Receptor revision and systemic lupus

Studies over the past 10 years have shown that B cells can undergo secondary heavy- or light-chain immunoglobulin (Ig) rearrangements at various stages of their normal development, a process termed receptor editing. In the bone marrow, this mechanism is important to maintain tolerance because it can extinguish a self-reactive specificity without having to physically eliminate a potentially autoreactive B cell. In the periphery, secondary rearrangements may also play a role in the diversification and maturation of an immune response, although conclusive evidence for this process is still required. Individuals with systemic autoimmune diseases, such as lupus, show evidence of intricate abnormalities in receptor editing. On the one hand, decreased editing may not eliminate the self-reactive specificities that emerge during B-cell development in the bone marrow. Conversely, excessive secondary rearrangements, especially in the periphery where tolerance mechanisms are less effective, can result in the production of autoantibodies by edited B cells. It will be important to assess whether the complex editing defects observed during lupus are a primary susceptibility factor to this disease or if they are secondary to other abnormalities of lymphocyte development in these autoimmune patients.

B7-1 and B7-2 co-stimulatory molecules are required for mercury-induced autoimmunity

B7-1 (CD80) and B7-2 (CD86) molecules on antigen presenting cells play important roles in providing co-stimulatory signals required for activation and expansion of autoreactive T cells. Moreover, some reports have suggested that these molecules may have distinct functions in the differentiation of Th1 and Th2 cells. Mercury-induced autoimmunity in H-2s mice is characterized by lymphoproliferation of T and B cells, serum increases in IgG1 and IgE and production of antinucleolar antibodies (ANoA). The mechanisms responsible for the various manifestations of this syndrome have yet to be elucidated. To examine the contributions of B7 co-stimulatory molecules to this model, susceptible mice were treated with antibodies to B7-1, B7-2, or both during the development of mercury-induced autoimmunity. The combination of anti-B7-1 and anti-B7-2 antibodies prevented Hg-induced disease in H-2s mice. Additionally, single anti-B7-1 antibody treatment was sufficient to prevent Hg-induced ANoA production, but not IgG1 and IgE hypergammaglobulinaemia. Further, single antibody treatment with anti-B7-2 resulted in a partial reduction of ANoA titres but had no significant effect on total serum IgG1 and IgE levels. Taken together, these results indicate that B7-1 and B7-2 molecules are critical for the development of Hg-induced autoimmunity and suggest that the different manifestations of the syndrome are regulated by independent mechanisms.

Mercury enhances susceptibility to murine leishmaniasis

The genetic background of mice infected with Leishmania major determines the response to infection, resulting in a resistant or susceptible phenotype. Susceptible mice develop a T-helper type 2 (Th2)-type immune response following infection distinguished by the development of interleukin (IL)-4 secreting T cells in the lymph node and spleen. In SJL mice, which normally heal L. major lesions, subtoxic doses of mercury induce an autoimmune syndrome characterized by an expansion of Th2 cells. In this study, we examined the effect of mercury administration on the outcome of L. major infection in SJL mice. We show that subtoxic doses of mercuric chloride (HgCl2) exacerbate disease outcome in SJL mice resulting in increased footpad swelling and increased parasite burdens. Furthermore, the effects of HgCl2 treatment on resistance to L. major are time-dependent. The nonhealing phenotype was observed only if mice had been treated with HgCl2 prior to L. major infection for at least 1 week, a timepoint at which mice treated with HgCl2 alone had increased splenocyte IL-4 production. HgCl2 treatment also increased production of serum immunoglobulin (Ig)E and IgG1, two IL-4 dependent isotypes. These results show that HgCl2 treatment enhances the susceptibility to L. major in SJL mice, consistent with the induction of host Th2 parameters. These findings have implications for the role of mercury contamination in areas of endemic leishmaniasis.

