Rabbit anti-HMG-17 antibodies recognize similar epitopes on the HMG-17 molecule as lupus autoantibodies. Relation with histone H1 defined epitopes.

HMG-17 is a nucleosomal protein which is an immune target of autoantibodies in systemic lupus erythematosus (SLE) and other autoimmune diseases. Autoantibody production in SLE is believed to result from autoantigen specific immune stimulation and subsequently, it is expected that antigenic determinants recognized by SLE autoantibodies and induced antibodies by immunization are quite similar. To examine this issue, rabbits were immunized with purified HMG-17. The produced antiserum showed cross reactivity on blots and in inhibition ELISA with histone H1, even after its affinity purification with immobilized HMG-17. Finally, purification of the antiserum over H1 absorbed on nitrocellulose membrane produced specific anti-HMG-17 antibodies in the supernatant and anti-HMG-17/H1 antibodies that were bound to H1. SLE sera positive for HMG-17 had also cross reactivity with H1, and following the same procedure as before we received HMG-17 specific SLE autoantibodies and anti-HMG-17/H1 autoantibodies. Using the multipin epitope mapping technology, 19 overlapping 15-mer HMG-17 peptides and six 15-peptides, corresponding to known epitopes of histone H1, were synthesized. Four major epitopes were identified on the HMG-17 molecule, reactive with induced anti-HMG-17 antibodies, and these were the same as major autoepitopes In SLE. The sequence 25-51 of HMG-17, part of its DNA-binding domain, was recognized by the anti-HMG-17/H1 antibodies that were bound to H1. These antibodies recognized also defined epitopes of H1. Our results show that SLE autoantibodies can be directed against the same or similar epitopes as do IgGs evoked during the active immunization of animals, and provide additional evidence that autosensitization with an autoantigen might be operative. The possibility that the same or similar epitopes are found on different molecules (in this study HMG-17 and H1) supports the fact that there are rules by which nature selects the most dominant immunodeterminant to a given protein, which often represents functional or structural sites in the autoantigen.     

Lupus IgG VH4.34 antibodies bind to a 220-kDa glycoform of CD45/B220 on the surface of human B lymphocytes

Anti-lymphocyte autoantibodies are a well-recognized component of the autoimmune repertoire in human systemic lupus erythematosus (SLE) and have been postulated to have pathogenic consequences. Early studies indicated that IgM anti-lymphocyte autoantibodies mainly recognized T cells and identified CD45, a protein tyrosine phosphatase of central significance in the modulation of lymphocyte function, as the main antigenic target on T cells. However, more recent work indicates that lupus autoantibodies can also recognize B cells and that CD45 may also represent their antigenic target. In particular, IgM Abs encoded by V(H)4.34 appear to have special tropism for B cells, and strong, but indirect evidence suggests that they may recognize a B cell-specific CD45 isoform. Because V(H)4.34 Abs are greatly expanded in SLE, in the present study we investigated the antigenic reactivity of lupus sera V(H)4.34 IgG Abs and addressed their contribution to the anti-lymphocyte autoantibody repertoire in this disease. Our biochemical studies conclusively demonstrate that lupus IgG V(H)4.34 Abs target a developmentally regulated B220-specific glycoform of CD45, and more specifically, an N-linked N-acetyllactosamine determinant preferentially expressed on naive B cells that is sterically masked by sialic acid on B220-positive memory B cells. Strikingly, our data also indicate that this reactivity in SLE sera is restricted to V(H)4.34 Abs and can be eliminated by depleting these Abs. Overall, our data indicate that V(H)4.34 Abs represent a major component of the lupus IgG autoantibody repertoire and suggest that the carbohydrate moiety they recognize may act as a selecting Ag in SLE.     

