Studies on autoantibodies to poly (adenosine diphosphate-ribose) in SLE and other autoimmune diseases

Poly(ADP-ribose) polymerase activity in systemic lupus erythematosus and systemic sclerosis

The aim of this study is to investigate the role of poly(ADP-ribose) polymerase (PARP), involved in DNA repair and in autoimmune pathologic conditions such as systemic lupus erythematosus (SLE) and both limited systemic sclerosis (lSSc) and diffuse systemic sclerosis (dSSc), to assess its possible implication in the pathogenetic processes. The relationship between PARP activity and the intracellular concentration of its substrate nicotinamide adenine dinucleotide (NAD) is also investigated. Peripheral mononuclear cells (PMC) from controls and patients with SLE, lSSc, and dSSc were irradiated with ultraviolet light (UV) and PARP activity was assayed by a radiochemical method. Pyridine nucleotide concentrations were assayed by a high-performance liquid chromatography-linked method. PARP activity was detectable in nonirradiated cells and showed similar values in all groups. The activity significantly increased after UV irradiation in control, SLE, and lSSc cells, but not in dSSc cells. Irradiated PMC from both SLE and dSSc showed lower enzyme activity with respect to irradiated controls. Higher intracellular NAD content was found in all of the pathologic conditions in comparison to values in the control; this difference was statistically significant in dSSc. Our data demonstrate a lower PARP activity in response to UV damage in PMC from patients affected by the above pathologic conditions compared with controls. An inverse relationship between PARP activity and NAD content was also observed.

[The apoptosis marker enzyme poly-(ADP-ribose) polymerase (PARP) in systemic lupus erythematosus]

The enzyme poly-(ADP-ribose) polymerase (PARP) is localized within the cell nucleus and catalyzes DNA-repair. During programmed cell death (apoptosis), PARP is enzymatically cleaved. Detection of the cleavage products is characteristic for apoptosis. In patients with systemic lupus erythematosus (SLE), the highly ordered signal transduction cascade of apoptosis is disturbed. SLE patients show reduced PARP activity . PARP cleavage products are mainly found in association with either antinuclear and/or anti-dsDNA antibodies. In addition, serum samples from SLE patients and other autoimmune diseases display anti-PAR and anti-PARP autoantibodies.

Anti-dsDNA antibodies: still a useful criterion for patients with systemic lupus erythematosus?

The presence of antibodies to dsDNA has been a criterion for systemic lupus erythematosus (SLE) in each of three attempts to classify the disease that have been undertaken by the American College of Rheumatology. The generally good specificity of the test, the fact that it is widely available and often undertaken by an enzyme linked immunosorbent assay (ELISA) which is relatively cheap and easy to perform have encouraged its continued presence in the list of lupus criteria. The detection of anti-dsDNA antibodies is not, however, straightforward and the real significance of the presence of these antibodies, their true specificity (or otherwise), the question of whether they are truly linked to disease pathogenicity and how accurately they reflect disease activity are all questions that have been posed in the past 20 years.

Autoantibody explosion in systemic lupus erythematosus: more than 100 different antibodies found in SLE patients

OBJECTIVE

Description of the various autoantibodies that can be detected in patients with systemic lupus erythematosus (SLE).

METHODS

A literature review, using the terms "autoantibody" and "systemic lupus erythematosus", was conducted to search for articles on autoantibodies in SLE, their target antigens, association with disease activity, or other clinical associations.

RESULTS

One hundred sixteen autoantibodies were described in SLE patients. These include autoantibodies that target nuclear antigens, cytoplasmic antigens, cell membrane antigens, phospholipid-associated antigens, blood cells, endothelial cells, and nervous system antigens, plasma proteins, matrix proteins, and miscellaneous antigens. The target of autoantibody, the autoantigen properties, autoantibody frequencies in SLE, as well as clinical associations, and correlation with disease activity are described for all 116 autoantibodies.

CONCLUSIONS

SLE is the autoimmune disease with the largest number of detectable autoantibodies. Their production could be antigen-driven, the result of polyclonal B cell activation, impaired apoptotic pathways, or the outcome of idiotypic network dysregulation.

Anti-DNA antibodies--overview of assays and clinical correlations

Many authors have studied the links between levels of anti-dsDNA antibodies and disease activity in patients with SLE. Interpretation of these studies must take into account the facts that there are a range of possible assays for anti-dsDNA and a number of indices available for assessing disease activity. A recent study compared levels of various autoantibodies with organ specific disease activity assessed during the British Isles Lupus Assessment Group (BILAG) index. Anti-dsDNA and anti-heparan sulphate levels were more likely to be raised in patients with renal than non-renal disease. Some anti-DNA antibodies are actually anti-nucleosome antibodies, which lose DNA reactivity when purified under dissociating conditions. Patients with SLE have significantly increased levels of nucleosomes in their sera compared with healthy controls. In patients with SLE, reduced clearance of nucleosomes released from apoptotic cells may induce the formation of anti-nucleosome antibodies.

