemically modified DNA and by synthetic polydeoxyribonucleotides that differ from the average B-DNA structure. These antibodies recognize only the features that differ from native DNA. In most experiments, native DNA itself is not immunogenic. Antibodies that do react with native DNA occur in sera of patients with autoimmune disease, but even monoclonal anti-DNA autoantibodies usually react with other polynucleotides as well. Anti-DNA antibodies, especially those of monoclonal origin, provide a model for the study of protein-nucleic acid recognition.

Immunization of rabbits with purified RNA polymerase I induces a distinct population of antibodies against nucleic acids as well as anti-RNA polymerase I antibodies, both characteristic of systemic lupus erythematosus

Rabbits were immunized with either RNA polymerase I or poly(A) polymerase that had been purified to apparent homogeneity and was devoid of nucleic acids. Sera from rabbits thus immunized were screened for antibodies against nucleic acids. All seven rabbits injected with RNA polymerase I but none of the four rabbits immunized with poly(A) polymerase produced anti-nucleic acid antibodies. Anti-RNA polymerase I antibodies were induced after a single injection of the enzyme. Anti-polynucleotide antibodies were not detectable until after the second immunization. Anti-RNA polymerase I antibodies could be detected with as little as 100 pg of purified RNA polymerase I in the radioimmunoassay. At least 50 ng of poly(A) or 200 ng of DNA was required to detect anti-nucleic acid antibodies. The immunoreactivity of anti-RNA polymerase I antisera was greater with synthetic polynucleotides than with DNA, particularly early in the immunization schedule. Alkaline phosphatase treatment of poly(A) to remove 5' phosphates nearly abolished its antigenicity with respect to the early sera and decreased antibody binding of later sera by 60%. These results indicate that the anti-nucleic acid antibodies produced early were primarily directed against determinants including the 5'-terminal phosphates while antibodies produced later were directed against other sites. The antinucleic acid antibodies and anti-RNA polymerase I antibodies formed two distinct populations that were not immunologically crossreactive. We suggest that after injection, RNA polymerase I becomes associated with the nucleic acids present in blood plasma which renders them immunogenic; thus, association of nucleic acids with autoimmunogenic RNA polymerase I may be one of the mechanisms by which anti-DNA antibodies are induced in systemic lupus erythematosus.

The lupus anticoagulant. A disease marker in antinuclear antibody negative lupus that is cross-reactive with autoantibodies to double-stranded DNA

The lupus anticoagulant (LA) was demonstrated in 37% of 52 consecutive systemic lupus erythematosus (SLE) patients and patients with lupus-like syndromes, who were referred to our unit. The LA was found to be associated with a biologic false-positive VDRL (P less than 0.005), and the apparently paradoxical association of LA with vascular thromboses was confirmed (P less than 0.05). The presence of LA and a biologic false-positive VDRL defined a group of 7 antinuclear antibody negative patients with characteristic features of recurrent thromboses, spontaneous abortions, neurologic involvement, and renal disease. Further studies on 6 selected sera demonstrated LA in all 6 IgM fractions and in 3 of 6 IgG fractions. Inhibition of LA was shown in 6 of 9 Ig fractions after absorption with double-stranded DNA (dsDNA). Anticardiolipin antibody was shown by immunodiffusion in 3 LA positive IgG fractions from VDRL negative sera. Cardiolipin micelles partially inhibited anti-dsDNA binding of 4 IgG fractions, 3 of which were LA negative. In this report we discuss the overlapping specificities due to cross-reactivity between LA, anticardiolipin, and anti-dsDNA antibodies in human SLE, and we suggest that LA be considered equivalent to the biologic false-positive VDRL as a criterion for the diagnosis of SLE.

Analysis of serum binding to DNA and other ligands in systemic lupus erythematosus

Using a solid-phase immunoassay (ELISA), serum binding to dsDNA, cardiolipin, beta 2-microglobulin (beta 2m) and Keyhole limpet haemocyanin (KLH) has been investigated in patients with systemic lupus erythematosus (SLE). Serum binding to DNA, cardiolipin and beta 2m was significantly increased in SLE sera, compared with normal sera; in addition, serum binding to KLH was also significantly increased. There were, however, no significant correlations between serum binding indices to DNA, beta 2m, cardiolipin or KLH; furthermore, in inhibition experiments no clear cross-reactions of lupus sera for these four ligands were detected. These data indicate that SLE sera bind to DNA, as well as to other apparently diverse ligands. Increased serum binding to these ligands may be attributable to a particular characteristic of the immunoglobulin molecules--or groups of immunoglobulin molecules - produced in these patients.

