The Clinical Utility of Antihistone Antibodies

Clinical use of anti-histone antibodies in idiopathic and drug-induced lupus

Anti-histone antibodies (AHAs) make their appearance in a number of systemic autoimmune diseases including systemic lupus erythematosus (SLE) and drug-induced lupus erythematosus (DILE). Although being known for over 50 years, they are poorly studied and understood. There is emerging evidence for their use in predicting clinical features of SLE, diversifying their clinical use. AHAs, however, are probably less prevalent in DILE than once thought owing to a move away from older DILE drugs to modern biological agents which do not appear to elicit AHAs. This review examines the historical studies that have defined AHAs and looks at some of the recent work with these autoantibodies.

Toxic epidermal necrolysis-like acute cutaneous lupus erythematosus

The term `Acute Syndrome of Apoptotic Pan-Epidermolysis' (ASAP) designs clinical entities characterized by massive cleavage of the epidermis resulting from hyperacute epidermal basal cell apoptotic injury. It can be seen typically in classic toxic epidermal necrolysis (TEN), but occasionally occurs in non-dru1g-induced entities called `TEN-like' diseases (e.g., lupus erythematosus (LE), acute graft versus host disease and pseudoporphyria).

We would like to highlight the difficulties of establishing differential diagnoses between `TEN-like' LE and drug reactions, especially when LE has not been previously diagnosed. We report a patient with fulminate pattern of epidermal cell injury resulting in a clinical presentation having combined features of drug-induced TEN and acute cutaneous LE with laboratory findings of systemic LE (SLE) and without systemic symptoms or high-risk drug ingestion. Although most cases of ASAP in the setting of LE are drug-induced TEN, there are reported cases of `TEN-like' LE with subacute progression, absence of systemic involvement and lack of drug ingestion. Such cases usually have a previous history of SLE and positive serologic markers. Although some authors observed that these lesions could be related to systemic severity of SLE, this is the first patient reported who progresses to discoid LE and we think it could be a marker of good prognosis. Lupus (2007) 16, 741—745.

The use of laboratory methods in differential diagnosis and treatment of SLE and antiphospholipid syndrome

The detection of autoantibodies has become an important component in the diagnosis and management of systemic lupus erythematosus (SLE) and antiphospholipid syndrome. Their importance lies in the fact that they are not only markers of the disease and used as part of a diagnostic panel, but many of them also show correlation with disease activity. All antibody testing should be interpreted in the context of the clinical features. The antinuclear antibodies test is an effective screening assay in patients with clinical features of SLE. The combination of antinuclear antibodies test, dsDNA and ENA (Ro, La, Sm, RNP) antibodies help to establish the diagnosis of most patients with SLE. New antibodies, such as antinucleosomes and anti-C1q, appear to be useful for SLE diagnosis, monitoring disease activity and predicting renal flares, particularly in dsDNA-negative patients. Anticardiolipin antibodies and lupus anticoagulant are the tests most commonly used in the diagnosis of antiphospholipid syndrome. However, the use of anti-beta(2)-glycoprotein I as a routine diagnostic test remains controversial.

[Drug-induced lupus]

Drug-induced lupus (DIL) is syndrome characterised by the occurrence of lupus-like symptoms and serological findings, following exposure to certain drugs. A substantial number of drugs can induce the positivity of antinuclear antibodies (ANA) but the diagnosis of DIL cannot be done in the absence of clinical features. Most patients with DIL have constitutional symptoms, arthralgia or occasionally arthritis, myalgias, fever and weight loss. These features may take weeks or months to develop and use to be mild with renal and central nervous system happening very rarely. ANA are always positive. They are mainly anti-histone proteins. Antibodies to ds-DNA are a rare finding and would tend to favour a diagnosis of idiopathic SLE. They have been associated with the use of tumour necrosis factor inhibitors (ant-TNF) and minocycline. Some drugs can induce particular symptoms o serological abnormalities and the diagnosis may be more difficult. It is the case of minocycline-induced lupus, which uses to affect young women with anti-ds-DNA and p-ANCA antibodies positive and negative anti-histone antibodies. Treatment with anti-TNF alpha is frequently associated with the development of ANA and anti-DNA. The incidence of ANA positive varies between 23-57% and anti-DNA between 9-33%. However, only a small number of patients will develop DIL or vasculitis. Resolution or marked improvement of the symptoms generally occurs within 2-5 weeks of the drugs withdrawal although some patients may require non-steroid anti-inflammatory drug or low dose steroid. Immunosuppressive drugs may be needed in severe cases with renal or neurological involvement. Some patients remain ANA positive for long periods of time. No treatment is necessary for ANA positive in the absence of clinical features.