Biochemical characterization of ADP-ribose polymer metabolism in SLE

The metabolism of poly(ADP-ribose) in peripheral blood mononuclear (PBM) cells was studied in 13 patients with systemic lupus erythematosus (SLE) and in 12 age and sex matched controls. Poly(ADP-ribose) polymerase activity was measured as the net accumulation of ADP-ribose polymers during the conversion of 32P-NAD to poly(ADP-ribose) in PBM cells in vitro. The control population showed a mean activity of 418 +/- 91(s.d.)pmol ADP-ribose/10 min/10(6) cells. The SLE population was more heterogeneous and showed a lower mean of 225 +/- 147(s.d.)pmol ADP-ribose/10 min/10(6) cells. The mechanism of decreased ADP-ribose polymer accumulation was investigated. Measurements of turnover of the ADP-ribose polymers and its substrate, NAD+, showed that diminished ADP-ribose polymer accumulation in SLE subjects resulted from decreased poly(ADP-ribose) synthesis and not from altered rates of polymer turnover or NAD utilization. Western blot analyses of enzyme protein levels, kinetic studies of poly(ADP-ribose) polymerase activity and analyses of polymer size distribution suggested that the mechanisms of poly(ADP-ribose) synthesis in SLE cells is not altered but that the number of active poly(ADP-ribose) polymerase molecules is reduced.

New Zealand white rabbits immunized with RNA-complexed total histones develop an autoimmune-like response

The antibody response of rabbits immunized with a total histone mixture containing randomly coiled H1/H5, H2A, H2B, H3 and H4 devoid of DNA was investigated in direct and competitive ELISA. The antisera were tested with isolated histones and chromatin and with a series of overlapping synthetic peptides covering the entire sequences of the four core histones and two peptides of H1. It was found that the New Zealand (NZ) white rabbits immunized with the total histone (TH) mixture complexed with RNA produced IgG antibodies reacting with histones and with a number of histone peptides but not with chromatin. The antisera also contained IgG antibodies which bound components that correspond to common target antigens in autoimmune diseases such as native dsDNA, peptides of Sm-D antigen, ubiquitin, branched peptides of ubiquitinated H2A and poly(ADP-ribose). By competition experiments, it was shown that these antibodies corresponded to non-crossreacting antibody populations. New Zealand rabbits immunized with TH in the absence of RNA or random outbred rabbits immunized with the RNA-complexed histone fraction produced antibodies reacting with histone, chromatin and very few histone peptides, while no activity with non-related antigens was observed. The pattern of reactivity of antisera raised in NZ rabbits with RNA-complexed TH was found to be very similar to that observed in sera of patients with systemic lupus erythematosus while, in contrast, the antibody response was very different in NZ or outbred rabbits immunized with various native nuclear particles and with individual histones. Altered nucleosome particles rather than native nucleosomes may represent the antigenic stimulus giving rise to autoantibodies.

Correlation between clinical features of systemic lupus erythematosus and levels of antihistone antibodies of the IgG, IgA, and IgM isotypes

An attempt was made to define the correlation between the clinical features of systemic lupus erythematosus and levels of circulating antihistone antibodies of the IgG, IgA, and IgM isotypes. Serum antibody levels were determined by enzyme linked immunosorbent assay (ELISA) on serial blood samples (n = 4) from 25 patients, representing five subgroups: (a) renal disease; (b) central nervous system disorders; (c) skin and joint disease only; (d) serositis; and (e) deep venous thrombosis with or without spontaneous abortion. The levels of antihistone antibodies of each isotype varied widely from patient to patient, but antibody levels in the four samples from each patient correlated closely. A close correlation between levels of IgG and IgA antihistone antibodies was found but there was no correlation between these isotypes and IgM antihistone antibodies. In individual patients no simple correlation between disease activity and antihistone antibody levels was established, but levels of antihistone antibodies of the IgG and IgA isotypes were significantly higher in those patients in whom the disease was consistently more active.