Anti-histone antibodies in idiopathic and drug-induced lupus recognize distinct intrahistone regions

We have identified regions within core histones that are antigenic for autoantibodies in systemic lupus erythematosus (SLE) and drug-induced lupus. An immunoblotting technique was used to determine the reactivity of lupus antibodies for intact histones and for trypsin-resistant histone fragments that lack the amino- and carboxyl-terminal amino acids that are normally exposed in native nucleosomes. In SLE, the predominant anti-histone response was restricted to epitopes in the trypsin-sensitive regions. Of 20 SLE sera that had strong antibody activity for multiple intact histones, 17 showed minimal activity with any of the corresponding trypsin-resistant fragments. A markedly different pattern of reactivity was present in sera of patients with procainamide (Pr)-induced lupus in which antibodies to H2A, H2B, and the H2A-H2B complex had strong fragment activity. Interestingly, recognition of trypsin-resistant fragments was also noted in a small number of SLE sera that contained antibodies to the H2A-H2B complex. In contrast to both SLE and Pr-induced lupus, antibodies induced by hydralazine (Hy) reacted primarily with H3 and H4. Furthermore, these antibodies bound equally well to the corresponding trypsin-resistant regions that are thought to be relatively unexposed in native nucleosomes. Thus, the specificities of anti-histone antibodies in SLE, Pr-induced lupus, and Hy-induced lupus are markedly different, but in each disease reactivity appears to be restricted to a limited number of histone determinants. The data raise the possibility that autoantigen in the form of native nucleosomes may be recognized in SLE and possibly in Pr-induced lupus. In contrast, the propensity of Hy to induce autoantibodies to determinants usually not recognized in SLE or Pr-induced lupus may suggest a different immunogenic stimulus in this disease.     

Carbohydrate specificity of IgM autoantibodies to CD45 in Systemic Lupus Erythematosus

Patients with SLE develop IgM autoantibodies to different isoforms of CD45, the major surface membrane protein tyrosine phosphatase on lymphocytes and other nucleated hemopoietic cells. Because such autoantibodies could have a potential role in the development of immune dysfunction in this disorder, we performed a series of experiments to characterize their antigenic specificity further. Blots of recombinantE. coli fusion proteins encoded by exons 3–7 of the p220 and p180 isoforms were uniformly non-reactive with SLE IgM, suggesting that anti-CD45 autoantibodies in SLE are directed against conformational and/or carbohydrate epitopes, rather than linear polypeptide epitopes. This issue was examined further using chemically and enzymatically modified CD45 purified from T cells by lectin affinity chromatography as substrates. Treatment of CD45 with 25 mM sodium-m-periodate, sufficient to abrogate binding to various lectins, abolished the reactivity with SLE anti-CD45 autoantibodies. On the other hand, digestion of CD45 with neuraminidase enhanced the binding of anti-CD45 autoantibodies from some of the SLE sera. This result probably reflects decreased steric hindrance or charge repulsion because the binding of mouse monoclonal antibodies directed against linear polypeptide epitopes of CD45 was similarly enhanced. Digestion of CD45 with N-glycosidase F had no effect on autoantibody staining. Taken together, these data suggest that IgM anti-CD45 autoantibodies in SLE recognize non-sialylated carbohydrate determinants in the highly O-glycosylated polymorphic domains of CD45.Abbreviations SLE systemic lupus erythematosus - SBA soybean agglutinin - RCAI Ricinus communis agglutinin - SNL Sambucus nigra lectin - MBP maltose binding protein - mAb monoclonal antibody - WGA wheat germ agglutinin     

Antibodies from patients with drug-induced and idiopathic lupus erythematosus react with epitopes restricted to the amino and carboxyl termini of histone

The sera of patients with systemic lupus erythematosus (SLE) and drug-induced lupus (DIL) were used to study the antigenic epitopes on nuclear histones that bind antibodies in these sera. ELISA and immunoblotting techniques showed that antibodies from both patient groups bound all classes of intact histone: H1 greater than H2B greater than H2A greater than H3 greater than H4. The different classes of histone were enzymatically or chemically cleaved to produce a series of peptide fragments which were then used to map the reactive epitopes by ELISA and immunoblotting. Ten of 11 DIL sera and 11 of 12 SLE sera bound the carboxy and amino terminal peptides. Only one sera of each group bound to the central hydrophobic polypeptide. The reactivity of DIL sera with fractionated histone polypeptides was similar to that observed with SLE sera. This observation suggests that the histone epitopes reacting with DIL sera are no less restricted than those reacting with SLE.     