Anti-nucleosome and anti-chromatin antibodies are present in active systemic lupus erythematosus but not in the cutaneous form of the disease

The objective of this study is to investigate the presence of anti-nucleosome (anti-NCS) and anti-chromatin (anti-CRT) antibodies in patients with cutaneous lupus erythematosus (CLE) compared with active and inactive systemic lupus erythematosus (SLE). A total of 154 subjects were evaluated: 54 patients presenting CLE, 66 patients with active SLE and 34 with inactive SLE. Lupus activity was assessed using the disease activity index (SLEDAI). Anti-NCS and anti-CRT antibodies were detected by enzyme-linked immunosorbent assay (ELISA). Only one of 54 patients with CLE tested positive for both anti-NCS and anti-CRT antibodies. The prevalence of anti-CRT antibodies was significantly higher in active SLE (84.8%) when compared with inactive SLE (26.4%) and CLE (1.8%) ( P < 0.001). Anti-NCS antibodies were also more prevalent in active SLE patients (74.2%) than inactive SLE (11.7%) and CLE patients (1.8%) ( P < 0.001). The presence of anti-CRT and anti-NCS antibodies was correlated to disease activity in patients with SLE ( r = 0.4937, r = 0.5621, respectively). Furthermore, the detection of both antibodies was correlated with disease activity in patients with SLE who tested negative for anti-dsDNA antibodies ( r = 0.4754 for anti-NCS and r = 0.4281 for anti-CRT). The presence of these two auto-antibodies was strongly associated with renal damage in patients with SLE (OR = 13.1, for anti-CRT antibodies and OR = 25.83, for anti-NCS antibodies). The anti-NCS and anti-CRT antibodies were not found in CLE. In patients with SLE, there is a correlation of these antibodies with disease activity and active nephritis. When compared with anti-dsDNA antibodies, anti-NCS and anti-CRT antibodies were more sensitive in detecting disease activity and kidney damage in lupus patients.

Anti-chromatin (anti-nucleosome) antibodies: diagnostic and clinical value

Anti-chromatin (nucleosome) autoantibodies were one of the first autoantibodies ever detected since they make up the majority of antibodies causing LE Cell formation. The prevalence of anti-chromatin antibodies in systemic lupus erythematosus (SLE) varies from 50% to 100%, being similar to that of the classical positive LE cell. The presence of these antibodies can be used, in conjunction with clinical findings and other laboratory tests, to help in the diagnosis of SLE and drug-induced lupus. Anti-chromatin antibodies have also been found in a lesser percentage of other autoimmune disorders such as primary Sjögren's syndrome and primary antiphospholipid syndrome. The presence of anti-chromatin antibodies has also been linked to glomerulonephritis and disease activity in SLE patients. Recent studies demonstrated the induction of anti-chromatin (anti-nucleosome) antibodies after an anti-tumour necrosis factor (TNF)-alpha agent treatment.

Anti-chromatin (anti-nucleosome) antibodies

Chromatin is the native complex of histones and DNA found in the cell nucleus of eukaryotes. The fundamental subunit of chromatin is the nucleosome, which is composed of a core particle in which 146 bp of helical DNA are wrapped around an octamer made up of two H2A-H2B dimers that surround an H3-H4 tetramer. The prevalence of anti-chromatin (nucleosome) antibodies in systemic lupus erythematosus (SLE) varies from 50% to 90%, being similar to that of the classical positive LE cell. The presence of these antibodies can be used, in conjunction with clinical findings and other laboratory tests, to help in the diagnosis of SLE and drug induced lupus. The presence of anti-chromatin antibodies has also been linked to glomerulonephritis in SLE patients.

