Autoantigenic histone epitopes: a comparison between procainamide- and hydralazine-induced lupus

Canine Systemic Lupus Erythematosus. II: Antinuclear Antibodies

The frequency and the specificities of antinuclear antibodies (ANAb) were studied in dogs with systemic lupus erythematosus (SLE) and compared to those found in normal dogs and in dogs with various infectious diseases. Whole ANAb were detected by immunofluorescence. Anti-double-stranded DNA Ab were found in only 2% of SLE dogs, whereas anti-single-stranded DNA Ab were present in 21.4% of SLE dogs and in 26.8% of dogs with infectious disease. Antihistone Ab were frequently observed in SLE dogs (71%) and are essentially directed against trypsin-resistant epitopes of H3, H4 and H2A. The Western blots of nuclear extracts of HeLa cells were recognized mainly by type 1 Ab (30%, reacting with bands of 43, 36, 35, 34, 30 and 27 kDa) and by anti-Sm Ab (12%) associated with anti-RNP Ab. Anti-SSA and anti-SSB Ab were rare.

[Specificities and clinical significance of autoantibodies directed against histones]

Systemic lupus erythematosus (SLE) is an autoimmune disease characterized by the occurrence of numerous autoantibodies directed against nuclear antigens. Anti-histone antibodies (AHA) are as prevalent as their anti-dsDNA counterparts in SLE. Despite their frequency and potential importance, there have not been given much attention to AHA until recently. Nucleosomes, the fundamental repeating units of the chromatin, are formed of complexes of histones and DNA. The nucleosome core particle is composed of a central tetramer of 2 molecules each of H3 and H4 flanked by 2 dimers of H2A and H2B and surrounded by 2 superhelical turns of approximately 146 base pairs of DNA. The full nucleosome contains a molecule of H1 located at the point where DNA enters and exits the nucleosome. Recent studies have shown that the post transcriptional modification of histone changes chromatin structure to regulate transcription and the concept of this mechanism "epigenetics" has become center of attention in the field of basic cell biology. There have been described diverging specificities of AHA. Many attempts to locate antigenic determinants recognized by AHA have been made and H1 and H2B have been thought as common targets in lupus patients. Studies on murine models of lupus have shown several interesting findings. The universal epitope is located on H2B in (NZBxNZW)F1 mice. In addition to core histones, MRL-MP/Fas(lpr) mice develop high titers of autoantibodies to H1. Autoimmunity to chromatin regularly involves humoral immune responses directed against H1. These histones appear to be an early (possibly initial trigger) autoantigen for this autoimmune response in lupus.

Antinuclear antibody testing in systemic autoimmune disease

This article discusses the use and interpretation of antinuclear antibody (ANA) testing in connective tissue diseases. Methods of ANA detection are discussed and analyzed in detail as is the role of ANAs in systemic lupus, scleroderma, and polymyositis, connective tissue diseases with prominent pulmonary involvement.

Nuclear antigen histone H1 is primarily involved in lupus erythematosus cell formation

OBJECTIVE

To elucidate the nature of the antigen reactive with the "lupus erythematosus (LE) cell factor," the autoantibody involved in the LE cell phenomenon.

METHODS

Serum samples from systemic lupus erythematosus (SLE) patients who were positive for the LE cell phenomenon (LEc+) and SLE patients who were negative for the LE cell phenomenon (LEc-) were used to characterize the nuclear antigen bound by the LE cell factor, by immunoblotting and immunoprecipitation techniques.

RESULTS

All LEc+ sera, but none of the LEc- sera, uniformly reacted with a double band of MW approximately 30 kd in nuclear extracts. Depletion of nuclear protein extracts of antigens bound by pooled LEc- serum allowed precipitation of a low molecular weight protein by pooled LEc+ serum. This protein was able to block LE cell formation by LEc+ serum. Based on its reactivity with antihistone antibody and an electrophoretic mobility identical with that of precipitated and purified histone H1, this protein was identified as histone H1. Moreover, all LEc+ sera, but none of the LEc- sera, reacted with purified histone H1 by immunoblotting, whereas other histones were reactive with both types of sera. In addition, purified histone H1, but none of the other histones, strongly inhibited the induction of LE cells by LEc+ serum.