Systemic Lupus Erythematosus Patients Contain Significantly Less IgM against Mono-Methylated Lysine than Healthy Subjects

Post-translational modifications on proteins are important in biological processes but may create neo-epitopes that induce autoimmune responses. In this study, we measured the serum IgG and IgM response to a set of non-modified or acetyl- and methyl-modified peptides corresponding to residues 1–19 of the histone 3 N-terminal tail in systemic lupus erythematosus (SLE) patients and healthy subjects. Our results indicated that the SLE patients and healthy subjects produced antibodies (Abs) to the peptides, but the two groups had different Ab isotype and epitope preferences. Abs to the non-modified form, H3_1–19, were of the IgG isotype and produced by SLE patients. They could not recognize the scrambled H3_1–19, which contained the same amino acid composition but a different sequence as H3_1–19. In comparison, healthy subjects in general did not produce IgG against H3_1–19. However, about 70% of the healthy subjects produced IgM Abs against mono-methylated K9 of H3_1–19 (H3_1–19K9me). Our further studies revealed that ε-amine mono-methylated lysine could completely inhibit the IgM binding to H3_1–19K9me, but lysine had no inhibitory effect. In addition, the IgM Abs could bind peptides containing a mono-methylated lysine residue but with totally different sequences. Thus, mono-methylated lysine was the sole epitope for the IgM. Interestingly, SLE patients had much lower levels of this type of IgM. There was no obvious correlation between the IgM levels and disease activity and the decreased IgM was unlikely caused by medical treatments.We also found that the IgM Abs were not polyreactive to dsDNA, ssDNA, lipopolysaccharide (LPS) or insulin and they did not exist in umbilical cord serum, implying that they were not natural Abs. The IgM Abs against mono-methylated lysine are present in healthy subjects but are significantly lower in SLE patients, suggesting a distinct origin of production and special physiological functions.     

Autoantibodies to nucleolin in systemic lupus erythematosus and other diseases

The 110-kDa intracellular phosphoprotein (110K) described previously by this laboratory as a common IgM autoantigen in SLE and certain other systemic autoimmune disorders and viral infections is identified as nucleolin in the present investigation. Using rabbit antiserum to rat nucleolin as a probe, IgM autoantibody-reactive 110K co-migrated with human lymphocyte nucleolin in one- and two-dimensional immunoblots. Rabbit anti-nucleolin also specifically depleted autoreactive 110K from detergent lysates of human cells. Because nucleolin shares amino acid sequence similarity and/or forms dynamic particles with other prominent autoantigens, the present observation raises the possibility that the nucleolin/anti-nucleolin system may be of special significance for the development of humoral autoreactivity to nuclear Ag.     

Autoantibodies closely relate to the elevation level of in vivo hydrogen peroxide and tissue damage in systemic lupus erythematosus

Recent studies have shown that antibodies efficiently catalyze the conversion of molecular singlet oxygen (1O2) plus water to hydrogen peroxide (H2O2). H2O2 is toxic to cells and is a cause of further free radical generation that are implicated in the pathogenesis of a variety of diseases. Systemic lupus erythematosus (SLE) is one of the most serious autoimmune diseases which are characterized by the production of various autoantibodies and subsequent tissue damage. However, the correlation of autoantibodies, H2O2, and tissue lesion in SLE has not been yet investigated. To address this issue, in the present study, we induced autoantibodies and kidney tissue damage by using SLE animal model as described previously. We detected the level of H2O2 in SLE mice and found the increase of in vivo H2O2 was accompanied and closely correlated with the production of anti-dsDNA and antihistone antibodies. Importantly, there was onefold increase of H2O2 in the mice kidneys with apparent glomerulonephritis and IgG deposits. These results suggest that the induced autoantibodies possess catalytic activity. The produced autoantibodies lead to the production and elevation of H2O2, which results in subsequent renal damage and the pathogenesis of SLE. Our findings provide an insight into the understanding of SLE mechanism and provide a potential approach for therapeutic intervention of SLE.     