Reciprocal induction of IL-10 and IL-12 from macrophages by low-density lipoprotein and its oxidized forms

Atherosclerosis is a chronic inflammatory disease. Several lines of evidence indicate that altered or modified lipoproteins contribute to plaque formation and lesion progression in atherogenesis. In this study we examined if lipoproteins and their oxidized forms can exert an immunomodulatory effect, thereby potentially influencing atherogenesis. We demonstrate that LDL, upon binding to its receptor, induces interleukin (IL)-10 production from macrophages and biases naive T cells to become Th2-like. In contrast, oxLDL induces IL-12 from macrophages and accordingly favors differentiation of naive T cells along a Th1 pathway. IL-10 is a potent anti-inflammatory cytokine with a number of potential effects that could dampen inflammation at sites of vascular wall damage, including downregulation of MHC and adhesion molecules and biasing of adaptive immune responses toward the anti-inflammatory, humoral immune-promoting Th2 T cell subset. These studies assign a new immunomodulatory role to LDLs and offer a potential means to upregulate IL-10 production and prevent arterial inflammation.

Ig heavy-chain gene revision: leaping towards autoimmunity

B cells can revise their antigen receptors outside the confines of the bone marrow by secondary Ig gene rearrangements. Although the initial motivation to perform these revisions might be to silence a self-reactive specificity, those B cells that reinitiate the recombination process can perform a series of "leaping" rearrangements and inadvertently shift their receptor specificity towards autoimmunity. Heavy-chain receptor revision, coupled with other atypical rearrangements, might contribute to autoantibody production in systemic lupus erythematosus.

Lupus anti-DNA autoantibodies cross-react with a glomerular structural protein: a case for tissue injury by molecular mimicry

Anti-DNA autoantibodies are the hallmark of human and murine systemic lupus erythematosus (SLE), an autoimmune rheumatic disease of unknown etiology. Some of these antibodies are believed to be pathogenic for kidney tissue and to initiate immune glomerulonephritis. However, the mechanisms by which anti-DNA antibodies participate in tissue injury remain controversial. We have studied the in vivo pathogenicity of anti-DNA monoclonal antibodies in immune deficient mice, using a panel of murine B cell hybridomas. No consistent genetic or immunochemical differences were found between pathogenic and non-pathogenic anti-DNA antibodies. However, the two antibody populations differed in their cross-reaction with the acidic actin-binding protein, alpha-actinin, that is known to play a major role in the structural integrity of glomerular filtration components. These results suggest that kidney dysfunction in SLE may be facilitated by protein-nucleic acid antigenic mimicry.

Diverse roles for the third complementarity determining region of the heavy chain (H3) in the binding of immunoglobulin Fv fragments to DNA, nucleosomes and cardiolipin

Autoantibodies to DNA and chromatin employ junctional diversity and somatic mutations to generate or enhance antigen recognition. To define the role of diversity generating mechanisms in the etiology of autoantibodies to nuclear antigens, the heavy (H) chain of a murine autoantibody, 3H9, was used in its somatically mutated or germ-line form in conjunction with its own or with heterologous CDR3 (H3) domains. The resulting H chains were expressed together with the 3H9 light (L) chain as single-chain Fv (scFv) in Escherichia coli and assayed for binding to DNA, nucleosomes, or cardiolipin by enzyme-linked immunosorbent assay. All recombinant scFv exhibited nearly identical binding to cardiolipin. In contrast, the binding to nuclear antigens was drastically reduced by the reversion of mutations in 3H9 or the exchange of H3, such that only 3H9 itself bound strongly to single-stranded DNA, double-stranded DNA and nucleosomes. The results illustrate diverse interactions between a single combining site and different autoantigens. The analysis of these interactions suggests that the 3H9 VH domain, as encoded by the germ line, directs binding to cardiolipin, whereas structural determinants of H3, in concert with the remainder of the combining site, guide the maturation of antibody binding toward nuclear autoantigens.

Heavy chain revision in MRL mice: a potential mechanism for the development of autoreactive B cell precursors

Abs reactive to DNA and DNA/histone complexes are distinguished by the presence of positively charged amino acids, such as arginine, in the heavy chain complementarity-determining region 3. The presence of these amino acids partly results from atypical V(H)-D-J(H) rearrangements such as D-D fusions and D inversions. Previous results in our laboratory demonstrated that newborn autoimmune MRL/MpJ-+/+ mice undergo these unusual recombinations more frequently when compared with normal C3H/HeJ controls. In addition, the heavy chain junctions in newborn MRL mice demonstrated a preferred usage of V(H)-proximal D genes and distal J(H) genes suggestive of secondary gene rearrangements. In this study we explore the possibility that adult MRL B220(+)IgM(-) pre B cells, which have not yet undergone Ag selection, exhibit similar rearrangement patterns. Indeed, MRL pre-B cells possessed more atypical rearrangements (D-D fusions) than those of C3H/HeJ mice. However, the biased use of upstream D genes and downstream J(H) genes observed in the newborn MRL mice was not present in the pre-B cell library. These results suggest that the heavy chain rearrangement process persists later during B cell life in lupus-prone mice and lead us to propose a model of heavy chain receptor revision in the periphery of autoimmune mice.