CONCLUSION

Histone H1 represents the major antigenic component recognized by the LE cell factor. Thus, the LE cell phenomenon appears to be due primarily to anti-histone H1 reactivity.

Molecular biology of autoantigens in rheumatic diseases

The advent of molecular biologic techniques has provided new approaches that are of great utility to the study of autoimmune-mediated responses. In the past few years, there has been a remarkable accumulation of knowledge concerning the molecular identity and function of autoantigens, and further consolidation for the use of autoantibodies as diagnostic markers in clinical rheumatology. The understanding of basis methodologies in molecular biology applied to the study of autoantigens, in particular, techniques for cloning and analyzing genes that are important in rheumatic diseases, is valuable for both basic scientists and clinicians interested in diagnostic and prognostic markers of various connective tissue diseases.

Clinical relevance of autoantibodies in systemic rheumatic diseases

Autoantibodies directed to intracellular antigens are serological hallmarks of systemic rheumatic diseases. Identification of circulating autoantibodies is helpful in establishing the correct diagnosis, indicating the prognosis and providing a guide to treatment and follow-up. Some autoantibodies are included in diagnostic and classification criteria for diseases such as anti-Sm antigen and anti-double-stranded DNA antibodies in systemic lupus erythematosus, anti-U1 nuclear ribonucleoprotein antibodies in mixed connective tissue disease, and anti-SS-A/Ro and anti-SS-B/La antibodies in Sjögren's syndrome. Over the past 30 years, the identification of new autoantibody systems was advanced by the initiation or adaptation of novel techniques such as double immunodiffusion to detect antibodies to saline-soluble nuclear antigens, extraction-reconstitution and ELISA techniques to detect histone and chromatin antibodies, immunoblotting and immunoprecipitation to detect a wide range of antibodies directed against naturally occurring and recombinant proteins. These techniques have been made possible by advances in cellular and molecular biology and in turn, the sera from index patients have been important reagents to identify novel intracellular macromolecules. This paper will focus on the clinical relevance of several autoantibody systems described by Tan and his colleagues over the past 30 years.

Sequence analysis and fine specificity of two human monoclonal antibodies to histone H1

Two human IgM lambda monoclonal antibodies (MAb) derived from the splenic lymphocytes of patients with idiopathic thrombocytopenia (Ben) and systemic lupus erythematosus (Wri) were studied. BEN-27 and WRI-170 hybridoma supernatants were screened for binding to ssDNA, dsDNA, poly (ADP-ribose), cardiolipin, histone subclasses and Klebsiella K30 cell wall antigen. Of this panel of antigens, BEN-27 and WRI-170 antibodies reacted only with histone H1. Their fine specificity was defined by direct and inhibition ELISA with synthetic peptides of the major human H1b variant. Antibody WRI-170 was shown to bind to both the N- and C-terminal peptides encompassing residues 1-16 and 204-218 of H1b whereas BEN-27 reacted only with peptide 204-218. To analyse the genetic origin of these autoantibodies, we determined the nucleotide sequence of the heavy (H) and light (L) chain variable regions of these two hybridomas. BEN-27 and WRI-170 MAbs were found to use VH1-DN1-JH4/V lambda 3-J lambda 2 and VH3-DIR2-D21/9-JH1/V lambda 2-J lambda 2 gene segment combinations respectively. Between 70 and 95% homology was demonstrated when the mRNA sequences for BEN-27 and WRI-170 were compared with published VH and V lambda germline sequences. This finding suggests that BEN-27 heavy and light chains and WRI-170 light chain use unidentified VH and V lambda germline gene segments whereas WRI-170 heavy chain derives from a VH gene segment recently identified. It is noteworthy that the CDRs of the two MAbs contain several negatively charged amino acids which are assumed to be of critical importance in antigen binding. Moreover, striking similarities are observed between BEN-27 heavy chain CDR2 and a previously described murine anti-H1 Ab heavy chain CDR2.