Drug bioactivation, covalent binding to target proteins and toxicity relevance

A number of therapeutic drugs with different structures and mechanisms of action have been reported to undergo metabolic activation by Phase I or Phase II drug-metabolizing enzymes. The bioactivation gives rise to reactive metabolites/intermediates, which readily confer covalent binding to various target proteins by nucleophilic substitution and/or Schiff's base mechanism. These drugs include analgesics (e.g., acetaminophen), antibacterial agents (e.g., sulfonamides and macrolide antibiotics), anticancer drugs (e.g., irinotecan), antiepileptic drugs (e.g., carbamazepine), anti-HIV agents (e.g., ritonavir), antipsychotics (e.g., clozapine), cardiovascular drugs (e.g., procainamide and hydralazine), immunosupressants (e.g., cyclosporine A), inhalational anesthetics (e.g., halothane), nonsteroidal anti-inflammatory drugs (NSAIDSs) (e.g., diclofenac), and steroids and their receptor modulators (e.g., estrogens and tamoxifen). Some herbal and dietary constituents are also bioactivated to reactive metabolites capable of binding covalently and inactivating cytochrome P450s (CYPs). A number of important target proteins of drugs have been identified by mass spectrometric techniques and proteomic approaches. The covalent binding and formation of drug-protein adducts are generally considered to be related to drug toxicity, and selective protein covalent binding by drug metabolites may lead to selective organ toxicity. However, the mechanisms involved in the protein adduct-induced toxicity are largely undefined, although it has been suggested that drug-protein adducts may cause toxicity either through impairing physiological functions of the modified proteins or through immune-mediated mechanisms. In addition, mechanism-based inhibition of CYPs may result in toxic drug-drug interactions. The clinical consequences of drug bioactivation and covalent binding to proteins are unpredictable, depending on many factors that are associated with the administered drugs and patients. Further studies using proteomic and genomic approaches with high throughput capacity are needed to identify the protein targets of reactive drug metabolites, and to elucidate the structure-activity relationships of drug's covalent binding to proteins and their clinical outcomes.

Anti-nucleosome, anti-chromatin, anti-dsDNA and anti-histone antibody reactivity in systemic lupus erythematosus

Anti-nucleosome (anti-chromatin) antibodies play a key role in the pathogenesis of systemic lupus erythematosus (SLE). The objective of the present study was to determine the clinical significance of anti-nucleosome (anti-chromatin) antibodies, anti-dsDNA antibodies and anti-histone antibodies in patients with SLE in relation to patients with positive nuclear antibodies and healthy controls. We measured anti-nucleosome (anti-chromatin) antibodies, anti-dsDNA antibodies and anti-histone antibodies in 70 patients with SLE, 35 antinuclear antibody (ANA)-positive subjects without autoimmune disease and 35 blood donors. All antibodies were determined by enzyme-linked immunosorbent assay (ELISA). We obtained the receiver operating caracteristic (ROC) curve and the area under the curve (AUC) for each autoantibody. Likewise, we obtained the sensitivity, specificity and positive and negative likelihood ratios for each autoantibody. The highest AUC was obtained for anti-nucleosome (0.898) and the lowest AUC for a kit for anti-dsDNA (0.725). Stratification of the control group (ANA-positive subjects without autoimmune disease and blood donors) produced significant changes in the AUCs; all AUCs decreased when ANA-positive patients without autoimmune disease were considered as controls and all AUCs increased when blood donors were considered as controls. These effects were less marked in anti-dsDNA antibodies. We observed discrepancies between kits (anti-nucleosome and anti-chromatin and two for anti-dsDNA). The highest sensitivity for SLE was obtained for anti-nucleosome antibodies (86%) and the highest specificity was obtained for anti-dsDNA antibodies (90%). In conclusion, anti-nucleosome and anti-chromatin kits show different degrees of clinical accuracy due to the cut-off selected by the manufacturer. Once the kits with the best performance and the optimal cut-offs have been selected, anti-nucleosome antibodies and anti-dsDNA antibodies provide similar information in established SLE.