Immune complexes present in the sera of autoimmune mice activate rheumatoid factor B cells

The fate of an autoreactive B cell is determined in part by the nature of the interaction of the B cell receptor with its autoantigen. In the lpr model of systemic autoimmunity, as well as in certain human diseases, autoreactive B cells expressing rheumatoid factor (RF) binding activity are prominent. A murine B cell transgenic model in which the B cell receptor is a RF that recognizes IgG2a of the j allotype (IgG2aj), but not the b allotype, was used in this study to investigate how the form of the autoantigen influences its ability to activate B cells. We found that sera from autoimmune mice, but not from nonautoimmune mice, were able to induce the proliferation of these RF+ B cells but did not stimulate B cells from RF- littermate controls. The stimulatory factor in serum was found to be IgG2aj, but the IgG2aj was stimulatory only when in the form of immune complexes. Monomeric IgG2aj failed to stimulate. Immune complexes containing lupus-associated nuclear and cytoplasmic autoantigens were particularly potent B cell activators in this system. Appropriate manipulation of such autoantibody/autoantigen complexes may eventually provide a means for therapeutic intervention in patients with certain systemic autoimmune disorders.

An immuno-electron microscopical analysis of transcribing multinucleosomal templates: what happens to the histones?

Immuno-electron microscopy was used to visualize the structure of reconstituted chromatin after in vitro transcription by purified T7 RNA polymerase. T7 RNA polymerase disrupts the nucleosomal structure in the transcribed region. This disruption is not influenced by the template, linear or supercoiled, and the presence or absence of nucleosomal positioning sequences in the transcribed region. In this study, we used monoclonal autoantibodies reacting with the nucleosome core particles and epitopes within several regions of the four different core histones. Some of the residues recognized by the autoantibodies are accessible on the surface of the nucleosomes and some are more internal and therefore less exposed at the surface. We show that the loss of the nucleosomal configuration during transcription is due to the loss of histone/DNA binding and that at least part of the histones are transferred to the nascent RNA chains. Consequently, after in vitro transcription by T7 RNA polymerase, the nucleosomal template does not conserve its original configuration, and no interaction of antigen/antibodies is observed anymore in the region that has been transcribed. Therefore, we conclude that in our in vitro transcription assay, nucleosomes are detached from the template, and not simply unfolded with histones remaining attached to the DNA.

Molecular and structural properties of three autoimmune IgG monoclonal antibodies to histone H2B

In systemic autoimmune diseases such as lupus the immune system produces autoantibodies to nuclear antigens including DNA and histone molecules. In the present study, we describe three monoclonal IgG antibodies that have been obtained from lupus-prone MRL/lpr mice. These three antibodies react with the amino terminus of histone H2B, a region of the molecule that is accessible in chromatin. Using a series of overlapping H2B synthetic peptides and structural analogues, we have mapped the different epitopes recognized by these antibodies. We have also sequenced the combining sites (variable regions) of the antibodies and modeled their interactions with the corresponding epitopes. Overall, the data suggest that the mechanisms of interaction with antigen are different for each of the three antibodies, even though they all react with the amino-terminal domain of the histone H2B molecule. The results also suggest that the binding between these antibodies and histone H2B is different from that between most antibodies and conventional protein antigens since the heavy chain complementarity-determining region 3 appears to play only a limited role in the three antibodies tested. The study of the interaction between self-antigens and spontaneously occurring autoantibodies may help us elucidate the mechanisms driving the expansion of self-reactive lymphocytes.