Epitope mapping of histone 5 (H5) with systemic lupus erythematosus, procainamide-induced lupus and hydralazine-induced lupus sera

To define the linear epitopes on H5 that react with systemic lupus erythematosus (SLE) and drug-induced lupus (DIL) sera, concurrent overlapping hexameric peptides corresponding to the sequence of H5 were synthesized by stepwise elongation of the polypeptide chains on polyethylene supports. The hexapeptides were tested for reactivity with 8 SLE and 8 DIL sera using an enzyme linked immunosorbent assay (ELISA). SLE and hydralazine-induced lupus (HIL) antibodies were most reactive with peptide 45 (SSRQSI) and patients with procainamide-induced lupus (PIL) were most reactive with peptide 24 (SHPTYS). The epitopes of highest reactivity were in the globular domain of H5. Low reactivity was observed with carboxyl terminal peptides. These findings differ from immunoblotting studies of protease cleaved peptides which have previously shown that the H5 determinants are in the carboxyl terminus.

Autoantibodies associated with lupus induced by diverse drugs target a similar epitope in the (H2A-H2B)-DNA complex

IgG reactivity with the (H2A-H2B)-DNA complex, a subunit of the nucleosome, has been detected in many patients with lupus induced by procainamide and quinidine, but the similarity among the epitopes targeted by these antibodies in this heterogeneous patient group as well as the prevalence of this specificity in lupus induced by other drugs is unknown. Studies with histone-DNA complexes formed by sequential addition on a solid phase demonstrated that complexes containing single histones had negligible antigenicity, indicating that DNA stabilizes a protein epitope in the H2A-H2B dimer or that the complete epitope is generated by a surface feature involving H2A-H2B and DNA. F(ab')2 isolated from a patient with procainamide-induced lupus blocked greater than 90% of the anti-[(H2A-H2B)-DNA] reactivity in six of six sera from patients with lupus induced by procainamide, four of four quinidine-induced patients and in sera from patients with lupus induced by acebutolol, penicillamine, and isoniazid, but not methyldopa or auto-antibodies to the component macromolecules. Fab fragments purified from the IgG of two quinidine-induced lupus patients and patients with isoniazid- and procainamide-induced lupus retained 39% +/- 8% of their original IgG reactivity compared to 34 +/- 28% of the original anti-tetanus toxoid activity of Fab fragments in two of the same sera and two normal sera. These results indicate that anti-[(H2A-H2B)-DNA] does not require divalent antigen-antibody complexes for stability, and that the complete epitope is created by the monomeric, trimolecular histone-DNA complex. We conclude that despite their pharmacologic and chemical heterogeneity, many lupus-inducing drugs elicit near identical autoantibodies.

Autoantibody specificity in drug-induced lupus and neutrophil-mediated metabolism of lupus-inducing drugs

