Characterization of a monoclonal antibody reacting with histone H3

Optimization of ligand presentation for immunoadsorption using star-configured polyethylene glycols

Medical, pharmaceutical, and industrial applications of immunoadsorption are frequently limited by the technologic problems of low affinity, inadequate capacity, hydrophobicity, and bioincompatibility. To overcome these difficulties we studied the use of star-burst configured polyethylene glycols (star-PEGs) with immunoreactive molecules covalently bound to the end of each of the multiple flexible arms. The optimum pH ranges were determined to maintain stability of the tresyl chloride modified star reagents, and the chemistry was designed for their subsequent linkage to the immunoadsorbent moiety. We then devised the chemical reactions using nitration or hydrazine activation to tether these 64-arm structures to polymer supports made of polysulfone or polymethylmethacrylate, respectively. Transmission, scanning, and atomic force microscopy confirmed the preservation of the star configuration, even after linkage to the luminal surface of hollow fiber devices. To establish that these modified devices also maintained immunoadsorption reactivity, we used a model having relevance for human autoimmune disease and demonstrated the clearance of antihistone antibodies by tethered histones. This novel approach to increasing the capacity of immunoadsorption benefits from the star configuration which provides a high density of ligand, improved hydrophilicity of the surface, spacing of reactive molecules away from the support structure, and possible optimization of epitope immunoreactivity by arm-to-arm interaction of the bound molecules.

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.

Antisera directed against anti-histone H4 antibodies recognize linker histones. Novel immunological probes to detect histone interactions

We introduce a novel immunological approach to detect structural interactions between chromosomal proteins. Antigenically pure core histone H4 was prepared from chicken erythrocytes and used to produce anti-histone H4 antisera. IgG fractions were isolated from purified anti-H4 antibodies and used as antigens to produce "second generation" antisera. Epitopes cross-reacting with the second generation antisera were then identified within chromosomal proteins. These epitopes were presumed to mimic the complementary molecular surface of the original anti-H4 antibodies, and thus proteins containing these epitopes were putatively identified as specific ligands of H4 in chromatin. Surprisingly, we found this immunoreactivity was predominantly directed against H1 compared with H5 from chicken erythrocytes. Further, the immunoreactive epitopes were located within the C-terminal tail domain of the linker histones. These results suggest similar complementary interactions occur between H4 and the C-terminal tail domain of H1s in native chromatin. This could occur either within a single nucleosome as suggested by a previous report (Banères, J.-L., Essalouh, L., Jariel-Encontre, I., Mesnier, D., Garrod, S., and Parello, J. (1994) J. Mol. Biol., 243, 48-59) or between neighboring nucleosomes within the condensed chromatin fiber. The implications of these results with regard to the structure of the chromatin fiber and the future utility of this technique are discussed.

Eukaryotic cell components that bind to chlamydial elementary bodies: the histones

HeLa-cell-membrane fractions isolated by sonication as used previously to identify chlamydial adhesins were examined by a blotting technique for binding chlamydial elementary bodies (EB). One HeLa cell protein with apparent molecular mass of 32 kDa was found to bind native EB. A monoclonal antibody (mAb) raised against this chlamydial binding host-cell protein reacted with eucaryotic histones. Histone fractions were capable of binding EB in an ELISA assay and histone H1 was identified as the chlamydial-binding host cell protein in the Hela cell membrane fraction. Probing with specific mAbs against histone H3 and DNA confirmed that chromatin components were present in the host-cell membrane extract. These data suggest that the HeLa-cell-binding chlamydial proteins were previously identified by their reaction with chromatin and not with membrane components.

Immunogenicity of free histones and of histones complexed with RNA

Histone antibodies have been obtained by immunizing rabbits with histones H1, H2A, H2B, H3, H4 and triacetylated H4, uncomplexed to RNA. The reactivity of these antibodies was investigated by ELISA using as antigen isolated histones and chromatin as well as thirty-five different synthetic peptides covering the entire sequence of the four core histones, two peptides of H1 and two acetylated peptides of H4. The binding of these antibodies to histones was also measured in immunoblotting and in microcomplement fixation (MCF) tests. In parallel experiments using the same assays the various antigens were tested with antisera raised against histones complexed with RNA. Antibodies induced in the absence of RNA did not react with histones in MCF tests nor with chromatin in ELISA but reacted with the histones in ELISA, although the antibody titers were somewhat lower than in the case of antisera to histone-RNA complexes. Antibodies to RNA-histone complexes reacted with histones in both ELISA and MCF tests. When they were tested with peptide-coated microtiter plates in a direct binding ELISA format, antibodies induced with uncomplexed histones recognized very few fragments which were mainly located in the N- and C-terminal ends of the histones.