Serological and histological characterization of the new mutant strain of lpr mice, CBA/KlJms-lprcg/lprcg

CBA/KlJms-lprcg/lprcg mice with a novel mutation producing systemic lymphoproliferation were investigated for their serological and histological characteristics. The mutant mice showed elevated levels of serum immunoglobulin, C1q-binding immune complexes and antibodies to nuclear antigens such as dsDNA and ssDNA and poly(ADP-ribose). In contrast, histopathological lesions, e.g. glomerulonephritis, vasculitis or interstitial pneumonitis, were not revealed by histological and immunofluorescent examinations, except for lymphocytic infiltration in various organs. These results suggest that this mutant mouse strain may provide a new animal model for autoimmunity. However, further investigations are required to clarify whether this strain is unique as compared with other well-known lupus-prone strains of mice with respect to serological and histological abnormalities and become to be a new model of systemic autoimmune disease.

Disease specificity of antibodies to poly (ADP-ribose); their relationships to anti-DNA antibodies and to disease activity in lupus

In this study we have measured the level of anti poly (ADP-ribose) antibodies in the sera of a number of patients with SLE and their relatives, patients with a wide variety of other autoimmune and infectious diseases, and a group of normal healthy controls. It was found that these antibodies were not disease specific but were present in nine out of thirteen groups tested in significant numbers. The levels of anti poly (ADP-ribose) antibodies and anti DNA antibodies in SLE patients bled serially were also measured. The level of these antibodies fluctuated in parallel in many of these patients, although the anti poly (ADP-ribose) antibodies reflected disease activity more accurately in some.

Presence of antibodies to ubiquitin during the autoimmune response associated with systemic lupus erythematosus

Sera from patients with systemic lupus erythematosus (SLE) were shown to react with both ubiquitin and a synthetic fragment of it (residues 22-45) in an ELISA and with ubiquitin in immunoblotting experiments. Close to 80% of lupus patients possessed ubiquitin antibodies, whereas only 55% of them possessed native DNA antibodies, a marker of SLE. Less than 16% of patients with other rheumatic autoimmune diseases possessed antibodies to ubiquitin. Our results indicate that the combined measurement of antibodies to native DNA and to ubiquitin could appreciably increase the detection of SLE cases (up to 85% in our study). It is suggested that ubiquitin, a heat shock protein, could be involved in antibody formation against ubiquitin-protein conjugates present during cellular injury and that this represents a major characteristic of the autoimmune response in SLE.

Antibody to poly(ADP-ribose) as a predictor of obstetric complications in autoimmune MRL/Mp-lpr/lpr mice: basis for its application to pregnant patients with systemic lupus erythematosus

In pregnant autoimmune MRL/Mp-lpr/lpr (MRL/l) mice with many fetuses the level of anti-poly(ADP-ribose) antibodies was found to be the same as that of age-matched non-pregnant female mice, whereas in mice with few fetuses the level of anti-poly(ADP-ribose) antibodies was high in the early period of pregnancy and rapidly returned to control level at puerperium. The anti-poly(ADP-ribose) antibody that increased during pregnancy seemed to be mono-specific for its antigen, whereas the antibody that increased with age was polyspecific. The isotype/subclass of the former was mainly IgG2a. The marked increase in anti-poly(ADP-ribose) antibodies in the early period of pregnancy suggests endogenous sensitization to poly(ADP-ribose), which may be synthesized abnormally or stored during pregnancy, and is a predictive sign in pregnant lupus mice of a low litter size. This finding is applicable to pregnant patients with systemic lupus erythematosus (SLE); that is, it is a predictive sign of fetal loss and/or maternal risk. This was confirmed in the human cases examined so far.

Human monoclonal antibodies to phenolic glycolipid-1 from leprosy patients cross react with poly(ADP-ribose), polynucleotides and tissue bound antigens

Antibodies which bind to poly(ADP-ribose) have been described in Systemic Lupus Erythematosus (SLE) and a variety of infectious diseases. Two IgM kappa human monoclonal antibodies (MAbs), TH3 and PR4, produced from the fusion of peripheral blood lymphocytes of leprosy patients with the GM4672 lymphoblastoid cell line, were found to bind to poly(ADP-ribose) in direct binding and inhibition ELISAs. Significant inhibition of binding of these MAbs to poly(ADP-ribose) occurred with phenolic glycolipid-1, the M. leprae specific glycolipid, ssDNA, dsDNA, poly(dT), as well as poly(ADP-ribose) itself. Up to 80% of binding of TH3, and 90% of binding of PR4, to poly(ADP-ribose) was inhibited by 10 mcg of ssDNA suggesting that there may be sharing of some conformational determinants. Although the serological binding profiles of TH3 and PR4 are similar, only PR4 was found to bind to basal keratinocytes of normal human interfollicular epidermis and astrocyte cytoplasm in normal brain tissue. These results support the concept that an antibody binding site may accommodate more than one epitope. Furthermore, small differences in antigen binding potential may distinguish relatively innocuous antibodies from those which may be more pathogenic.