A long-term side effect of therapy with a variety of drugs is a syndrome resembling the idiopathic autoimmune disease, systemic lupus erythematosus. Essentially all patients with drug-induced lupus display autoantibodies to nuclear histone components whose specificity appears to be related to the higher order structure of histones existing in chromatin. IgG antibodies to H1 and the (H2A-H2B)-DNA complex were observed in most patients with lupus induced by procainamide, hydralazine, and quinidine, whereas the H3-H4 tetramer, comprising half the mass of the nucleosome core particle, was largely nonantigenic. IgM antibodies to (H2A-H2B)-containing chromatin subunits were common also. IgM reactivity was observed with the DNA-free H3-H4 tetramer and with H1, especially in hydralazine-induced lupus. These results suggest that IgM antihistone antibodies may result from autoimmunization with a nonnative form of chromatin, whereas IgG antibodies may be selected for reactivity with H1 and a native form of the (H2A-H2B)-DNA subunit of the nucleosome. The chemical basis for induction of autoimmunity by drugs is unclear because lupus-inducing drugs do not have a common structural feature or biological activity nor are they capable of specific reactions with histones, the principal target antigen. However, in the presence of activated neutrophils, procainamide is transformed metabolically to the cytotoxic procainamide-hydroxylamine. Mixing experiments and cell-free studies demonstrated that procainamide was cooxidized with H2O2 by myeloperoxidase released when neutrophils undergo the respiratory burst and degranulation reactions. Preliminary results indicate other lupus-inducing drugs are also biotransformed by this mechanism suggesting that a common denominator linking these drugs may be the capacity to be oxidized to reactive metabolites by the action of activated phagocytic cells.

The role of leukocyte-generated reactive metabolites in the pathogenesis of idiosyncratic drug reactions

Evidence strongly suggests that many adverse drug reactions, including idiosyncratic drug reactions, involve reactive metabolites. Furthermore, certain functional groups, which are readily oxidized to reactive metabolites, are associated with a high incidence of adverse reactions. Most drugs can probably form reactive metabolites, but a simple comparison of covalent binding in vitro is unlikely to provide an accurate indication of the relative risk of a drug causing an idiosyncratic reaction because it does not provide an indication of how efficiently the metabolite is detoxified in vivo. In addition, the incidence and nature of adverse reactions associated with a given drug is probably determined in large measure by the location of reactive metabolite formation, as well as the chemical reactivity of the reactive metabolite. Such factors will determine which macromolecules the metabolites will bind to, and it is known that covalent binding to some proteins, such as those in the leukocyte membrane, is much more likely to lead to an immune-mediated reaction or other type of toxicity. Some reactive metabolites, such as acyl glucuronides, circulate freely and could lead to adverse reactions in almost any organ; however, most reactive metabolites have a short biological half-life, and although small amounts may escape the organ where they are formed, these metabolites are unlikely to reach sufficient concentrations to cause toxicity in other organs. Many idiosyncratic drug reactions involve leukocytes, especially agranulocytosis and drug-induced lupus. We and others have demonstrated that drugs can be metabolized by activated neutrophils and monocytes to reactive metabolites. The major reaction appears to be reaction with leukocyte-generated hypochlorous acid. Hypochlorous acid is quite reactive, and therefore it is likely that many other drugs will be found that are metabolized by activated leukocytes. Some neutrophil precursors contain myeloperoxidase and the NADPH oxidase system, and it is likely that these cells can also oxidize drugs. Therefore, although there is no direct evidence, it is reasonable to speculate that reactive metabolites generated by activated leukocytes, or neutrophil precursors in the bone marrow, could be responsible for drug-induced agranulocytosis and aplastic anemia. This could involve direct toxicity or an immune-mediated reaction. These mechanisms are not mutually exclusive, and it may be that both mechanisms contribute to the toxicity, even in the same patient. In the case of drug-induced lupus, a prevalent hypothesis for lupus involves modification of class II MHC antigens.(ABSTRACT TRUNCATED AT 400 WORDS)

Antibodies to histones in systemic lupus erythematosus: prevalence, specificity, and relationship to clinical and laboratory features