Ophiopogonin D attenuates the progression of murine systemic lupus erythematosus by reducing B cell numbers

Systemic lupus erythematosus (SLE) is a chronic autoimmune disease characterized by immune abnormalities leading to multi-organ damage. The activation of autoreactive B cell differentiation will lead to the production of pathogenic autoantibodies, contributing to the development of SLE. However, the effects of Ophiopogonin D (OP-D) on B cell activation and autoantibody production as well as renal injury in the pathogenesis of SLE remain unclear. MRL/lpr mice, one of the most commonly used animal models of SLE, were intragastrically administered with 5 mg/kg/d OP-D at 17 weeks of age for 3 weeks. The survival rates of mice in each group were monitored for 6 weeks until 23 weeks of age. Proteinuria and serum creatinine levels were measured. Serum levels of immunoglobulin (Ig)G, IgM, and anti-dsDNA autoantibodies were detected by enzyme-linked immunosorbent assay. Numbers of CD19⁺ B cells in the blood, spleen and bone marrow and numbers of splenic germinal center (GC) B cells were calculated by using flow cytometry. OP-D treatment prolonged survival in MRL/lpr mice. OP-D treatment reduced proteinuria and serum creatinine levels as well as mitigated renal pathological alternation in MRL/lpr mice. Furthermore, serum levels of IgG, IgM, and anti-dsDNA autoantibodies were reduced by OP-D treatment. OP-D lessened not only CD19⁺ B cells in the spleen and bone marrow but also plasma cells that secreted anti-dsDNA autoantibodies, IgG and IgM in the spleen and bone marrow. OP-D ameliorated the progression of SLE by inhibiting the secretion of autoantibodies though reducing B cell numbers.     

Internalization of anti-nucleolin antibody into viable HEp-2 cells

Anti-nucleolin antibodies have been detected in patients with systemic connective tissue diseases (SCTD) including systemic sclerosis (SSc) and systemic lupus erythematosus (SLE). In vivo bound autoantibodies to nucleoli of epidermal keratinocytes have been demonstrated in skin from patients with SCTD. In this study, monoclonal antibody to nucleolin (D-3) was used to determine the distribution of nucleolin in different culture cells including HEp-2, HepG2, HRCC, Molt-4 and Wil2 cells. Nucleolin was found to be present on the surface of HEp-2 and HepG2 cells, but not on the surface of HRCC and lymphoblastoid (Molt-4 and Wil2) cells; in contrast, nucleolin was detected in the nucleoli of all permeabilized cells examined. In immunoprecipitation, using extracts from ³²P-labeled HEp-2 cells as antigenic source, cell membrane as well as nuclear nucleolins were found to be phosphorylated with a molecular weight of 105 kDa. Viable HEp-2 and HepG2 cells were cocultured with IgG fraction of D-3 in a CO₂ incubator for 1 to 24 h, and then permeabilized with acetone followed by immunofluorescence staining with FITC-labeled goat anti-mouse IgG antibodies. Nucleolar staining was observed in cells after 10 h or longer of coculture. These data indicated that D-3 antibody reacted with cell membrane nucleolin and subsequently gain access into cells in a process related to pinocytosis.     

Natural autoantibodies to TCR public idiotopes: potential roles in immunomodulation.