Cytokine regulation of a rodent model of mercuric chloride-induced autoimmunity

Experimental models of chemically induced autoimmunity have contributed to our understanding of the development of autoimmune diseases in humans. Heavy metals such as mercury induce a dramatic activation of the immune system and autoantibody production in genetically susceptible rats and mice. This autoimmune syndrome is dependent on T cells, which are important for B-cell activation and cytokine secretion. Several studies have focused on the roles of T-helper (Th)1 and Th2 cells and their respective cytokines in the pathogenesis of mercury-induced disease. This article reviews recent studies that have examined the patterns of cytokine gene expression and where investigators have manipulated the Th1 and Th2 responses that occur during mercury-induced autoimmunity. Finally, we will discuss some biochemical/molecular mechanisms by which heavy metals may induce cytokine gene expression.

Murine mercury-induced autoimmunity: a model of chemically related autoimmunity in humans

Human exposure to certain compounds or therapeutic drugs can result in the development of an autoimmune syndrome. Mercury (Hg) induced autoimmunity is one of the few animal models in which administration of a chemical induces a specific loss of tolerance to self-antigens. After receiving subtoxic doses of Hg or other heavy metals, susceptible mouse strains rapidly develop highly specific antibodies to nucleolar antigens. In addition, these animals display a general activation of the immune system, especially pronounced for the Th2 subset and a transient glomerulonephritis with immunoglobulin deposits. Like many human autoimmune diseases, this syndrome is associated with the expression of susceptible major histocompatibility complex (MHC) class II genes. In this article, we review the essential features of this model, and we discuss the putative mechanisms by which Hg creates such a severe immune dysfunction.

Atypical VH-D-JH rearrangements in newborn autoimmune MRL mice

Antinuclear Abs are the hallmark of the autoimmune disease systemic lupus erythematosus (SLE). The ability of self reactive autoantibodies to bind to DNA and nucleosomes is partly conferred by an increased number of arginine and asparagine residues in the heavy chain third complementarity determining region. This increased content of cationic residues is primarily the result of unusual VH-D-JH rearrangements, which include D-D fusions and D gene inversions. While self Ag-driven clonal expansion is a major contributor to the production of antinuclear Abs in lupus, we explore in this study the hypothesis that newly emerging B cells from autoimmune mice display more frequently these unusual VH-D-JH rearrangements. To this end, libraries of PCR-generated VH-D-JH junctions from MRL and C3H newborn livers were analyzed. When compared with the C3H controls, D and JH gene usage in MRL junctions suggests a greater frequency of secondary D-JH rearrangements in this strain. Furthermore, B cells from the autoimmune-prone MRL mice have significantly increased numbers of atypical VH-D-JH rearrangements (D-D fusions and D inversions). Therefore, B cells from MRL mice manifest intrinsic defects that could confer an increased propensity to produce unusual VH-D-JH rearrangements early in ontogeny.

Mercury-induced autoimmunity in the absence of IL-4

In susceptible H-2S mice, mercuric chloride (HgCl2) induces an autoimmune syndrome characterized by production of anti-nucleolar antibodies (ANoA) and increased serum levels of IgG1 and IgE antibodies. The increase in serum IgG1 and IgE, which are under IL-4 control, suggests a role for the Th2 subset in the induction of this syndrome. We have previously shown that administration of IL-12, a potent Th1-promoting cytokine, resulted in a dramatic reduction of the HgCl2-induced anti-nucleolar antibody titres and inhibited serum IgG1 increase. These results suggest that Th1 T cells can down-regulate ANoA, and support a role for the Th2 subset in ANoA production, possibly via IL-4. To examine the role of IL-4 in this syndrome, C57Bl/6 mice (H-2b) with a targeted deletion of the IL-4 gene were mated with A.SW mice (H-2S) to yield H-2S mice lacking IL-4. We then analysed ANoA and serum immunoglobulin levels in these mice after HgCl2 treatment. While mercury-treated IL-4(-/-) H-2S mice had virtually no detectable serum IgG1 or IgE, and very low levels of IgG1 ANoA, these mice had levels of IgG2a and IgG2b class ANoA comparable to mercury-treated IL-4+ H-2S mice, indicating that IL-4 is not required for the ANoA response in mercury-induced autoimmunity.