Antibodies to histones (AHA) are commonly found in patients with systemic lupus erythematosus (SLE). However, the full profile of AHA and their clinical associations remains unclear. A total of 111 patients with SLE were studied, including 13 patients in whom multiple serum samples were available over several years. IgM, IgG, and IgA antibodies to total core histones, histone complexes, and individual histones were determined by highly sensitive enzyme linked immunosorbent assays (ELISAs). Antibodies to histones were detected in 74% of serum samples, though only at low levels in half of these. Antibodies to each of the individual histones (H1, H2A, H2B, H3, H4) occurred with similar frequencies except for IgG and IgA antibodies to H4, which were uncommon. In contrast, antibodies to the histone complexes H2A-H2B and H3-H4 were detected in only two serum samples and thus do not appear to be a feature of SLE. All three major isotypes of AHA were common and usually occurred with similar frequencies to one another for the various histone specificities. There were few clinical or laboratory associations with AHA; the strongest was between IgG antibodies to total core histones and antibodies to native DNA. Similarly, there was no association between the presence of AHA and disease activity. However, for the patients as a group and in one patient alone, periods of SLE disease activity were associated with higher levels of AHA. Although the profile of antibodies to individual histones varied with time, no profile was identified that corresponded with any specific disease manifestations. It is concluded from this study that although AHA are common in patients with SLE, their clinical value in this syndrome must, at present, be considered limited.

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.

Drug-induced anti-histone autoantibodies display two patterns of reactivity with substructures of chromatin

Increasing evidence suggests that autoantibodies in the rheumatic diseases are a consequence of immune selection by self-material, but the nature of the in vivo immunogen is unknown. Insight into this problem may be obtained by measuring autoantibody binding to various forms of a target antigen. Antihistone antibodies arising as a side effect of therapy with various drugs offer an opportunity to explore this premise because many forms of histone have been characterized and adapted to ELISA formats. Two patterns of antibody reactivity were observed. All 21 patients with symptomatic procainamide-induced lupus and 7 of 12 patients with quinidine-induced lupus had IgG antibodies reacting predominantly with the (H2A-H2B)-DNA complex and with chromatin. In contrast, antibodies in 19 of 24 patients taking procainamide without accompanying lupus-like symptoms did not show any pattern. The second pattern was observed in 18/19 chlorpromazine-treated patients and 14/17 patients with hydralazine-induced lupus in which IgM antibodies displayed more reactivity with DNA-free histones than with the corresponding histone-DNA complexes and almost no binding to H1-stripped chromatin. Absorption studies were entirely consistent with these results. Thus, the two patterns of reactivity with nucleosomal components reflect the molecular substructure of chromatin, suggesting that two processes underlie antihistone antibody induction by drugs. In one, IgG autoantibodies appear to be elicited by chromatin, whereas in the other, autoimmune tolerance to native chromatin appears largely intact, and IgM antibodies may be driven by DNA-free histone.

Subnucleosome structures as substrates in enzyme-linked immunosorbent assays

Histone preparations preserving the tertiary and quaternary structure of histone-histone complexes and histone-DNA complexes, as well as individual histones, were isolated or reconstituted. Various parameters were tested in order to determine the suitability of these complexes for use as substrates in enzyme-linked immunosorbent assays. The protein concentration required to saturate the solid phase was determined, and the amount of bound protein was quantified by the micro-bicinchoninic acid protein assay. In addition, the relative DNA content of solid phase antigen was measured by the binding of monoclonal anti-native DNA antibodies. Prototype sera representing different disease groups produced reproducible and unique patterns of reactivity on the panel of antigens, demonstrating the lack of substantial assay bias. Two substrates, the H2A-H2B dimer and the H2A-H2B-DNA complex, both appear to be oriented in a random manner on the solid phase, leaving a number of different epitopes exposed to the solution. This novel set of histone antigens can now be used to define the specificity of anti-histone antibodies in relation to the quaternary structure of chromatin.

