Histone antibodies in systemic lupus erythematosus. A possible diagnostic tool

Significance of co-positivity for anti-dsDNA, -nucleosome, and -histone antibodies in patients with lupus nephritis

OBJECTIVE

The aim of this study was to define the clinical, histopathologic, and prognostic features associated with simultaneous positivity for anti-dsDNA, -nucleosome, and -histone antibodies (3-pos) in Korean patients with biopsy-proven lupus nephritis (LN).

METHODS

The 102 patients included in the study had undergone kidney biopsy prior to the start of induction treatment, were treated with immunosuppressives, and followed-up for >12 months.

RESULTS

In total, 44 (43.1%) of the 102 LN patients were 3-pos. Patients with 3-pos had a higher SLEDAI-2K score (p = .002), lower lymphocyte count (p = .004), and higher rates of proteinuria > 3.5 g/24 h (p = .039) and positivity for urinary sediments (p = .005) at the time of renal biopsy than non-3-pos patients. 3-pos patients had a more proliferative form of LN (p = .045) in the renal histopathologic findings, and as co-positivity gradually increased from 0 to 3, the total activity score in the renal biopsy findings increased significantly (p = .033). In addition, 3-pos patients had a more rapid eGFR decline than non-3-pos patients after a follow-up of 83.2 months (p = .016).

CONCLUSIONS

Our findings suggest that 3-pos is related to severe LN and that 3-pos patients are more likely to experience a rapid decline of renal function than non-3-pos patients.KEY MESSAGEPatients with co-positivity for anti-dsDNA, -nucleosome, and -histone antibodies (3-pos) had higher disease activity and a worse renal histopathology than those without co-positivity.3-pos patients had a more rapid decline of renal function than non-3-pos patients.

Antibodies to histone in the pediatric population: a retrospective chart review

BACKGROUND

Antibodies to histone have been associated in the adult literature with systemic lupus erythematosus(SLE) and drug induced lupus(DILE). Little data is available regarding the spectrum of pathology that antibodies to histone encompass in the pediatric population. Prior studies suggest an association with SLE, juvenile idiopathic arthritis(JIA), uveitis and linear scleroderma.

METHODS

Patient charts were reviewed that contained positive anti-histone antibody testing during a consecutive three year period. Patient diagnosis along with the presence of: anti-histone antibody titer, ANA, and the presence of other autoantibodies to SSA, SSB, Sm, RNP, dsDNA and chromatin were obtained. The frequency of SLE, JIA and DILE was further investigated in specific subsets.

RESULTS

139 individual charts were reviewed containing 41 different diagnoses. The most common diagnosis was hypermobility arthralgia with 22 patients. The most frequent rheumatologic diagnosis was JIA(nonsystemic) with 19. 13 patients in this study were diagnosed with SLE and 2 with DILE. 18 patients had other autoantibody production, of these, 11 had SLE or DILE. Only one of 62 patients with a weak antihistone antibody titer(1.0-1.5) was diagnosed with SLE. When strong titers are present(> 2.5), the antihistone antibody test was associated with a greater than 50% incidence of an underlying rheumatologic disease and ten times higher incidence of SLE than a weak titer. In regards to the frequency of SLE, there was a statistically significant difference between weak and moderate titers and between weak and strong titers.

CONCLUSION

The presence of anti-histone antibody was observed in a variety of diagnoses in the pediatric population. Overall, the presence of anti-histone antibodies appears to have poor diagnostic utility for any specific condition. However, diagnostic utility for SLE does appear to improve with higher titers, when combined with other autoantibody positivity. Strength of titer did not appear to be a factor for JIA, but was the most frequently observed rheumatologic disease in this study.

Comparison of two anti-histones antibodies commercial assays in an immunology laboratory and systemic lupus erythematosus

BACKGROUND

Anti-histones antibodies (AHAs) are antibodies directed against histone proteins - structural proteins that provides scaffolding for DNA to be wrapped around. AHAs, measured in the serum, are diagnostically helpful in cases of systemic lupus erythematosus (SLE) and drug-induced lupus erythematosus (DILE). In the diagnostic laboratory, they may be measured by enzyme-linked immune-sorbent assay (ELISA) or line immunoassays (LIA); however, the performance of these have never been directly compared in the literature.

METHODS

We evaluated a commonly used commercial ELISA and LIA to compare the performance in our immunology laboratory. Retrospective and prospective analyses were undertaken over a 5.5-year period. We also examined their performance in the model disease of SLE and compared their performance to disease activity and the main clinical features.

RESULTS

One hundred and thirty-five patients were evaluated including 65 SLE patients. Based on the quantitative cut-offs, there was only moderate agreement between the two assays (κ = 0.444). Both assays only had modest agreement with the clinical situation of the evaluated patients. When considered within the SLE context, both assays were moderately correlated with disease activity. Positive AHAs by ELISA were associated with SLE cytopaenias, and both ELISA and LIA correlated with positive anti-double stranded DNA.

CONCLUSIONS

Moderate agreement analytically were seen between ELISA and LIA methods in a general laboratory cohort. Both assays were comparable in their diagnostic performance. ELISA detection of AHAs appears to have some clinical use in our cohort of SLE patients. Future studies are required to explore the clinical utility of AHAs in SLE and other disorders.

Autoantibodies in Neuropsychiatric Systemic Lupus Erythematosus (NPSLE): Can They Be Used as Biomarkers for the Differential Diagnosis of This Disease?

Systemic lupus erythematosus is a complex immunological disease where both environmental factors and genetic predisposition lead to the dysregulation of important immune mechanisms. Eventually, the combination of these factors leads to the production of self-reactive antibodies that can target any organ or tissue of the human body. Autoantibodies can form immune complexes responsible for both the organ damage and the most severe complications. Involvement of the central nervous system defines a subcategory of the disease, generally known with the denomination of neuropsychiatric systemic lupus erythematosus. Neuropsychiatric symptoms can range from relatively mild manifestations, such as headache, to more severe complications, such as psychosis. The evaluation of the presence of the autoantibodies in the serum of these patients is the most helpful diagnostic tool for the assessment of the disease. The scientific progresses achieved in the last decades helped researchers and physicians to discover some of autoepitopes targeted by the autoantibodies, although the majority of them have not been identified yet. Additionally, the central nervous system is full of epitopes that cannot be found elsewhere in the human body, for this reason, autoantibodies that selectively target these epitopes might be used for the differential diagnosis between patients with and without the neuropsychiatric symptoms. In this review, the most relevant data is reported with regard to mechanisms implicated in the production of autoantibodies and the most important autoantibodies found among patients with systemic lupus erythematosus with and without the neuropsychiatric manifestations.