Autoantibodies directed against variable domain epitopes of the alpha/beta T cell receptor (TCR) occur in sera of man, mouse and other vertebrates. Here, we focus upon autoantibodies expressed in human rheumatoid arthritis (RA) and systemic erythematosus (SLE) with parallel studies involving collagen induced arthritis (CIA) in mice transgenic for human HLA-DR conferring resistance or susceptibility to autoimmune disease. We report specificity characterization of polyclonal and monoclonal IgM and IgG autoantibodies from SLE and for IgM monoclonal autoantibodies of RA patients. The data suggests that autoantibodies directed against "public" idiotopes present in the first complementarity determining region (CDR1) and the third framework (FR3) of the Vbeta gene products are generated in response to over-production of autodestructive T cells bearing particular Vbeta gene products and function to modulate (downregulate) the expression of these T cells. Since antibodies of these specificities are present in polyclonal IgG immunoglobulin (IVIG) preparations used for therapeutic purposes, the immunomodulatory effects of antibodies directed against TCR variable domains may account, at least in part, for the efficacy of IVIG preparations in therapy of autoimmune diseases and in the prevention of graft versus host reactions.     

HDAC inhibition in lupus models

Systemic lupus erythematosus (SLE) is a prototypic autoimmune inflammatory disease characterized by the production of autoantibodies directed against nuclear antigens such as nucleosomes, DNA and histone proteins found within the body's cells and plasma. Autoantibodies may induce disease by forming immune complexes that lodge in target organs or by crossreacting with targeted antigens and damaging tissue. In addition to autoantibody production, apoptotic defects and impaired removal of apoptotic cells contribute to an overload of autoantigens that initiate an autoimmune response. Besides the well-recognized genetic susceptibility to SLE, environmental and epigenetic factors play a crucial role in disease pathogenesis as evidenced by monozygotic twins typically being discordant for disease. Changes in DNA methylation and histone acetylation alter gene expression and are thought to contribute to the epigenetic deregulation in disease. In SLE, global and gene-specific DNA methylation changes have been demonstrated to occur. Additionally, aberrant histone acetylation is evident in individuals with SLE. Moreover, histone deacetylase inhibitors (HDACi) have been shown to reverse the skewed expression of multiple genes involved in SLE. In this review, we discuss the implications of epigenetic alterations in the development and progression of SLE, and how therapeutics designed to alter histone acetylation status may constitute a promising avenue to target disease.     

Modulation of IgM anti-lymphocyte antibody-reactive T cell surface antigens in systemic lupus erythematosus

Cold-reactive lymphocytotoxic autoantibodies are present in the serum of most patients with active systemic lupus erythematosus (SLE) and may be important for the development of the lymphopenia and T cell dysfunction characteristic of this disorder. Neither the mechanisms of autoantibody action in this regard, nor the nature of the relevant T cell membrane target molecules have been defined, however. In the present investigation, preincubation of T cells with SLE serum at 37 degrees C reduced their reactivity with SLE IgM anti-lymphocyte autoantibodies, as demonstrated by indirect immunofluorescence and complement-dependent cytotoxicity. Modulation was restricted to SLE IgM autoantibody-reactive antigen; monoclonal antibody staining of various T cell differentiation and activation antigens remained unchanged. Loss of antigen from the surface membrane was rapid, but transient. A nadir was reached after approximately 120 min of 37 degrees C incubation, followed by essentially complete reexpression of antigen several hours later. Although modulation occurred spontaneously at 37 degrees C in the absence of SLE serum, loss of antigen was enhanced by IgM anti-lymphocyte autoantibodies, despite their low thermal amplitude. Modulation was inhibited by sodium azide, by fixation of cells with paraformaldehyde, and by low incubation temperatures. Colchicine and cytochalasin D had no effect on this process, suggesting that the integrity of the cytoskeleton was not essential. Cycloheximide did not prevent loss of antigen, but inhibited its reexpression. In experiments to determine the fate of modulated antigen, both intracytoplasmic accumulation and shedding from the cell surface were demonstrated. Only shedding was increased by the presence of anti-lymphocyte antibodies, however. These studies delineate modulation of T cell membrane antigen as a new mechanism for anti-lymphocyte autoantibody action in SLE. The occurrence of modulation at physiologic temperatures in vitro suggests that a similar phenomenon of potential relevance to T cell dysfunction may obtain in patients with this disorder.     