Antibodies from patients with systemic lupus erythematosus and drug-induced lupus bind determinants on histone 5 (H5)

The antigenic domains of histone 5 (H5), a highly conserved variant of histone 1 (H1), were studied in relation to their reactivity with autoantibodies found in the sera of patients with systemic lupus erythematosus (SLE) and drug-induced lupus (DIL). While some H5 antibodies cross-react with H1, adsorption and immunoblotting studies have identified H5-specific antibodies as well. After proteolytic cleavage of H5 peptides, the reactivity of sera from these patients was tested by Western immunoblotting. All SLE (9/9) and DIL (7/7) sera bound an antigenic determinant in the carboxyl (C) terminus of H5 while none of the sera bound to the amino (N) terminus or the central hydrophobic domain. Although the reactivity of DIL sera with the purified H5 peptides was weaker than that of SLE sera, the antigenic domains bound by both groups of sera were the same. These observations demonstrate that the H5 domains reacting with DIL sera are restricted to the carboxyl terminus and are therefore no less restricted than those reacting with SLE sera. Further, the potential epitopes in the carboxyl terminus of H5 do not have a high degree of sequence identity with known mammalian peptides.

CD4+ cells treated with DNA methylation inhibitors induce autologous B cell differentiation

The DNA methylation inhibitor 5-azacytidine induces autoreactivity in cloned CD4+ T cells, but the functional consequences of this response are unknown. We now report that CD4+ T cells treated with 5-azacytidine respond to autologous antigen-presenting cells and induce autologous B cell differentiation without exogenous antigen or mitogen. This mechanism could play a role in some autoimmune diseases characterized by T cell DNA hypomethylation and polyclonal B cell activation.

Lupus-inducing drugs alter the structure of supercoiled circular DNA domains

We analyzed the effects of procainamide (PROC), hydralazine (HYD), N-acetylprocainamide (NAPA), and L-canavanine (CAN) on circular supercoiled plasmids as models for chromosomal loop domains. The supercoil-dependent B-Z equilibrium in recombinant plasmids was used as an indicator of structural changes induced in circular DNA. Two-dimensional gel electrophoresis showed that PROC and HYD strongly inhibited supercoil-induced Z-DNA formation, whereas NAPA caused less pronounced changes in the B-Z equilibrium, and CAN had no effect. Gel retardation assays showed that the binding of a Z-DNA-specific autoimmune antibody to a Z-DNA-containing plasmid was strongly perturbed by HYD, but not influenced by CAN. Both PROC and NAPA showed moderate inhibition of antibody binding. Our results demonstrate the different potentials of these 4 drugs to interact with DNA and to alter the tertiary topology of DNA domains. It is conceivable that the in vivo capacity of PROC and HYD to induce antinuclear antibodies may be related to their ability to influence structural features in chromosomal DNA domains or nucleosomes, thus liberating antigenic structural epitopes in DNA and/or DNA-associated proteins.

Drug-induced rheumatic syndromes. Diagnosis, clinical features and management

In order to avoid inappropriate therapy and prolonged morbidity, it is important to recognise when a patient's rheumatic complaints are due to drugs. However, this is often difficult because of the large number of drugs that have been implicated and the diversity of clinical presentations. Arthropathy may be seen with several different syndromes, including drug-induced lupus erythematosus (DILE), serum sickness and gout. The most widely reported of these is DILE, which usually develops after some months or even years of drug therapy. While many authors do not specifically require their presence for the diagnosis of DILE, antinuclear antibodies have been detected in the great majority of reported patients with DILE, whatever the causative drug. In contrast, patients who develop arthropathy soon after commencing a drug rarely have antinuclear antibodies and appear to be distinct from patients with DILE. Apart from arthropathy, a number of other syndromes that appear to have an immunological basis may be induced by drugs. Cutaneous vasculitis is not uncommon and drugs are frequently considered to be the aetiological factor. Whether drugs may cause larger vessel systemic vasculitis is less certain. Rarely, polymyositis and scleroderma-like syndromes have been associated with drug therapy. Corticosteroid-induced osteoporosis is a complication of all the corticosteroid preparations that are widely used at present. However, the development of deflazacort, a so-called 'bone-sparing' steroid, has raised the possibility that the effect of corticosteroids on bone may be separable, at least in part, from the other actions of these drugs. Data have been conflicting with regard to whether there is a 'safe' dose of corticosteroid. Similarly, it is unclear whether prophylactic therapy with agents such as calcium, fluoride and vitamin D is beneficial. Nonetheless, recent findings suggest that approaches will be developed to minimise the risk of osteoporosis in patients who require corticosteroids. There are a number of other ways in which drugs may affect bones. Osteomalacia is a well-known but uncommon complication of treatment with anticonvulsants and occasionally other drugs. The mechanism probably relates to the induction of hepatic enzymes and the consequent increased metabolism of vitamin D in patients with borderline levels initially. Osteosclerosis may also result from drug therapy; usually with fluoride or retinol (vitamin A) and its analogues. With continued research, the true spectrum of drug-induced rheumatic syndromes should become more clearly defined.(ABSTRACT TRUNCATED AT 400 WORDS)