IL-12 down-regulates autoantibody production in mercury-induced autoimmunity

In genetically susceptible H-2s mice, subtoxic doses of mercuric chloride (HgCl2) induce a complex autoimmune syndrome characterized by the production of anti-nucleolar IgG Abs, lymphoproliferation, increased serum levels of IgG1 and IgE Abs, and renal Ig deposits. Mercury-induced autoimmunity in H-2s mice provides a useful model for chemically related autoimmunity in humans. The increase in serum IgG1 and IgE, which are under IL-4 control, suggests a role for the Th2 subset in this syndrome. The IL-12 cytokine induces T cell proliferation and IFN-gamma production and is necessary for differentiation of naive T cells into the Th1 subset. To gain an understanding of T cell control in this syndrome and, in particular, Th1/Th2 regulation, we assessed the effect of IL-12 administration in mercury-induced autoimmunity. Groups of A.SW mice (H-2s) received HgCl2 plus IL-12, HgCl2 alone, or IL-12 alone. IL-12 treatment resulted in a dramatic reduction of the anti-nucleolar Ab titers. IL-12 also inhibited the HgCl2-induced serum IgG1 increase, but, in contrast, did not significantly affect IgE induction in this model. This observation may be related to our unexpected finding that IL-12 further potentiated the HgCl2-triggered IL-4 induction in this model. The levels of renal Ig deposits were similar in mice receiving HgCl2 alone or HgCl2 plus IL-12. Our results indicate that IL-12 can down-regulate the autoimmune component of this experimental syndrome and that the various manifestations of mercury-induced autoimmunity are independently regulated.

Antigen specificity of anti-nuclear antibodies complexed to nucleosomes determines glomerular basement membrane binding in vivo

Monoclonal anti-nuclear antibodies which are complexed to nucleosomes are able to bind to the glomerular basement membrane (GBM) in vivo, whereas purified antibodies do not bind. The positively charged histone moieties in the nucleosome are-responsible for the binding to anionic determinants in the GBM. We tested the hypothesis that the specificity of the autoantibodies complexed to the nucleosome influences the glomerular binding of the antibody-nucleosome complex. We induced the formation of these immune complexes in vivo, by intraperitoneal inoculation of hybridomas producing monoclonal anti-nuclear antibodies (four anti-histone, three anti-double stranded (ds)DNA and three anti-nucleosome antibodies) into nude BALB/c mice. In ascites and plasma from the mice inoculated with these hybridomas, nucleosome/autoantibody complexes were detected in comparable amounts. Immunofluorescence of kidney sections revealed that about 60% of the mice inoculated with anti-nucleosome or anti-dsDNA hybridomas had immunoglobulin deposits in the GBM, whereas only 15% of the mice with anti-histone hybridomas showed these deposits (p < or = 0.04). In the Matrigel-ELISA (used as a GBM surrogate) ascites from anti-nucleosome or anti-DNA hybridomas displayed significantly higher titers (p < or = 0.002) than ascites from anti-histone hybridomas. In conclusion, nucleosome/immunoglobulin complexes comprising anti-nucleosome or anti-dsDNA auto-antibodies do bind more frequently to the GBM in vivo than nucleosome/immunoglobulin complexes containing anti-histone antibodies. It therefore appears that the specificity of the antibody bound to the nucleosome is a critical determinant for the nephritogenic potential of the nucleosome-autoantibody complex.

An ELISA for detection of apoptosis

We describe a simple and convenient enzyme-linked immunosorbent assay (ELISA) for the detection of apoptosis in tissue culture. An early event in apoptosis is DNA fragmentation followed by release of nucleosomes into the cytoplasm. Our sandwich assay uses a pair of monoclonal antibodies specific for two nucleosomal epitopes to capture and detect cytoplasmic nucleosomes onto the ELISA plate. Our assay is about 500 times more sensitive than the detection of apoptotic DNA ladder by agarose electrophoresis and is especially suited for the testing of large numbers of samples.

Nucleosomes and histones are present in glomerular deposits in human lupus nephritis

BACKGROUND

Recently we showed that antinuclear autoantibodies complexed to nucleosomes can bind to heparan sulphate (HS) in the glomerular basement membrane (GBM) via the histone part of the nucleosome. Histones have been identified in glomerular deposits in human and murine lupus nephritis. In addition, a decreased HS staining in the GBM was found, most probably due to masking by deposition of antibodies complexed to nucleosomes.

METHODS

In this study we first investigated whether histones or nucleosomes could be identified in glomerular deposits in human lupus nephritis, and secondly whether the presence of these nuclear components was correlated with absence of HS staining. Kidney biopsies of SLE patients (11 with diffuse proliferative glomerulonephritis (DPGN) and six with membranous glomerulonephritis (MGN)) and non-SLE glomerular diseases were stained for histones. DNA, nucleosomes, IgG and HS.