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.

16 α-Hydroxyestrone induced adduct generate high affinity autoantibodies in SLE

PURPOSE

Increased 16 α-hydroxyestrone (16 α-OHE₁) and autoantibodies against histone H1 (H₁) have been well described in systemic lupus erythematosus (SLE), but the combination effects of 16 α-OHE₁ and H₁ remains unclear. Here, we tried to assess the affinity and binding specificity of SLE autoantibodies against the 16 α-OHE₁-H₁ adduct. IgG was induced against this adduct and was also used as immunochemical probe for the estimation of 16 α-OHE₁ in the serum of SLE patients.

MATERIALS AND METHODS

The affinity and binding specificities of SLE autoantibodies against 16 α-OHE₁-H₁ were determined by direct binding and inhibition ELISA as well as quantitative precipitation titration in 60 patients and 30 control subjects.

RESULTS

Purified SLE autoantibodies showed greater recognition to 16 α-OHE₁-H₁ over H₁ (p < 0.05) or 16 α-OHE₁ (p < 0.001). The relative affinity of SLE autoantibodies for 16 α-OHE₁-H₁, H₁ and 16 α-OHE₁ was 1.41 × 10^-7, 1.31 × 10^-6, and 1.03 × 10^-6, respectively. The concentration of 16 α-OHE₁ in the sera of SLE patients was significantly higher than controls (p < 0.05) as estimated by anti-16 α-OHE₁-H₁ antibodies.

CONCLUSIONS

High affinity of 16 α-OHE₁-H₁ with SLE autoantibodies might suggest an antigenic role of this adduct in the production of these autoantibodies. The anti-16 α-OHE₁-H₁ antibody is a good immunochemical probe to measure 16 α-OHE₁ in different SLE sera.

High diagnostic accuracy of histone H4-IgG autoantibodies in systemic lupus erythematosus

Objective

Diagnosis of SLE relies on the detection of autoantibodies. We aimed to assess the diagnostic potential of histone H4 and H2A variant antibodies in SLE.

Methods

IgG-autoantibodies to histones H4 (HIST1H4A), H2A type 2-A (HIST2H2AA3) and H2A type 2-C (HIST2H2AC) were measured along with a standard antibody (SA) set including SSA, SSB, Sm, U1-RNP and RPLP2 in a multiplex magnetic microsphere-based assay in 153 SLE patients [85% female, 41 (13.5) years] and 81 healthy controls [77% female, 43.3 (12.4) years]. Receiver operating characteristic analysis was performed to assess diagnostic performance of individual markers. Logistic regression analysis was performed on a random split of samples to determine the additional value of histone antibodies in comparison with SA by likelihood ratio test and determination of diagnostic accuracy in the remaining validation samples.

Results

Microsphere-based assay showed good interclass correlation (mean 0.85, range 0.73-0.99) and diagnostic performance in receiver operating characteristic analysis (area under the curve (AUC) range 84.8-93.2) compared with routine assay for SA parameters. HIST1H4A-IgG was the marker with the best individual diagnostic performance for SLE vs healthy (AUC 0.97, sensitivity 95% at 90% specificity). HIST1H4A-IgG was an independent significant predictor for the diagnosis of SLE in multivariate modelling (P < 0.0001), and significantly improved prediction of SLE over SA parameters alone (residual deviance 45.9 vs 97.1, P = 4.3 × 10-11). Diagnostic accuracy in the training and validation samples was 89 and 86% for SA, and 95 and 89% with the addition of HIST1H4A-IgG.

Conclusion

HIST1H4A-IgG antibodies improve diagnostic accuracy for SLE vs healthy.

Combination of autoantibodies against different histone proteins influences complement-dependent phagocytosis of necrotic cell material by polymorphonuclear leukocytes in systemic lupus erythematosus

OBJECTIVE

Polymorphonuclear leukocytes (PMN) with autoantibody-coated engulfed necrotic cell material (NC) are frequently seen in systemic lupus erythematosus (SLE). We evaluated the roles of complement, different antihistone antibodies (anti-H ab), and oxidative burst in the phagocytosis of NC by PMN, as well as association to disease activity and clinical phenotype in SLE.

METHODS

ELISA and immunoblot were used to measure antibodies to different histone proteins in sera from patients with SLE and complement-deficient individuals. Phagocytosis of NC by PMN and oxidative burst activity was assessed by flow cytometry.

RESULTS

A clearly increased phagocytosis of NC was seen in patients with active SLE, which was associated with high levels of anti-H ab concentrations and oxidative burst activity. The complement system contributed to efficient phagocytosis of NC by PMN through activation of the classical pathway, and the phagocytosis was mediated by FcγRIIA, FcγRIIIB, and CR1 in combination. A pattern of high phagocytosis, consumption of classical pathway components, and a broad anti-H ab repertoire was seen particularly in patients with nephritis and serositis. The combination of antibodies to several different histone proteins, often with anti-DNA antibodies, promoted an efficient uptake of NC, whereas antibodies against only histone H1 or a few histones seemed to be of less importance.

CONCLUSION

The distributions of specificities among anti-H ab are of great importance in the complement-dependent phagocytosis of debris from NC in SLE. Measurement of anti-H ab could be useful in monitoring of this disease and contribute to improved understanding of the autoimmune process.

Nucleic acid-associated autoantigens: pathogenic involvement and therapeutic potential

Autoimmunity to ubiquitously expressed macromolecular nucleic acid-protein complexes such as the nucleosome or the spliceosome is a characteristic feature of systemic autoimmune diseases. Disease-specificity and/or association with clinical features of some of these autoimmune responses suggest pathogenic involvement which, however, has been proven in only a few cases so far. Although the mechanisms leading to autoimmunity against nucleic acid-containing complexes are still far from being fully understood, there is increasing experimental evidence that the nucleic acid component may act as a co-stimulator or adjuvans via activation of nucleic acid-binding receptor systems such as Toll-like receptors in antigen-presenting cells. Dysregulated apoptosis and inappropriate stimulation of nucleic acid-sensing receptors may lead to loss of tolerance against the protein components of such complexes, activation of autoreactive T cells and formation of autoantibodies. This has been demonstrated to occur in systemic lupus erythematosus and seems to represent a general mechanism that may be crucial for the development of systemic autoimmune diseases. This review provides a comprehensive overview of the most thoroughly-characterized nucleic acid-associated autoantigens, describing their structure and biological function, as well as the nature and pathogenic importance of the reactivities directed against them. Furthermore, recent advances in immunotherapy such as antigen-specific approaches targeted at nucleic acid-binding antigens are discussed.