Specificity of anti-nuclear antibodies induced in F1 mice undergoing the graft-vs-host reaction: isotypes and cross-reactivities

(C57BL/6 X DBA/2)F1 mice undergoing the graft-vs-host reaction (GVHR) produce autoantibodies after the injection of DBA/2 lymphoid cells. The anti-nuclear antibodies, including anti-poly (ADP-ribose) and anti-extractable nuclear antigens (ENA), in the sera of the autoimmune GVH F1 mice were investigated. Antibodies to double-stranded DNA, single-stranded DNA and ENA were predominantly IgG. In contrast, the autoantibodies to poly(ADP-ribose) were both IgG and IgM, although the former was predominant. These autoantibodies induced by the GVHR showed similar cross-reactivities with a number of nucleic acids to the monoclonal and some serum antinuclear antibodies derived from mice or humans with systemic lupus erythematosus (SLE). These results support the idea that GVH F1 mice are a good model of human SLE.

A study of anti-poly (ADP-ribose) antibodies and an anti-DNA antibody idiotype and other immunological abnormalities in lupus family members

The genetic background of systemic lupus erythematosus (SLE) has been reexamined in a study of the serum of 31 lupus patients and 80 asymptomatic first degree relatives by measuring a common, cross reacting anti-DNA antibody idiotype designated 134, antibodies to poly(ADP-ribose), serum C3, circulating immune complexes, and antinuclear antibodies (ANA). Over 30% of the relatives had raised 134 and anti-poly(ADP-ribose) levels, and 9% had ANA titres greater than 1/20. In contrast, only one relative had a low serum C3 level. These results confirm that immunogenetic abnormalities associated with the production of autoantibodies and particular idiotypes must exist amongst lupus relatives as well as the patients. The production of autoantibodies, however, is not necessarily matched to the clinical expression of SLE.

The production of antibodies to DNA in normal mice following immunization with poly(ADP-ribose)

Monoclonal antibodies were prepared from C57/black mice which had been immunized with poly(ADP-ribose). As expected, some of these antibodies were very specific for poly(ADP-ribose) but, surprisingly, several bound to DNA as well. Analysis of the sera of these mice also showed elevated levels of antibodies to DNA. Monoclonal antibodies against poly(ADP-ribose) were also recovered from unimmunized NZB/W mice which provided an animal model for systemic lupus erythematosus(SLE). These antibodies also cross-reacted with DNA. Comparison of the specificities of the monoclonal antibodies from the two groups of mice showed some striking similarities. In particular, three out of 11 antibodies from the C57/black mice preferred poly(dT) as judged by a solid phase radioimmunoassay. Similarly, 10 out of 17 antibodies from the NZB/W group showed the same type of specificity pattern. These results demonstrate that anti-DNA antibodies can be induced by poly(ADP-ribose) and that some of the autoimmune DNA-binding antibodies found in SLE may result from exposure to poly(ADP-ribose).

Specificity of naturally occurring antibodies to poly(ADP-ribose) in patients with systemic lupus erythematosus: determination by an enzyme linked immunosorbent assay

Serum autoantibodies to poly(ADP-ribose), single-stranded (ss) DNA and double-stranded (ds) DNA in 145 patients with systemic lupus erythematosus (SLE) were measured by an enzyme-linked immunosorbent assay (ELISA). The specificities of the antibodies for poly(ADP-ribose) or for ssDNA in 14 serum samples from different patients, who had relatively high antibody titers to either or both these antigens, were tested by competitive ELISA with poly(ADP-ribose) and ssDNA as inhibitors. The IgG class anti-poly(ADP-ribose) antibodies of 4 serum samples (cases 9, 11, 13 and 14) preferred poly(ADP-ribose) and those of 2 samples (cases 2 and 4) cross-reacted preferentially with ssDNA, while the IgG class anti-ssDNA antibodies of 2 serum samples (cases 9 and 11) significantly cross-reacted with poly(ADP-ribose). Hence, the nature of the antibodies to poly(ADP-ribose) in SLE patients seemed to be different from that of the anti-poly(ADP-ribose) antibodies in autoimmune MRL/Mp-lpr/lpr (MRL/l) mice, which seem to be subpopulations of anti-ssDNA antibodies and react equally well with poly(ADP-ribose) and ssDNA.