RESULTS

Using a polyclonal anti-H3 1 21 antiserum, histones were detected in all patients with DPGN and in two of six patients with SLE-MGN (P < 0.01). Using a monoclonal antihistone antibody, histones were stained in three patients with DPGN, but in none of the biopsies with MGN. Using nucleosome specific monoclonal antibodies, nucleosomes were detected in five patients with DPGN, in two patients with MGN, but in none of the biopsies with non-SLE glomerulonephritis. HS staining was nearly absent in DPGN, whereas staining was only moderately reduced in patients with MGN and controls (P = 0.001).

CONCLUSION

Using polyclonal and monoclonal antihistone antisera, histones were identified in all patients with DPGN and their presence was associated with a decrease of HS staining. Nucleosomes were identified in five of 11 patients with DPGN and in two of six patients with MGN. This is the first demonstration of nucleosomes in glomerular deposits in SLE nephritis.

Autoantibodies to nucleosomes and histone-DNA complexes

Individuals with systemic autoimmune diseases develop autoantibodies to nucleosome antigens. For many years, investigators have devoted much effort to precisely mapping epitopes on individual chromatin components. This approach, however, overlooks the existence of determinants that result from multimolecular interactions among nucleosome elements, such as DNA and histones. Anti-nucleosome antibodies can recognize a variety of complex epitopes and are especially prevalent in spontaneous and drug-induced lupus. Using numerous monoclonal anti-nucleosome antibodies obtained from autoimmune mice, we have further characterized these determinants and sequenced the variable region genes of these autoantibodies. I herein review these studies and their implications for the origin of antinuclear autoantibodies.

Induction of anti-polycation antibodies in H-2s mice by immunization with nuclear antigens

Following administration of certain chemicals (heavy metals or lupus-inducing drugs), H-2s mice produce autoantibodies reacting with various nuclear antigens such as fibrillarin in the nucleolus and histones in chromatin. In the present study, we have immunized A.SW (H-2s) mice and their congenic counterparts A.BY (H-2b) mice with bovine thymus nuclei in Freund's adjuvant. As was previously observed with lupus-prone mice, such active immunization did not elicit antinuclear antibodies in any of the experimental groups. Surprisingly, the A.SW immunized with nuclei in adjuvant developed high titers of IgG antibodies that reacted exclusively with synthetic polycations. We obtained several monoclonal IgG antibodies from these mice and verified that these polycation-reactive antibodies were not directed against a specific nuclear antigen. The genetic analysis of the monoclonal antibodies further confirmed their clonal diversity. The mechanisms leading to the appearance of antibodies reactive with highly basic molecules in A.SW mice may be related to their predisposition to produce autoantibodies to cationic nuclear antigens (fibrillarin, histones) during chemically-induced autoimmunity.

Specificity of monoclonal anti-nucleosome auto-antibodies derived from lupus mice

Recently, anti-nucleosome antibodies, which do not bind to DNA or to individual histones, have been identified in longitudinal studies in lupus mice. These anti-nucleosome antibodies occur early in spontaneous SLE and are formed prior to other anti-nuclear specificities. However, nucleosomal epitopes are yet to be fully characterized. We selected a panel of six monoclonal anti-nucleosome antibodies (mAbs) (#2, #32, #34, PL2-6, LG8-1 and LG10-1) derived from lupus mice. These mAbs were tested in ELISA on subnucleosome structures and on a panel of 53 histone peptides, covering the entire sequence of the five histones. Two mAbs reacted with one of these peptides, but the reactivity hardly exceeded the background reactivity. Based on the nucleosome and subnucleosome ELISA we identified different recognition patterns. Three mAbs showed the highest reactivity towards the intact nucleosome. For two of them (#32 and LG8-1) the nucleosomal epitope was primarily located on H2A-H2B/DNA, whereas for mAb #34 this primary epitope was located on H3/H4/DNA. Two mAbs (#2 and PL2-6) showed the highest reactivity with H2A-H2B/DNA and one mAb (LG10-1) recognized H3-H4/DNA. In the subnucleosome ELISA all but one (mAb #32) recognized more than one epitope, including DNA complexed to a variety of cationic molecules. Comparing these reactivities we identified for all mAbs one specific nucleosomal epitope, whereas reactivity with other subnucleosomes was comparable to the reactivity towards DNA complexed with cationic molecules. In inhibition experiments both in ELISA and in immunofluorescence it was found that only one of the mAbs (i.e. PL2-6), recognizing an epitope on H2A-H2B/DNA as primary epitope, could be inhibited by H2A-H2B/DNA in fluid phase. The two mAbs recognizing an epitope on H3-H4/DNA as primary epitope could be inhibited by H3-H4/DNA in fluid phase. From these analyses, we conclude first that for these nucleosome specific mAbs linear histone peptides are not very important. Second, that these mAbs all recognize different epitopes on both H2A/H2B-DNA and H3/H4-DNA and third that some solid phase H2A/H2B-DNA epitopes are not expressed on fluid phase H2A/H2B-DNA. Our findings suggest that in SLE the nucleosome can act as auto-antigen and that there is no immunodominant beta cell epitope within the nucleosome.