Identification of autoantigens specific for systemic lupus erythematosus with central nervous system involvement

Using proteomic analysis, we identified candidate autoantigens specific for central nervous system (CNS) involvement in systemic lupus erythematosus (SLE). Proteins, extracted from cultured human neuroblastoma cells, were separated both by SDS-PAGE (1-DE) and two-dimensional electrophoresis (2-DE), and transferred to membranes. Western blot analysis was performed using serum samples from 30 SLE patients with CNS involvement (CNS-Lupus) and from 30 SLE patients without CNS involvement (non-CNS-SLE). The detected autoantigens were identified using MALDI-TOF/TOF MS. On the 1-DE Western blot, we detected 32 antigenic bands in the serum samples from the CNS-Lupus patients. Among them, four bands were detected significantly more frequently in the CNS-Lupus patients than in the non-CNS-SLE patients. Three bands were detected in four or more of the CNS-Lupus patients but in only one or none of the non-CNS-SLE patients. We thus selected these seven bands for the next investigations. Next, we detected protein spots corresponding to the selected seven bands by 2-DE Western blot and identified four proteins. They are peroxiredoxin-4, ubiquitin carboxyl-terminal hydrolase isozyme L1, splicing factor arginine/serine-rich 3, and histone H2A type 1. These four candidate autoantigens for the anti-neuronal cell antibodies would be a useful marker for CNS-Lupus.

RETRACTED: Drug-induced lupus erythematosus

Drug-induced lupus is a syndrome which share symptoms and laboratory characteristics with idiopathic systemic lupus erythematosus (SLE). The terms drug-induced lupus (DIL) and drug-induced lupus erythematosus (DILE) are preferred, but other ones are also used-drug-related lupus, lupus-like syndrome and lupus erythematosus medicamentosus. The first case of DILE was reported in 1945 and associated with sulfadiazine. In 1953, it was reported that DILE was related to the use of hydralazine. More than 80 drugs have been associated with DILE. The average age of patients with DILE is nearly twice that of patients with idiopathic SLE. Approximately half the patients with drug-induced SLE are women, compared with 90% of patients with idiopathic SLE. Similarly to idiopathic lupus, DILE can be divided into systemic, sub-acute cutaneous and chronic cutaneous lupus. The syndrome is characterised by arthralgia, myalgia, pleurisy, rash and fever in association with antinuclear antibodies in the serum. The clinical and laboratory manifestations of drug-induced SLE are similar to those of idiopathic SLE, but central nervous system and renal involvement are rare in DILE. Recognition of DILE is important because it usually reverts within a few weeks after stopping the drug. This review discusses the general issues in DILE, such as pathogenic mechanisms, clinical forms and diagnostic criteria, and provides more detailed information for some of the most recent implicated drugs: minocycline, statins, anti-TNF-alpha agents.

Involvement of autoimmunity against nuclear histone H1 in liver transplantation tolerance

BACKGROUND

Our recent studies suggested that anti-histone H1 autoantibody (auto-Ab) plays an important role in experimental and clinical liver allograft tolerance as a natural immunosuppressive factor. The present study aimed to explore how the autoimmune response against histone H1 is involved in tolerance induction.

METHODS

The measurement of anti-histone H1 auto-Ab and immunohistochemical analysis were performed in serum and liver allografts after orthotopic liver transplantation (OLT). To compare the auto-Ab response against histone H1 between the recipients of rejector (DA-LEW) and tolerogenic (DA-PVG) OLT models, naïve recipients were immunized with calf thymus histone H1. The immunosuppressive state of histone H1-immunized rats was assayed by mixed lymphocyte reaction (MLR).

RESULTS

Anti-histone H1 Ab titer was transiently increased during the rejection phase after OLT (days 7-21) in the DA-PVG combination, while no such response was confirmed in the DA-LEW acute rejection model. Nuclear histone H1 antigens were found in the cytoplasm and the extracellular environment in liver allografts at the rejection phase in the tolerogenic model but not in the rejector model, resulting from the transient induction of anti-histone H1 auto-Ab in recipient PVG rats after OLT. Low dose and short-term immunization with histone H1 upregulated the anti-histone H1 Ab titer in naïve PVG rats, which exhibited a low allogeneic immune response, while no such response was found in naïve LEW rats.

CONCLUSIONS

These results suggest that the sensitivity to nuclear antigens such as histone H1 may be a key factor determining the acceptance or rejection of donor liver grafts, at least in DA-PVG and DA-LEW combinations.

Anti-histones antibodies in systemic lupus erythematosus: prevalence and frequency in neuropsychiatric lupus

To investigate the specificity, sensitivity, and concomitant presence of antibodies against histones (H), histone H1 (H1), and histone H3 (H3) in patients with systemic lupus erythematosus (SLE) and analyze their association with SLE. Serum IgG anti-histones antibodies were detected by enzyme-linked immunosorbent assay in 144 SLE patients consisting of 24 neuropsychiatric lupus (NPSLE), 65 lupus nephritis (LN), and 55 SLE, 100 other rheumatic diseases patients, as well as 40 healthy controls. Clinical and biological parameters of the patients were also evaluated. Anti-H, anti-H1, and anti-H3 antibodies yielded a sensitivity of approximately 33% and a specificity of more than 93% for SLE, which was comparable to that found for anti-double-stranded DNA (anti-dsDNa) antibodies. More significantly, anti-histone antibody is found in approximately 50% of patients with NPSLE compared with LN. Moreover, the titers of anti-histones antibodies of NPSLE patients were significantly higher than that of patients with SLE and LN. The sequential analysis revealed a close correlation of anti-H and anti-H1 antibodies with SLE disease activity. There was an approximate 30% positive rate of anti-histones antibodies in 144 SLE patients lacking anti-nucleosome, anti-mDNA, anti-Sm, and anti-dsDNA antibodies. Antibodies to histones H1 and H3 are markers with high specificity of 93.6-96.4% for SLE. The anti-histone antibody markers are prevalent in approximately 50% of NPSLE. Furthermore, there was a strong correlation with SLE disease activity index and levels of antibodies to histones and H1.

