Antibodies to histones in systemic lupus erythematosus: localization of prominent autoantigens on histones H1 and H2B.

Abstract

By the technique of immunoblotting we have assessed the ability of sera from 24 patients with systemic lupus erythematosus to bind nuclear proteins. Of the 11 patients who had antibodies to histones, 10 had antibodies to histone HI and 9 of these also had antibodies to histone H2B. Antibodies to the other histones (H2A, H3, and H4) were less apparent. Five of the 11 patients (and two others in the remainder of the sample of 24) also had antibodies to a small number of nonhistone proteins that are probably components of ribonucleoprotein particles, but there was no obvious correlation between the presence of antihistone antibodies and the known antiribonucleoprotein activity of these sera.Separate determinants on HI and H2B were demonstrated by immunoblotting with affinity-purified anti-HI and anti-H2B antibodies derived from serum that showed both specificities. The localization of the determinants within the histone polypeptide chains was shown by immunoblotting with large fragments produced by specific proteolytic or chemical cleavage of the histones. The strongest determinant on HI was located within the COOH-terminal half, with a weaker determinant being present within the NH2-terminal half; the H2B determinant(s) was located entirely within the NH2-terminal half of the molecule. The selectivity with which the antihistone antibodies in systemic lupus erythematosus are produced against the more exposed histones in the nucleosome (and perhaps against the most exposed regions of these histones) is consistent with the involvement of intact chromatin structures as immunogens in this disease.Antinuclear antibodies (ANAs) can be classified conveniently into groups directed against (i) ribonucleoproteins (RNP), (ii) deoxyribonucleoprotein, (iii) naked nucleic acids, and (iv) other constituents of the nucleus such as the nuclear matrix or enzymes. Recently, it has become clear that patients with systemic lupus erythematosus (SLE) produce at least nine different autoantibodies that recognize selected sets of RNP (1-3). Specificity within this system is based on the ability of the antibodies to identify proteins that bind with great selectivity to particular RNA molecules. These studies suggested that antibodies to deoxyribonucleoprotein might follow a similar pattern and represent a broad spectrum of specificities for different proteins that complex with DNA. In the present study, we have used the immunoblotting technique (4) to analyze the ability of antibodies in SLE sera to recognize nuclear protein antigens. The results indicate that the most prominent antigenic determinants of chromatin are located on histones, particularly HI and H2B, within regions that are likely to be exposed in the structure of native chromatin. MATERIALS AND METHODSPatients. We have studied 24 patients who fulfilled the American Rheumatism Association criteria for SLE (5). All had ANAs demonstrable by indirect immunofluorescence. The sera were stored at -70'C until assayed and transported from New Haven to Cambridge, England, in so...

Identification of New Pathogenic Players in Lupus: Autoantibody-Secreting Cells Are Present in Nephritic Kidneys of (NZBxNZW)F1 Mice

“…Using the two large cleavage H2B fragments 1-59 and 63-125 and sera from lupus patients, Hardin and Thomas also drew the same conclusion (22). Interestingly in this context, it has also been shown that the N-terminal region of H2B is readily exposed at the surface of mono-and polynucleosomes (29,38,39).…”

“…H2B is effectively targeted by lupus autoantibodies, and mAbs were generated from unprimed lupus mice with a higher prevalence compared with the other core histones (22)(23)(24). It contains a number of potential sites for posttranslational modifications, including apoptosis-specific ones (1).…”

Self antigens and epitope spreading in systemic autoimmunity

“…68), they are not known to bind, or be presented by APC, either DNA or RNA. Autoreactive B cells with Ig directed against DNA or against surface-exposed regions of histones (69,70) in nucleosomes can bind, internalize, and process the latter complexes in endosomallysosomal pathways, with presentation of histone peptides, by class IT MHC heterodimers, to autoreactive T cells derived from lupus-prone SNF, mice (23,24) as well as from SLE patients (28) (Figure 2). In the setting of appropriate costimulatory molecules and cytokines, the latter cells now provide help for anti-DNA production, as well as help for antihistone and antinucleosome antibodies; i.e., epitope spreading occurs among B cells, with resultant linkage of these antibodies with anti-DNA.…”

Protein L-Isoaspartyl Methyltransferase Catalyzes in Vivo Racemization of Aspartate-25 in Mammalian Histone H2B

“…It will be of interest to determine whether the D-Asp 25 form of H2B is differentially distributed between open and condensed regions of chromatin and whether it is relatively enriched or depleted in nucleosomes associated with active or repressed genes. Coincidentally, histone H2B is a major target of autoimmune responses in systemic lupus erythematosus (26). The formation of L-isoaspartyl sites, as well as other types of posttranslational modification of self-proteins, are believed to be key factors in eliciting autoimmunity in a number of diseases (27,28).…”