Interferon regulatory factor 1 and histone H4 acetylation in systemic lupus erythematosus

Histone acetylation modulates gene expression and has been described as increased in systemic lupus erythematosus (SLE). We investigated interferon regulatory factor 1 (IRF1) interactions that influence H4 acetylation (H4ac) in SLE. Intracellular flow cytometry for H4 acetylated lysine (K) 5, K8, K12, and K16 was performed. Histone acetylation was defined in monocytes and T cells from controls and SLE patients. RNA-Seq studies were performed on monocytes to look for an imbalance in histone acetyltransferases and histone deacetylase enzyme expression. Expression levels were validated using real-time quantitative RT-PCR. IRF1 induction of H4ac was evaluated using D54MG cells overexpressing IRF1. IRF1 protein interactions were studied using co-immunoprecipitation assays. IRF1-dependent recruitment of histone acetyltransferases to target genes was examined by ChIP assays using p300 antibody. Flow cytometry data showed significantly increased H4K5, H4K8, H4K12, and H4K16 acetylation in SLE monocytes. HDAC3 and HDAC11 gene expression were decreased in SLE monocytes. PCAF showed significantly higher gene expression in SLE than controls. IRF1-overexpressing D54MG cells were associated with significantly increased H4K5, H4K8, and H4K12 acetylation compared to vector-control D54MG cells both globally and at specific target genes. Co-immunoprecipitation studies using D54MG cells revealed IRF1 protein-protein interactions with PCAF, P300, CBP, GCN5, ATF2, and HDAC3. ChIP experiments demonstrated increased p300 recruitment to known IRF1 targets in D54MG cells overexpressing IRF1. In contrast, p300 binding to IRF1 targets decreased in D54MG cells with IRF1 knockdown. SLE appears to be associated with an imbalance in histone acetyltransferases and histone deacetylase enzymes favoring pathologic H4 acetylation. Furthermore, IRF1 directly interacts with chromatin modifying enzymes, supporting a model where recruitment to specific target genes is mediated in part by IRF1.     

A major nucleolar protein, nucleolin, induces chromatin decondensation by binding to histone H1

Using circular dichroism to probe the extent of DNA condensation in chromatin, we have demonstrated that a major nucleolar protein, nucleolin can decondense chromatin. By means of various binding assays we show that nucleolin has a strong affinity for histone H1 and that the phosphorylated N-terminal domain, rich in lengthy stretches of acidic amino acids, is responsible for this ionic interaction. Additional experiments clearly demonstrate that nucleolin is unable to act as a nucleosome core assembly or disassembly factor and hence has little affinity for the core histone octamer. We propose that this nucleolar protein induces chromatin decondensation by binding to histone H1, and that nucleolin can therefore be regarded as a protein of the high-mobility-group type.     

Pathogenic autoantibodies in systemic lupus erythematosus are derived from both self-reactive and non-self-reactive B cells