Experimental and clinical significance of antinuclear antibodies in liver transplantation

Histone H1 and high-mobility group box 1 (HMGB1) proteins are known to initiate an immune reaction, and the corresponding antibodies (Abs) possess immunosuppressive activity. In the present study, we aimed to evaluate the immunological role of antinuclear Abs in experimental and clinical liver transplantation. In a rat tolerogenic orthotopic liver transplantation (OLT) model, antihistone H1 and HMGB1 titers were induced during the rejection and tolerance induction phases, respectively. Those Ab responses also were confirmed in a drug-induced tolerance model (acute rejection model + cyclosporin A [0 to 14 days after OLT]). We also found a similar tendency in our clinical drug-free patient (who experienced complete cessation of any immunosuppressive treatments) and that antinuclear Abs induced in the serum after cessation of immunosuppressants play a part of immune privilege in this patient. These results suggest that antinuclear Abs are important factors for overcoming rejection and the subsequent tolerance induction in liver transplantation.

Impact of vaccine therapy using nuclear histone H1 on allograft survival in experimental organ transplantation

BACKGROUND

We recently reported that autoreactive antibody (Ab) against nuclear histone H1 had been identified as an immunosuppressive factor in a rat tolerogenic orthotopic liver transplantation (OLT) model. The present study aimed to determine whether the up-regulation of antihistone H1 Ab by histone H1 vaccination leads to tolerance.

METHODS

Histone H1-immunized rats were established by intraperitoneal vaccination with histone H1 at every two-weekly interval. By using mixed lymphocyte reaction (MLR) and heterotopic heart transplantation (HHT), the alloreactive T cell response and allograft survival of histone H1-immunized rats were compared with those of control rats. Cytokine and cellular profiles in histone H1-immunized rats were determined by reverse transcriptase polymerase chain reaction (RT-PCR), enzyme-linked immunosorbent assay (ELISA) and flow cytometry.

RESULTS

Immunization with histone H1 in Freund's adjuvant induced alloreactive T cell unresponsiveness and prolonged heterotopic heart allograft survival. It also down-regulated the expression of major histocompatibility complex (MHC) class II and CD25 on splenic cells, elevated the T helper cell type 2 (Th2) skewing index (Interleukin (IL)-4/interferon (IFN)-gamma ratio or IL-4/IL-2 ratio) and modified the serum cytokine profiles.

CONCLUSIONS

The present results suggest that histone H1 vaccination of transplant recipients, which leads to the production of immunosuppressive factor and the modification of the cytokine/cellular profiles, has great potential as a tolerance therapy for prospective transplantation.

[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.

Circulating anti-retinal antibodies as immune markers in age-related macular degeneration

Age-related macular maculopathy (ARM) and age-related macular degeneration (AMD) are the leading causes of blindness in the Western world. Despite the magnitude of this clinical problem, very little is known about the pathogenesis of the disease. In this study, we analysed the sera (using indirect immunohistochemistry and Western blot analysis) from a very large cohort of such patients and normal age-matched controls to detect circulating anti-retinal antibodies. Patients with bilateral drusen (n = 64) and with chorioretinal neovascularization (CNV) (n = 51) were recruited in addition to age-matched control subjects (n = 39). The sera were analysed for anti-retinal immunoglobulins on retinal sections. The data were then correlated with the clinical features graded according to the International Classification and Grading System of ARM and AMD. The sera of patients with drusen (93.75%) and CNV (82.27%) were found to have a significantly (P = 0.02) higher titre of autoantibodies to the retina in comparison with controls (8.69%), indicating significant evidence of involvement of the immune process in early stages of AMD. Subsequent statistical analysis of the drusen group showed significant progressive staining (P = 0.0009) in the nuclei layers from early to late stages of ARM. Western blotting confirmed the presence of anti-retinal immunoglobulins to retinal antigens. As anti-retinal immunoglobulins are present in patients with bilateral drusen and exudative AMD, these antibodies could play a significant role in the pathogenesis of AMD. Whilst we do not have evidence that these antibodies precede disease onset, the possibility that their presence might contribute to disease progression needs to be investigated. Finally, the eventual identification of the target antigens detected by these antibodies may permit the future development of new diagnostic methods for ARM and AMD.

Over-expression of TATA binding protein (TBP) and p53 and autoantibodies to these antigens are features of systemic sclerosis, systemic lupus erythematosus and overlap syndromes

The aim of this study was to determine the expression levels of p53 and TATA binding protein (TBP) and the presence of autoantibodies to these antigens in Asian Indian patients with systemic sclerosis (SSc), overlap syndromes (OS) and systemic lupus erythematosus (SLE). Fifty patients with SSc, 20 with OS, including mixed connective tissue diseases (MCTD), 20 with SLE, 10 disease controls (DC) and 25 controls (C) were studied. The over-expression of p53 and TBP antigen was determined quantitatively by sandwich enzyme-linked immunosorbent assay (ELISA), varies between four- and sevenfold higher in patients with SSc, OS and SLE, in comparison to DC and C. The expressed protein antigens were not present as free antigens but as immune-complexes. Autoantibodies to p53 were detected by ELISA in 78% subjects with SSc, 100% with OS and 80% with SLE. Autoantibodies to TBP were observed in 28% patients with SSc, 25% with OS and 15% with SLE. In comparison to healthy controls, the titre of antibodies to p53 was significantly higher in patients with SSc (P = 0.00001) than the patients with OS (P = 0.00279) and SLE (P = 0.00289), whereas the titre of antibodies to TBP was higher in patients with OS (P = 0.00185) than the SLE (P = 0.00673) and the SSc (P = 0.00986) patients. Autoantibodies to p53 and TBP were detected in all these patients and the levels of these two autoantibodies showed weak negative correlation with each other. We propose that the over-expression of these antigens might be due to hyperactive regulatory regions in the p53 and TBP gene.