Anti-chromatin (anti-nucleosome) autoantibodies

Anti-chromatin autoantibodies were one of the first autoantibodies ever detected since they make up the majority of antibodies causing LE Cell formation. Anti-chromatin autoantibodies have had many names over the last few decades: LE cell factor; anti-nucleosome; anti-deoxyribonucleoprotein (DNP); and anti-(H2A-H2B-DNA). These autoantibodies are found in approximately 75% of people with systemic lupus erythematosus and up to 100% of people with drug-induced lupus. They are also found in 20-50% of patients with autoimmune hepatitis type I (lupoid hepatitis). Anti-chromatin are not generally found in any other disease, thus showing very good sensitivity and specificity for patients with lupus, drug-induced lupus and lupoid hepatitis. A number of studies have shown that in patients with lupus, anti-chromatin often correlates better with kidney disease than anti-DNA. Recent genetic analyses of murine models of lupus have identified at least three loci that work together to cause anti-chromatin antibodies and glomerulonephritis in mice. It will be an important breakthrough when the functions of the genes at these loci are identified.

Antinuclear antibody testing

The ANA test is an excellent screening test for patients with SLE and a few other connective tissue diseases. The LE cell preparation is an assay that is subjective and costly. Because of the presence of a superior screening test (the ANA) and superior specific auto-antibody tests, the author recommends that the use of LE cell preparations be discontinued. ANA screening tests may be performed either by indirect microscopic serology (usually IFA) or EIA. The latter technique is readily automated and many new products for this screening test have appeared in the past decade. The products differ, however, and laboratories are cautioned to test each in the context of the clinical needs of their clinicians. Proper use of the ANA test requires each laboratory to determine the cutoff used under their conditions of assay. Although either ANA screening test has a high negative predictive value in numerous studies, proper selection of patients to be tested is key to improving the predictive value of a positive result. The American College of Rheumatism criteria are reviewed and recommended as part of the patient selection process for this testing.

Autoantibodies Associated with Rheumatic Diseases

The identification of circulating autoantibodies contributes to the correct diagnosis as well as to the follow-up of rheumatic diseases. Some autoantibodies are even included in diagnostic and classification criteria for these types of autoimmune diseases. There are several relatively specific screening and identification methods for the measurement of autoantibodies available. The type of assay crucially influences the diagnostic value of the parameters. In general, routine laboratories should prefer enzyme immunoassays (ELISA) using well characterized antigens, although ELISA tests tend to produce more false-positive and true weakly positive results, which reduce their positive predictive value. Therefore one should be aware that laboratory results can only be properly interpreted when there is a correlation with the clinical situation and when the limitations of the technologies used for autoantibody identification have been taken into consideration. A diagnostic algorithm consisting of screening and identification steps should be established by each laboratory in order to create a rational, evidence-based and cost-effective basis for the diagnosis of rheumatic diseases.

Drug-induced rheumatic disorders: incidence, prevention and management

The purpose of this article is to review the causes, the clinical manifestations and the management of the more frequent drug-induced rheumatic disorders. These include: (i) articular and periarticular manifestations induced by fluoroquinolones, nonsteroidal anti-inflammatory drugs, injections of corticosteroids, and retinoids; (ii) multisystemic manifestations such as drug-induced lupus and arthritis induced by vaccination, Bacillus Calmette-Guerin therapy and cytokines; (iii) drug-induced disorders of bone metabolism (corticosteroid-induced osteoporosis, drug-induced osteomalacia and osteonecrosis); and (iv) iatrogenic complex regional pain syndromes. Disorders caused by nonpharmacological and rarely used treatments have been deliberately excluded. Knowledge of these drug-induced clinical symptoms or syndromes allows an earlier diagnosis and treatment, and earlier drug withdrawal if necessary. With the introduction of new medications such as the recombinant cytokines and antiretroviral treatments, the number of drug-induced rheumatic disorders is likely to increase.