Accessibility and structural role of histone domains in chromatin. biophysical and immunochemical studies of progressive digestion with immobilized proteases

The accessibility and role of histone regions in chromatin fibres were investigated using limited proteolysis with enzymes covalently bound to collagen membranes. The changes in chromatin conformation and condensation monitored by various biophysical methods, were correlated to the degradation of the histone proteins revealed by antibodies specific for histones and histone peptides. Upon digestion with trypsin and subtilisin, chromatin undergoes successive structural transitions. The cleavage of the C-terminal domains of H1, H2A and H2B, and of the N-terminal tail of H3 led to a decondensation of chromatin fibres, indicated by increases in electric birefringence and orientational relaxation times. It corresponds to a 15% increase in linear dimensions. The degradation of the other terminal regions of histones H3, H2A and H2B resulted in the appearance of hinge points between nucleosomes without alteration of the overall orientation of polynucleosome chains. Despite the loss of all the basic domains of H1, H3, H2A and H2B, no significant change in DNA-protein interactions occurred, suggesting that most of these protease-accessible regions interact weakly, if at all, with DNA in chromatin. Further proteolysis led to H4 degradation and other additional cleavages of H1, H2B and H3. This caused the relaxation of no more than 8% of the total DNA but resulted in changes in the ability of chromatin to condense at high ionic strength. More extensive digestion resulted in a total unravelling of nucleosomal chains which acquired properties similar to those of H1-depleted chromatin, although the globular part of H1 was still present. The data suggest that histone-histone interactions between H1 and core histone domains play a central role in stabilizing the chromatin fibres, and cuts in H3, H2A and H2B as well as H1, seem necessary for chromatin expansion. On the contrary, H4 might be involved in the stabilization of nucleosomes only.

Protamine-histone replacement and DNA replication in the male mouse pronucleus

The protamine to histone replacement in fertilized mouse eggs was studied by using antibodies to these proteins. Its course was followed with respect to DNA replication by autoradiography of 3H-thymidine-labeled fertilized eggs. It was found that protamines were replaced by histones before the onset of DNA replication.

Accessibility of an epitope common to all histone H3 variants in folded and unfolded chromatin as studied by a monoclonal antibody

In a recent publication the isolation and some characteristics of an anti-histone 3 monoclonal antibody, 1GB3 were described (Muller et al. FEBS Lett. 182: 459-464, 1985). We now report that the epitope recognized is phylogenetically conserved and located in the N-terminal part of H3, most likely between residues 40 and 50. Using the ELISA technique we found this region to be accessible in chromatin to the monoclonal antibody. The effect of non-ionic detergents on the adsorbtion of chromatin on microtiter plates was studied in this context. Immunological analysis of the reaction of the monoclonal antibody with chromatin by immunoinhibition and immunosedimentation shows that the H3 epitope is accessible in both folded and unfolded chromatin fibre as well as in high- and low-molecular weight oligonucleosomes.

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

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

Monoclonal autoantibodies recognizing histone variants

Balb/c mice were immunized with affinity purified Ro(SS-A) from human origin in order to allow the preparation of monoclonal anti-Ro(SS-A) antibodies. After fusion of mouse myeloma cells (line Sp2/0 A914) with spleen cells from one of these mice, anti-Ro(SS-A) monoclonals were not obtained, but, instead, two IgM producing hybridomas reactive with histone H1 and one with histone H2B. The specificity of the anti-H1 monoclonals was investigated by means of immunoblotting of very lysine-rich histone variants from mouse which were separated by two-dimensional gelelectrophoresis. One of them (CLB-ANA 105) has H1(0) specificity with respect to the histone variants of mouse and man, but recognizes H5 as well as H1 from Xenopus laevis. Another monoclonal (CLB-ANA 108) reacts with the variant H1c from mouse, exclusively. From the way these monoclonals were produced, we postulate that they were not the result of immunization, but comprise specificities of naturally occurring autoantibodies.