LIVER TRANSPLANTATION-INDUCED ANTIHISTONE H1 AUTOANTIBODIES SUPPRESS MIXED LYMPHOCYTE REACTION

BACKGROUND

In a rat model of orthotopic liver transplantation (OLT), recipient serum after OLT (post-OLT serum) has been reported to prevent allograft rejection. However, the molecular identities of immunosuppressive factors, which are in the early stage of post-OLT, remain elusive. This study was aimed to identify immunodominant suppressive factors present in early post-OLT serum.

METHODS

The immunosuppressive activities of post-OLT serum, immunoglobulin (Ig) G-depleted serum, and purified IgG were evaluated in vitro by inhibition of the mixed lymphocyte reaction (MLR). Autoantigens recognized by the MLR-inhibitory IgG in early post-OLT serum were identified by the internal protein sequencing.

RESULTS

Recipient post-OLT serum inhibited MLR, and its immunosuppressive activity vanished by means of the elimination of OLT-inducible IgG. IgG from post-OLT sera (2-3 weeks) specifically reacted to 31-, 34-, and 73-kDa autoantigens on splenic cells. The internal sequences of the doublet 31- and 34-kDa antigens coincided completely with those of histone H1 molecules. The levels of histone H1-specific antibodies were transiently increased to a plateau around 2 to 3 weeks after OLT but decreased in the later tolerogenic phase. Immunodepletion of antihistone H1 autoantibodies from early post-OLT serum abolished the MLR-inhibitory activity. Furthermore, rabbit polyclonal antibody-directed histone H1 not only suppressed MLR but also prolonged allograft survival.

CONCLUSIONS

In this article, the authors provide evidence that autoreactive antibodies against histone H1, which are transiently induced at the early stage by liver transplantation, are a major OLT-induced graft survival factor.

Somatic mutations to arginine residues affect the binding of human monoclonal antibodies to DNA, histones, SmD and Ro antigen

Autoantibodies to a wide variety of antigens are associated with systemic lupus erythematosus (SLE). Antibodies to double-stranded DNA (anti-dsDNA) are thought to be particularly closely related to tissue damage and disease activity in SLE. Autoantibodies to histones, Sm and Ro are found in patients with SLE, but their role in pathogenesis is unclear. Using a transient expression system, we previously showed that particular sequence motifs in CDRs of light chains derived from the human Vlambda gene 2a2 are very important in determining their ability to form a DNA-binding site, when paired with the heavy chain of the human monoclonal anti-dsDNA antibody B3. These motifs are often sites of somatic mutation and/or contain arginine residues. In the experiments reported in this paper, the same expression system was used to show that these CDR motifs also affect binding to histones, Ro antigen and Sm antigen, but that binding to different antigens is affected in diverse ways by particular changes in the sequence of the CDRs. The heavy chain also plays a role in binding to these antigens. Pairing of the same range of 11 2a2 derived light chains with the heavy chain of a different anti-DNA antibody, 33.H11, gave reduced ability to bind DNA in comparison with the results obtained using the B3 heavy chain. Computer-generated models of the three-dimensional structures of these heavy/light chain combinations were used to define the positions occupied by the important sequence motifs at the binding sites of these antibodies, and to explain the different effects exerted by arginine residues at different positions in the light chains.

The autoimmune response to chromatin antigens in systemic lupus erythematosus: autoantibodies against histone H1 are a highly specific marker for SLE associated with increased disease activity

This study investigates specificity, sensitivity and concomitant presence of antibodies against histone H1 (H1), nucleosomes (NUC), chromatin (CHR) and dsDNA in patients with systemic lupus erythematosus (SLE), analyses their association with SLE disease activity and characterizes the immunodominant epitope reactivity of anti-H1 antibodies and its relation to SLE disease activity. In a cross-sectional study 394 sera of patients with various rheumatic diseases and healthy subjects were analysed by ELISA for antibodies against H1, NUC, CHR and dsDNA. In addition, a longitudinal analysis was performed that included 121 sequential serum samples derived from 16 SLE patients to assess the relation of these antibodies as well as antibodies to histone H2B to SLE disease activity. To assess epitope reactivity of anti-H1 antibodies overlapping synthetic peptides covering the entire H1 sequence were used. Anti-H1 antibodies yielded a sensitivity of approximately 45% and a specificity of over 98% for SLE, which was comparable to that found for anti-dsDNA antibodies. Anti-CHR and anti-NUC antibodies were of similar sensitivity but slightly (anti-CHR) or considerably (anti-NUC) less specific for SLE (95 and 85%, respectively). The sequential analysis revealed a strong correlation of anti-H1 antibodies with SLE disease activity that was better than the correlation of anti-dsDNA and anti-NUC antibodies, while only weak correlation was found for anti-CHR and anti-H2B antibodies. The immunodominant epitope for anti-HI was localised between amino acids 204 and 218 (pp204-218) and immune reactivity to this epitope also correlated with disease activity. Anti-H1 is a highly specific marker for SLE with a diagnostic value comparable to anti-dsDNA. A positive testing for anti-H1 indicates increased disease activity, as does the appearance of antibodies to its immunodominant epitope pp204-218.

Immunoscreening of phage-displayed cDNA-encoded polypeptides identifies B cell targets in autoimmune disease

Characterisation of self-antigens can contribute to an understanding of the aetiology of autoimmune disorders as well as to the development of new therapies and diagnostic methods. The present study was undertaken to investigate the applicability of complementary DNA (cDNA) phage-display technology to the identification of autoantigens recognised by the humoral response in autoimmune disease. Using systemic lupus erythematosus (SLE) as a model system, a pool of patient immunoglobulin G (IgG) was biopanned on a fibroblast cDNA phage-display library constructed in the vector pJuFo. Following three rounds of biopanning, recovered cDNAs were sequenced and then identified using BLAST comparisons with international databases. Both previously reported SLE autoantigens, for example, alpha-enolase and U1 small nuclear ribonucleoprotein-C (U1snRNP-C), and novel autoantibody targets, including ribosomal protein S20 (RPS20), ribosomal protein S13 (RPS13), ubiquitin-like protein PIC1 (PIC1), and transcription factor-like protein MRG15 (MRG15), were recovered from the biopanning procedure. Radiobinding assays were used subsequently to confirm the reactivity of some putative autoantigens to panels of sera from SLE patients, control patient groups, and healthy individuals. SLE patient sera were positive for reactivity to: U1snRNP-C, 4/15 (27%); alpha-enolase, 1/15 (7%); RPS20, 3/15 (20%); RPS13, 1/15 (7%); PIC1, 1/15 (7%); and MRG15, 2/15 (13%). Overall, cDNA phage-display technology appears to be applicable to the identification of autoantigens in autoimmune disease.