MRL/Mp-lpr/lpr mouse derived monoclonal antibodies that recognise determinants shared by poly (ADP-ribose), single stranded DNA and left handed Z-DNA

MRL/Mp-lpr/lpr (MRL/l) mice spontaneously produce antibodies to poly(ADP-ribose) that are cross-reactive with single stranded DNA (ssDNA). Spleen cells from these animals were used for fusion with murine plasmacytoma cells to prepare hybridomas that produce autoantibodies to poly(ADP-ribose). Monoclonal antibodies (MoAb) produced by the selected hybridomas not only preferred ssDNA to poly(ADP-ribose), but also reacted with left handed Z-DNA; the MoAb reflected the nature of serum antibodies to poly (ADP-ribose) in MRL/l mice. These results suggest that similar antigenic determinants exist in poly (ADP-ribose), ssDNA and left handed Z-DNA and that the cross-reactive nature of autoantibodies to poly (ADP-ribose) in MRL/l mice may be the results of expansion of such clones as selected in this experiment.

Naturally occurring antibodies to poly(ADP-ribose) in autoimmune MRL/Mp-lpr/lpr mice

The presence of antibodies to poly(ADP-ribose) was demonstrated in the sera of MRL/Mp-lpr/lpr (MRL/l) mice by an enzyme linked immunosorbent assay (ELISA). Antibody to poly(ADP-ribose) was strongly inhibited by single stranded DNA (ssDNA) and poly(ADP-ribose), and less by double stranded DNA (dsDNA). Affinity purified anti-poly(ADP-ribose) antibodies bound more with immobilized ssDNA than with poly(ADP-ribose), and were significantly inhibited by soluble ssDNA, although poly(ADP-ribose) was the best soluble inhibitor. On the contrary, affinity purified anti-ssDNA antibodies bound best with ssDNA and significantly but less with poly(ADP-ribose); however, they were scarcely inhibited by poly(ADP-ribose). These results suggest that similar antigenic determinants exist in poly(ADP-ribose) and ssDNA. It is conceivable, however, at the present moment that 'naturally occurring antibodies to poly(ADP-ribose)' in MRL/l mice are subpopulations of anti-ssDNA antibodies that react equally well with poly(ADP-ribose) and ssDNA.

Anti-DNA antibody idiotypes in systemic lupus erythematosus

Monoclonal anti-DNA antibodies prepared by the hybridoma technique were used for an analysis of idiotypes of anti-DNA antibodies in systemic lupus erythematosus (SLE). Serum levels of one idiotypic marker, 16/6/R, were higher than normal in 40 of 74 patients (54%) with active SLE, compared with only 6 of 24 patients (25%) with inactive SLE, 9 of 38 patients (25%) with rheumatoid arthritis, and 4 of 96 normal subjects (4%). Levels of the 16/6/R idiotypic marker were determined in serially collected serum samples from 12 patients with SLE. Concordance was found between idiotype levels and clinical activity in 8 of the 12 patients. Levels of the 16/6/R idiotype tended to correlate with levels of antibodies to double-stranded DNA, but in some cases the clinical status was reflected better by the idiotype levels than by the levels of anti-double-stranded-DNA antibodies. Measurement of idiotypes of anti-DNA antibodies may provide information valuable in monitoring the clinical course of patients with SLE.

Measurement of antibody to poly (adenosine diphosphate-ribose): its diagnostic value in systemic lupus erythematosus

Poly (ADP-ribose) and dsDNA binding activity have been measured in sera from 61 patients with systemic lupus erythematosus (SLE) and 188 control sera from 20 normal individuals, 144 patients with clinically similar diseases and 24 patients with drug-induced anti-nuclear antibodies (ANA). Elevated poly (ADP-ribose) binding was not observed with normal sera. Five of 144 samples from diseases entering the differential diagnosis of SLE gave raised poly (ADP-ribose) binding compared with 12 in the 125I-dsDNA binding. Only two of these false positive samples gave elevated binding in the 14C-dsDNA assay. The apparent high specificity of the poly(ADP-ribose) assay was not observed with samples containing drug-induced ANA where 62% had elevated binding values. The frequency with which the poly(ADP-ribose) assay was positive with SLE sera (sensitivity) was lower than either of the dsDNA assays. This low sensitivity and the high rate of false positives in patients with drug-induced ANA limit the value of the poly(ADP-ribose) assay as a diagnostic test for SLE. However the restriction of poly(ADP-ribose) antibody to SLE and patients with drug-induced ANA together with the known role of poly(ADP-ribose) in DNA excision repair suggest that the antibody may be of fundamental significance.