Immunological relationships among vertebrate lysine-rich histones

1. The relationship between sequence homology and immunological cross-reaction was investigated by enzyme-linked immunosorbent assay and immunoblotting using polyclonal antisera against lysine-rich histones (LRH) of known sequence, chicken H1 and H5, trout Hl and Xenopus H1s. 2. The order of immunological relatedness was consistent with known homologies among these LRH and goose H5, but quantitative correlations reflected varied locations of antigenic determinants. 3. When immunoblotting was extended to LRH from eight more vertebrates, it was evident that avian H5, mammalian H1o and anuran H1s form a sub-class, to which turtle H1s may belong, that urodele erythrocytes contain no H5-like histone and that fish "H5" is more like H1 than the H5/H1s/H1o subclass.

Evidence for absence of histones in the Crithidia luciliae kinetoplast: a study with anti-H2A and monoclonal anti-H3 antibodies

Recently, the specificity of the Crithidia luciliae immunofluorescent assay for the detection of antibodies to double-stranded deoxyribonucleic acid (dsDNA) has been questioned. It has been proposed that the kinetoplast of this trypanosome-like organism contains antigenic determinants other than dsDNA, presumably histones. Using anti-H2A and monoclonal anti-H3 antihistone antibodies, we have proved that there are no histones present in the Crithidia luciliae kinetoplast. False-positive results from the assay may be due to binding of antibodies to unidentified kinetoplast acid-extractable antigens other than histones.

Specificity of antibodies raised against triacetylated histone H4

Ten monoclonal antibodies (mAbs) were obtained by immunizing animals with triacetylated histone H4 from cuttle-fish. The fine specificity of these antibodies was studied using various populations of acetylated H4, (H3H4)2 tetramers and histone octamers as well as with acetylated and nonacetylated peptides of H4. None of these mAbs were found to recognize triacetylated H4. Only five of them bound to diacetylated, monoacetylated and nonacetylated H4. One antibody was specific for H4 associated in the form of histone octamers and did not bind to any nonacetylated or acetylated form of H4 monomers. Eight of the antibodies were specific for residues situated in the region 9-23 of H4. None of the mAbs was completely specific for acetylated forms of H4. In contrast, antisera raised in rabbits against triacetylated H4 reacted strongly with tri and diacetylated H4, weakly with monoacetylated H4 and barely or not at all with nonacetylated H4.

In vitro B-lymphocyte antigen priming against both non-immunogenic and immunogenic molecules requiring low amounts of antigen and applicable in hybridoma technology

A method to efficiently antigen-prime B-lymphocytes with low amounts (less than 1 microgram/10(8) cells) of either immunogenic or non-immunogenic molecules is described. Keyhole limpet hemocyanin (KLH) and histone were used as prototypes for strongly immunogenic and for phylogenetically conserved non-immunogenic epitopes, respectively. Several modifications of previously reported methods were applied to the system and resulted in the requirement of antigen amounts sufficiently low to be obtainable by elution of proteins from electrophoretic gels. Antigen priming against highly purified antigen preparations is thereby feasible even when purified material cannot be obtained by conventional biochemical procedures. The amount of T- and B-lymphocytes and interleukin-2 production was estimated under various conditions during the priming procedure, and those optimal for generation of a high number of antigen-specific B-lymphocytes determined. In vitro antigen-primed B-lymphocytes were immortalized by conventional hybridoma technology. By fusion of lymphoid cells with myeloma cells at each day during the antigen-priming period, the optimal day of fusion to generate antigen-specific hybridomas was determined. Further, in 12 experiments with different antigens, 11 monoclonal antibodies to histones H3 and H4, two to the murine glucose transporter, 17 to trinitrophenyl-sheep red blood cells, and 20 to KLH were obtained. All specific hybridomas produced IgMs, as the antigen-priming period could not be extended for more than 9-10 days, whereafter a rapid decay in B-lymphocytes occurred.