Idiosyncratic drug reactions: the reactive metabolite syndromes

Idiosyncratic drug reactions are unpredictable reactions that can result in significant morbidity and mortality. Severe reactions are often characterised by fever and internal organ involvement. Despite progress in the identification of reactive metabolites believed to be the cause of idiosyncratic reactions, the basic mechanisms remain elusive. Furthermore, because of the lack of consensus regarding definition of these syndromes, reporting, and therefore epidemiological data, are often unreliable. Research is needed to explore further the pathophysiology of these reactions, so that better diagnostic tests and treatment methods can be developed.

Prevalence and antigen specificity of anti-histone antibodies in patients with polymyositis/dermatomyositis

Anti-histone antibodies have been detected in the sera of patients with various autoimmune diseases. The existence of anti-histone antibodies in patients with polymyositis/dermatomyositis, however, has not been reported. We found anti-histone antibodies in eight (17%) of 46 sera from patients with polymyositis/dermatomyositis by an enzyme-linked immunosorbent assay. One serum was positive for both IgG anti-histone antibodies and IgM anti-histone antibodies. Six sera were positive only for IgG anti-histone antibodies. One serum was positive only for IgM anti-histone antibodies. An indirect immunofluorescence analysis using HEp-2 cells as the substrate showed that all sera positive for anti-histone antibodies produced homogeneous nuclear fluorescence. This immunofluorescence pattern disappeared after absorption of anti-histone activity with total histones. An immunoblotting analysis demonstrated that the anti-histone antibodies were predominantly directed against histone H1 in all seven sera with IgG anti-histone antibodies. Weak reactivity with H2B and H4 were also found in three sera from the patients with polymyositis/dermatomyositis. Sera from two patients with polymyositis/dermatomyositis displayed anti-H2A and H3 activity. One of the two sera showed IgM anti-histone antibodies in the enzyme-linked immunosorbent assay reacted with H1, H2A, H2B, H3, and H4, whereas the other serum reacted with no fractions of total histones. The activity of anti-histone antibodies disappeared in immunoblotting after absorption with total histones. All of the patients with anti-histone antibodies were free from lung fibrosis or internal malignancies. Thus, our data indicate that the presence of anti-histone antibodies is classified as one of the serologic abnormalities observed in polymyositis/dermatomyositis.

Identification and characterization of a calreticulin-binding nuclear protein as histone (H1), an autoantigen in systemic lupus erythematosus

Our objective was to identify nuclear calreticulin-binding protein(s) and investigate whether there is a correlation between presence of autoantibodies against calreticulin and calreticulin-binding protein(s) in the sera of patients suffering from systemic lupus erythematosus (SLE). The ligand overlay procedure using digoxigenin-labelled calreticulin was used to identify a calreticulin-binding protein in the nuclear fraction of bovine brain. Fractionation of the nuclear components was used to localize the major positive calreticulin-binding protein. The protein was partially purified using hydroxylapatitie chromatography and subjected to NH2-amino acid sequence analysis. Immunoblots using the sera of SLE patients were then carried out on calreticulin and the calreticulin-binding protein. The calreticulin-binding protein present in the nucleoplasm was identified as histone H1. Approximately 62% (26/42) patients with SLE had IgG antibodies directed against H1 whereas the sera of healthy individuals did not react with the antigen; 36% of patients with SLE had both anti-calreticulin and anti-histone H1 antibodies. Phosphorylation of the latter protein did not alter its immunoreactivity. These findings demonstrate that the concomitant presence of autoantibodies directed against both calreticulin and histone H1 occurs frequently in patients with SLE and may help shed some light on the mechanisms which bring about the autoimmune response.

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.

Characterization of anti-histone antibodies in patients with type 1 autoimmune hepatitis

We have recently found that antibodies to total histones are common in a group of American patients with type 1 autoimmune hepatitis (AIH). In an attempt to determine the profile and clinical association of anti-histone antibody (AHA), 45 Japanese AIH patients were studied for serum isotypic reactivity with individual histones (H1, H2A, H2B, H3, H4) by enzyme-linked immunosorbent assay and western blotting. The results revealed that 40% of sera had reactivities with at least one of individual histones and that the antibodies were detected in all three classes of immunoglobulins (IgG, IgM, IgA). Immunoglobulin G type anti-H3 showed the dominant reactivity and it characterized 72% of sera with AHA. The titre of anti-H3 decreased significantly (P < 0.0075) after steroid therapy and the index of decrease for anti-H3 was correlated in individuals with that for serum aminotransferase. In general, patients with AHA showed higher serum level of alanine aminotransferase (P < 0.05), immunoglobulin G (P < 0.025), and higher frequency of A2-DR4 haplotype (53 vs 17%) than their seronegative counterparts. However, the titre of AHA was low in this disease condition and histone class-specific antibodies did not distinguish patients with distinctive clinical features, although patients with anti-H3 tended to be younger than those without AHA.

Circulating plasma levels of nucleosomes in patients with systemic lupus erythematosus: correlation with serum antinucleosome antibody titers and absence of clear association with disease activity

OBJECTIVE

To assess nucleosome plasma levels in patients with systemic lupus erythematosus (SLE) and to study the correlations with serum antinucleosome, anti-double-stranded DNA (anti-dsDNA), and antihistone antibody activities, as well as with disease activity (by the SLE Disease Activity Index [SLEDAI]).

METHODS

In a cross-sectional study, we assessed 58 SLE patients for their plasma nucleosome levels. Plasma nucleosome levels as well as serum antinucleosome, anti-double-stranded DNA, and antihistone antibody activities were assessed by enzyme-linked immunosorbent assay. SLE activity was evaluated using the SLEDAI:

RESULTS

The mean (+/-SD) plasma nucleosome concentration in SLE patients was 52 +/- 159 ng/ml (range 5-1,180), and was significantly higher than that of the controls (16 +/- 8.8 ng/ml, range 8-52; P = 0.03). Thirteen of the 58 lupus patients had levels over the range of normal (defined as the control mean + 3 SD, or 42 ng/ml). An inverse correlation was found between nucleosome plasma levels and serum antinucleosome antibody activity in the entire group of SLE patients, those with active disease, and those with inactive disease, respectively. No correlation was found between the SLEDAI and nucleosome plasma concentrations.