Previous studies have shown that both murine and human anti-double-stranded DNA (anti-dsDNA) antibodies can develop from non-DNA-reactive B cells and suggest a crucial role for somatic mutation in dsDNA binding. However, since only a limited number of human anti-dsDNA antibodies have been analyzed previously, we could not exclude other mechanisms for the generation of anti-dsDNA antibodies in patients with systemic lupus erythematosus (SLE). Therefore, we isolated IgM anti-dsDNA antibodies from peripheral blood B cells of a patient with SLE. Three somatically mutated IgM anti-DNA antibodies with pathogenic potential (glomerular binding) were reverted to their germline configuration. Although all three IgM anti-dsDNA antibodies came from the same lupus patient, they displayed different profiles. Reversion to the germline sequence of autoantibodies A9 and B5 resulted in decreased dsDNA binding. In contrast, the germline form of G3-recognized dsDNA as well as the mutated counterpart. These results suggest that mutated IgM anti-dsDNA antibodies may develop from both DNA- and non-DNA-reactive B cells. The implications are that B cell activation occurs in response to self and non-self antigens, while selection after activation may be mediated by self antigen in SLE. Moreover, ineffective tolerance checkpoints may exist before and after antigen activation in SLE.     

RFX1 regulates CD70 and CD11a expression in lupus T cells by recruiting the histone methyltransferase SUV39H1

Introduction  

Regulatory factor X-box 1 (RFX1) can interact with DNA methyltransferase 1 (DNMT1) and histone deacetylase 1 (HDAC1), and RFX1 down-regulation contributes to DNA hypomethylation and histone H3 hyperacetylation at the cluster of differentiation (CD) 11a and CD70 promoters in CD4⁺ T cells of patients with systemic lupus erythematosus (SLE). This leads to CD11a and CD70 overexpression, thereby triggering autoimmune responses. In order to provide more insight into the epigenetic mechanisms leading to the deregulation of autoimmune-related genes in SLE, we asked whether RFX1 is involved in regulating histone 3 lysine 9 (H3K9) tri-methylation at the CD11a and CD70 promoters in SLE CD4⁺ T cells.     

The epigenetic face of systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is an archetypical systemic, autoimmune inflammatory disease characterized by the production of autoantibodies to multiple nuclear Ags. Apoptotic defects and impaired removal of apoptotic cells contribute to an overload of autoantigens that become available to initiate an autoimmune response. Besides the well-recognized genetic susceptibility to SLE, epigenetic factors are important in the onset of the disease, as even monozygotic twins are usually discordant for the disease. Changes in DNA methylation and histone modifications, the major epigenetic marks, are a hallmark in genes that undergo epigenetic deregulation in disease. In SLE, global and gene-specific DNA methylation changes have been demonstrated to occur. Moreover, histone deacetylase inhibitors reverse the skewed expression of multiple genes involved in SLE. In the present study, we discuss the implications of epigenetic alterations in the development and progression of SLE and how epigenetic drugs constitute a promising source of therapy to treat this disease.     

Anti‐histone H1 IgGs from blood serum of systemic lupus erythematosus patients are capable of hydrolyzing histone H1 and myelin basic protein

Novel hydrolytic activity of the anti‐histone H1 antibodies (Ab) toward histone H1 and myelin basic protein (MBP) was shown. Blood serum of ten patients with clinically diagnosed systemic lupus erythematosus (SLE), and nine healthy donors (control) were screened for the anti‐histone H1 antibody‐ and anti‐MBP antibody‐mediated specific proteolytic activity. IgGs were isolated by chromatography on Protein G‐Sepharose, and four of ten SLE patients appeared to possess IgGs that were capable of cleaving both histone H1 and MBP. Such activity was confirmed to be an intrinsic property of the IgG molecule, since it was preserved at gel filtration at alkaline and acidic pH. At the same time, proteolytic activity was absent in the sera‐derived Ab of all healthy donors under control. Anti‐histone IgGs were purified by the affinity chromatography on histone H1‐Sepharose. Their cross‐reactivity toward cationic proteins (histones, lysozyme, and MBP) and their capability of hydrolyzing histone H1 and MBP were detected. However, these IgGs were not cleaving core histones, lysozyme, or albumin. Capability of cleaving histone H1 and MBP was preserved after additional purification of anti‐histone H1 IgGs by the HPLC gel filtration. The protease activity of anti‐histone H1 IgG Ab was inhibited by serine protease inhibitors. Copyright © 2010 John Wiley & Sons, Ltd.