Methyldopa-induced systemic lupus erythematosus

Thirteen months after starting methyldopa therapy, a 55-year-old white male patient presented with a syndrome of hemolytic anemia, arthritis, photosensitivity, and a positive antinuclear antibody test result. Methyldopa-induced antinuclear antibodies were mainly IgG, directed against class H1 histones. Antibodies to native DNA and nonhistone proteins were not detected. Upon withdrawal of methyldopa therapy, and with a short course of prednisone and danazol therapy, the patient's symptoms and hemolytic anemia resolved. His clinical symptoms and serologic abnormalities returned to normal and remained negative after 2 years of followup.

Association of antibody to histone complex H2A-H2B with symptomatic procainamide-induced lupus

Antinuclear antibodies develop in most patients who are given prolonged procainamide therapy, but clinical symptoms resembling those of lupus appear in only 15 to 20 percent of such persons. No objective marker for symptomatic procainamide-induced lupus has been described. However, IgG antibodies to the histone complex H2A-H2B have previously been reported in this disorder, and it has been suggested that antiguanosine antibodies may be a marker for major manifestations of procainamide-induced lupus. We therefore tested for these antibodies in 20 symptomatic and 31 asymptomatic patients treated with procainamide. Most of the symptomatic patients had multiple manifestations of drug-induced lupus; resolution of symptoms after the discontinuation of procainamide was required for inclusion in the symptomatic group. All 20 symptomatic patients had elevated IgG antibodies to H2A-H2B, in contrast to only 2 asymptomatic patients (P less than 0.001). This activity was absent in patients not treated with procainamide and in patients with lupus induced by hydralazine or quinidine. IgG antiguanosine was elevated as compared with normal controls in 13 of 20 symptomatic and 19 of 31 asymptomatic patients--a finding that did not distinguish between symptomatic and asymptomatic patients. We conclude that IgG antibodies to H2A-H2B are a sensitive and specific marker for procainamide-induced lupus. The striking correlation between antibodies to H2A-H2B and symptomatic disease suggests a possible association between this antibody and the underlying pathogenic events.

In vitro anti-histone antibody production by peripheral blood cells from patients with systemic lupus erythematosus

Anti-histone antibodies (AHA) have been demonstrated frequently in the sera of patients with systemic lupus erythematosus (SLE). In the present studies, we found that peripheral blood mononuclear leukocytes (PBL) from a large subset of SLE patients spontaneously produce elevated levels of AHA in culture. In contrast, detectable production by normal mononuclear cells was extremely rare. Spontaneous production by patients' PBL correlated with both disease activity and elevated serum AHA levels, and thus appeared to reflect in vivo production. Interestingly, spontaneous AHA production was independent of polyclonal B-cell activation as measured by total Ig synthesis in culture. Production also appeared to be T-cell-independent in that cultures depleted of T cells produced AHA levels similar to those of cultures with unseparated PBL. Although PBL from normal individuals rarely produce AHA spontaneously, the presence of histone-specific B cells in normal peripheral blood could be detected after pokeweed mitogen stimulation. The present studies provide a basis for a further understanding of the mechanisms responsible for autoantibody production in SLE.