CONCLUSION

Nucleosome plasma levels may be normal or increased in SLE, and found in patients with active or inactive SLE. Longitudinal studies are needed to further establish whether high levels of circulating nucleosomes may predict the occurrence of an SLE flare.

Analysis and significance of anti-nuclear antibodies in dogs

Assays for detecting and measuring antinuclear antibodies (ANA) in dogs were compared. They included the indirect immunofluorescence test, using rat liver as substrate, and ELISAs for three nuclear antigens: double-stranded DNA, single-stranded DNA, and histone. There was no correlation between the ANA titre and antibodies to the three nuclear antigens. Analysis of ANA in different arthropathies showed no specific disease association. HEP-2 cells showed no fluorescence reaction with either ANA-positive or ANA-negative dog sera. Western blotting produced too complex a pattern to identify specific antigens. The antigens that reacted with ANA in dogs were not identified; there is either a broad range of reactivities or non-specific binding of immunoglobulins.

Specificities and genetic characteristics of nucleosome-reactive antibodies from autoimmune mice

Antinuclear antibodies are present in the serum of individuals with systemic autoimmune diseases such as SLE. Most autoantibodies characterized to date are directed against isolated nuclear molecules such as DNA or histones. We have obtained from spontaneously autoimmune mice six IgG mAb that recognize conformational nucleosome epitopes, but do not react with individual histones or DNA. For three of these mAb, the epitope is at least partially present in the H2A-H2B-DNA nucleosome subparticle, although their binding characteristics differ from those of conventional anti-H2A-H2B-DNA antibodies. All six mAb use VH or Vkappa genes which are recurrently utilized in anti-DNA and other antinuclear antibodies. The V regions of the nucleosome-reactive mAb also contain charged (mostly cationic) residues at sites that are likely to be critical for interaction with nucleosomal antigens. These results suggest that the usage of certain V gene segments in conjunction with suitable V(D)J rearrangements may confer reactivity to nucleosomal antigens. B cells producing such autoantibodies are probably expanded early during the autoimmune process. Somatic mutations in the V regions of nucleosome-reactive mAb may modulate their specificities and result in the acquisition of binding patterns restricted to individual chromatin components such as DNA.

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.

Drug-induced lupus

Drug-induced lupus is a syndrome resembling mild systemic lupus erythematosus which can complicate treatment with certain apparently unrelated therapies. The most common individual agents are procainamide and hydralazine. Drugs less frequently associated with the disease are chlorpromazine, isoniazid, methyldopa, penicillamine, quinidine and sulfasalazine. Whole drug groups have also been implicated, such as the anticonvulsants, beta-blockers, sulfonamides and some of the newer 'biological' agents. The syndrome is characterised by arthralgia, myalgia, pleurisy, rashes and fever in association with antinuclear antibodies in the serum. More serious features of idiopathic lupus such as nephritis and cerebral disease are rare in drug-induced disease. The pathogenesis is unknown but in some cases is thought to be due to interactions between the drug and DNA or histones, rendering them immunogenic. For the biological agents, including interferons and antibodies to tumour necrosis factor-alpha, it has been suggested that it is due to disruption of the cytokine network. Although extremely rare, recognition of drug-induced lupus is important because it reverts within a few weeks of stopping the drug. It is possible that understanding its pathogenesis may shed light on its more serious relative, systemic lupus erythematosus.

Serological markers of disease activity in systemic lupus erythematosus

When measured serially by Farr assay at a frequency of approximately once a month, changes in levels of anti-dsDNA appear to be a good predictor of clinical disease activity. Although the role of antibodies to the RNA component of snRNP awaits further studies, measurement of anti-UsnRNP antibody levels seems to be of limited value in monitoring lupus patients in clinical practice. The same holds for antibodies to SSA (Ro) and anti-histone antibodies. More recently described antibodies to C1q are probably useful in the follow-up of SLE patients suspected of proliferative renal involvement. The best alternative to measuring levels of the antibodies mentioned before is probably serial analysis of activation of the complement cascade. Levels of complement factors like C3, C4 and, functionally, CH50 remain a useful parameter for monitoring disease activity in SLE, although fluctuations in anti-dsDNA as measured by Farr assay seem superior with respect to sensitivity and specificity for an ensuing relapse. Despite the problems in sampling, measuring levels of activated split products of complement factors like C3a, C3d or C5a may prove to be a valuable tool in the follow-up of lupus patients. The involvement of the endothelial surface is illustrated by rising sVCAM-1 levels prior to relapses in SLE. Although one could expect that subsequent inflammation should be reflected by increased levels of inflammatory molecules like CRP and IL-6, the use of these molecules as predictors of lupus activity seems limited. Interferon-alpha as a direct reflector of the effector phase seems, however, rather promising in this respect and awaits longitudinal studies to analyse the possible relation with clinical disease activity and other serological parameters.

Clinical characteristics associated with antihistone antibodies in patients with localized scleroderma

BACKGROUND

Recently we demonstrated the presence of antihistone antibodies (AHA) in localized scleroderma.

OBJECTIVE

Our purpose was to determine clinical characteristics associated with AHA in patients with localized scleroderma.

METHODS

We examined 57 serum samples by an enzyme-linked immunosorbent assay in the following three subgroups: 15 patients with generalized morphea, 27 with linear scleroderma, and 15 with morphea. We classified the patients as having generalized morphea when they had four or more lesions on at least two areas of the body, irrespective of whether the lesions were of morphea or linear type.

RESULTS

AHA were detected in 42% of patients with localized scleroderma (24 of 57), and in 87% of patients with generalized morphea (13 of 15). The presence of AHA strongly correlated with the number of morphea lesions, the total number of lesions, and the number of involved areas of the body. However, AHA did not correlate with the presence or number of linear lesions. The presence of AHA showed a 87% sensitivity (13 of 15 patients) and a 74% specificity (31 of 42 patients) for generalized morphea.

CONCLUSION

Our data suggest that AHA are a serologic marker for generalized morphea and that the validity of our new classification for generalized morphea is supported by the high frequency of AHA detection.