Phosphate-binding specificities of monoclonal antibodies against phosphoinositides in liposomes

Monoclonal antibodies against phosphatidylinositol phosphate were produced after injecting a mouse with liposomes containing dimyristoylphosphatidylcholine, cholesterol, phosphatidylinositol phosphate and lipid A. The antibodies raised were IgM (kappa) and their activities were assayed by complement-dependent damage to liposomes lacking lipid A but containing the rest of original immunizing mixture of lipids. Three of the four antibodies selected cross-reacted with liposomes containing phosphatidylinositol instead of phosphatidylinositol phosphate; and two of the antibodies cross-reacted with liposomes containing phosphatidylinositol diphosphate. Each of the antibodies had a phosphate-binding specificity. Each also cross-reacted with liposomes containing sulfogalactosyl ceramide, but not with liposomes containing galactosyl ceramide, or gangliosides or with liposomes containing lipid A but lacking phosphoinositides. Recognition of sulfogalactosyl ceramide probably occurred because the chemical characteristics of the sulfate group were sufficiently similar to those of phosphate to allow recognition by the antibody. The phosphate-binding specificity was further confirmed by inhibition by phosphocholine, inositol hexaphosphate, ATP, AMP and even sodium phosphate, but not by choline or inositol.

Monoclonal anti-cardiolipin antibodies bind to DNA

BALB/c mice immunized with the phospholipid, cardiolipin, produced anti-cardiolipin and anti-DNA antibodies. Seven hybridomas derived from spleen cells of the cardiolipin-immunized mice produced cardiolipin-binding monoclonal antibodies that also bound to the polynucleotides DNA, poly(dT), and poly(I). The seven cardiolipin-induced monoclonal antibodies shared idiotypic determinants with a high frequency idiotypic marker of spontaneously expressed anti-DNA autoantibodies of lupus-prone MRL-lpr/lpr mice. The monoclonal antibodies presumably bound to phosphodiester phosphate groups that occur in both polynucleotides and phospholipids. The results imply that production of anti-DNA autoantibodies does not require immunization by DNA.

Polyspecific monoclonal lupus autoantibodies reactive with both polynucleotides and phospholipids

Hybridomas the produce anti-DNA autoantibodies were prepared from spleen cells of unimmunized MRL/1 mice, a strain that spontaneously develops severe systemic lupus erythematous (SLE). Reactivities of these monoclonal antibodies with a wide range of polynucleotides prompted tests of their reactions with phospholipids which, like polynucleotides, contain diester-linked phosphate groups in their backbones. In competitive radioimmunoassays, cardiolipin, phosphatidic acid, and phosphatidyl glycerol blocked the binding of these hybridoma antibodies to denatured DNA. These phospholipids also specifically inhibited the reaction between a hybridoma antibody and a site-specific anti-idiotypic antibody. The antinuclear reaction of one of these antibodies was specifically inhibited by cardiolipin. This same antibody prolonged the activated partial thromboplastin time in a manner characteristic of a lupus anticoagulant, presumably by binding to phospholipid in the test system. The polyspecific reactivity of a single molecular species of lupus autoantibody suggests that some of the diverse serological abnormalities of SLE may be a result of the binding of certain autoantibodies to a phosphodiester-containing epitope that is present in diverse biological molecules.

Antibodies to Acholeplasma laidlawii membrane lipids in normal guinea pig serum

Acholeplasma laidlawii is killed and lysed by fresh normal guinea pig serum (GPS) without additional antibodies. Prior incubation of GPS with whole A. laidlawii organisms abolishes the killing activity of GPS. In the present study it was demonstrated that antibodies are present in normal GPS. The classical pathway, not the alternative pathway, of the complement sequence was activated by these antibodies in fresh normal GPS. The antibodies in GPS belong to the IgG class of immunoglobulins. They are directed predominantly against the membrane phospholipids of A. laidlawii. These antibodies may be induced either by natural infection of guinea pigs with A. laidlawii or by antigenic determinants of other microorganisms of food antigens.