Antihistone antibodies in systemic sclerosis. Association with pulmonary fibrosis

OBJECTIVE

To determine the prevalence and clinical significance of antihistone antibodies (AHA) in systemic sclerosis (SSc).

METHODS

Serum samples from patients with limited cutaneous SSc (n = 44), diffuse cutaneous SSc (dcSSc; n = 48), and other SSc-related disorders (n = 22) were examined by enzyme-linked immunosorbent assay and immunoblotting for AHA.

RESULTS

AHA were demonstrated in 29% of the 92 SSc patients and in 44% of those with dcSSc. The presence of AHA correlated with severe pulmonary fibrosis in those with dcSSc. Immunoblotting revealed that the predominant antigen was histone H1.

CONCLUSION

AHA might be a serologic indicator of the severity of pulmonary fibrosis in SSc.

Inhibition of histone/anti-histone reactivity by histone-binding serum components; differential effect on anti-H1 versus anti-H2B antibodies

IgG fractions were purified on a protein G-agarose column from sera of both systemic lupus erythematosus (SLE) patients and healthy donors. All IgG fractions, after elution with 0.5 M acetic acid, reacted with histones in an anti-histone ELISA assay, and IgG anti-histone activity was in all instances higher in the IgG fraction than in the corresponding whole serum. This was shown to be due to the presence in serum of histone-binding components that inhibited IgG binding to histones. Both normal human and SLE patients' sera had these histone-binding components, and disparity between serum-positive and -negative anti-histone antibody (AHA) tests was not dependent on differences in the blocking capacity but on IgG antibody levels and avidity. Interaction of normal serum IgG fraction with all five histones was of low avidity, whereas interaction of IgG from AHA-positive SLE sera with both H1 and H2B had high avidity. Low-affinity antibodies to every histone fraction, but also high-affinity anti-H1 antibodies, were preferentially inhibited. Our data indicate that several serum protein components are inhibiting histone/anti-histone interaction and may play a protective role against both high-affinity anti-H1 antibodies present in SLE patients, and natural, low-affinity, anti-histone antibodies. As some acute phase proteins, notably C-reactive protein, bind to histones, it is conceivable that they play such a role. High-affinity anti-H2B antibodies, present in some SLE patients, and not inhibited by these serum components, may, on the other hand, participate in the pathogenesis of the disease.

Evidence that a putative anti-idiotypic monoclonal antibody may actually be recognizing circulating immune complexes

Murine monoclonal antibodies (mAb) reacting with affinity-purified antihistone antibodies (AHA) from serum of a patient with systemic lupus erythematosus (SLE) were obtained. One of them, 8B3, was initially considered to recognize idiotypic (Id) determinants in AHA since (a) it reacted with AHA but not with control IgG; (b) this reactivity could be inhibited using affinity-purified AHA, but not with control IgG or whole serum; (c) affinity-isolated 8B3+ antibodies showed antihistone activity and not other activities tested so far; (d) antihistone activity due to 8B3+, but not that of 8B3- from the same serum, could be fully inhibited by the presence of 8B3 mAb in the antihistone assay and (e) serum levels of 8B3 reactivity were higher than normal in SLE patients with AHA (56%), in contrast with SLE patients without AHA (6%). From these results it was deduced that 8B3 defined a cross-reactive Id shared by a subset of AHA in SLE patients. However, the present results suggest that (a) 8B3 mAb did not recognize AHA or Ig, but did recognize a 55 kDa histone-binding protein; (b) this 55 kDa protein was present free at low concentration in all human sera, but also associated with IgG in 8B3+ SLE sera and (c) these complexes are responsible for the false positive results in the antihistone assay as shown for DNA/anti-DNA complexes. Thus, mAbs recognizing the non-Ig moiety of circulating immune complexes may resemble anti-Id antibodies with features of the so-called epibodies. These immune complexes may be responsible for false positive results and caution should be exercised in the interpretation of results.

Canine systemic lupus erythematosus. I: A study of 75 cases

We studied 75 cases of canine systemic lupus erythematosus (SLE) presenting with at least four criteria of the American Rheumatism Association (ARA), including antinuclear antibodies (ANAb). This disease mainly affects male German shepherds of an average age of 5 years. The most common clinical signs are polyarthritis (91% of cases), and renal (65%) and cutaneo-mucous disorders (60%). Hemolytic anemia is rare (13%). ANAb are present, often at high levels (> 256 up to 10(6) by indirect immunofluorescence on mouse blood smears). The titers are correlated with the severity and the stage of the disease. As double-stranded DNA Ab are rare and as antihistone Ab are frequent, the former could be replaced by the latter in the ARA criteria applied to the SLE dog. Another category of ANAb, named anti-type 1, also seems useful in diagnosing canine SLE. As for therapy, long-term remissions (up to 9 years without treatment) were obtained in 55.6% of 27 SLE dogs treated by levamisole. At first, levamisole was associated with induction corticotherapy, then administered alone and finally discontinued. Side effects were uncommon and transient.

Genetic association between natural autoantibody responses to histones and DNA in murine lupus

Genetic regulation of the spontaneous anti-histone antibody production in systemic lupus erythematosus (SLE) was studied using the H-2-congenic and T cell receptor beta chain gene complex (TCR beta)-congenic NZB and NZW strains and their crosses. We found that the original, parental H-2d/d NZB mice produced significantly higher titers of serum IgM class anti-histone antibodies than did the congenic H-2d/z or H-2z/z NZB mice. However, none of these three NZB strains produced IgG antibodies. The NZW strain of any H-2 haplotype did not produce IgM and IgG anti-histone antibodies. The IgG anti-histone antibodies were produced only by H-2d/z heterozygous NZB x NZW F1, but not by homozygous H-2z/z or H-2d/d NZB x NZW F1 mice. In studies using (NZB x NZW) F1 x NZB backcross mice, only the progeny having both H-2d/z and NZW-type TCR beta genotypes produced high amounts of IgG antibodies. There was a tight linkage between the NZW-type TCR beta and the production of IgG anti-histone antibodies in TCR beta-congenic NZB x NZW F1 mice. All these findings were in keeping with our preceding observations on the genetic regulation of anti-DNA antibodies in these mice and suggest that certain common mechanisms such as super-antigen-mediated or common idiotope-mediated regulations may underlie the production of these two distinct autoantibodies in NZB x NZW F1 mice.