Monoclonal antibodies from NZW x BXSB F1 mice to beta2 glycoprotein I and cardiolipin. Species specificity and charge-dependent binding

NZW x BXSB F1 mice develop a systemic autoimmune syndrome with various lupus-like manifestations. Male animals develop a degenerative coronary disease with myocardial infarction, resulting in death before 6 mo of age. The presence in these mice of anti-phospholipid Abs reacting with beta2-glycoprotein I may contribute to the pathogenesis of the cardiovascular lesions. beta2-glycoprotein I, a plasma protein implicated in various aspects of the coagulation pathway, is also the target of autoantibodies in humans with the anti-phospholipid syndrome. We obtained several mAbs from NZW x BXSB F1 mice that were selected for binding to cardiolipin. Two mAbs are specific for beta2-glycoprotein I and display a species-dependent pattern with preferential reactivity to mouse beta2-glycoprotein I. The other mAbs display charge-mediated interactions with anionic phospholipids in the absence of beta2-glycoprotein I. The analysis of the V region sequences of the mAbs suggests that cationic residues in the H chain complementarity-determining region 3 are important for their phospholipid reactivity. The structural features of the V(H)-D-J(H) junctions of these mAbs further support the view that an increased frequency of unusual V(D)J rearrangements directly contributes to the development of murine autoimmunity.

Monoclonal antibodies from NZW x BXSB F1 mice to beta2 glycoprotein I and cardiolipin. Species specificity and charge-dependent binding

NZW x BXSB F1 mice develop a systemic autoimmune syndrome with various lupus-like manifestations. Male animals develop a degenerative coronary disease with myocardial infarction, resulting in death before 6 mo of age. The presence in these mice of anti-phospholipid Abs reacting with beta2-glycoprotein I may contribute to the pathogenesis of the cardiovascular lesions. beta2-glycoprotein I, a plasma protein implicated in various aspects of the coagulation pathway, is also the target of autoantibodies in humans with the anti-phospholipid syndrome. We obtained several mAbs from NZW x BXSB F1 mice that were selected for binding to cardiolipin. Two mAbs are specific for beta2-glycoprotein I and display a species-dependent pattern with preferential reactivity to mouse beta2-glycoprotein I. The other mAbs display charge-mediated interactions with anionic phospholipids in the absence of beta2-glycoprotein I. The analysis of the V region sequences of the mAbs suggests that cationic residues in the H chain complementarity-determining region 3 are important for their phospholipid reactivity. The structural features of the V(H)-D-J(H) junctions of these mAbs further support the view that an increased frequency of unusual V(D)J rearrangements directly contributes to the development of murine autoimmunity.

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.

Lack of temporal association of iridocyclitis with IgG reactivities to core histones and nucleosome subparticles in pauciarticular juvenile chronic arthritis

This study aimed to measure IgG reactivities to DNA-free nucleosome subparticles (H2AH2B, H3H4) and nucleosome subparticles (H2AH2B-DNA, H3H4-DNA) and to evaluate the temporal relation of these reactivities, as well as those to single core histones, with iridocyclitis (IC) in patients with antinuclear antibody positive (ANA+) pauciarticular juvenile chronic arthritis (JCA). Reactivities to nuclear substrates were determined by enzymatic immunoassays in 120 sera from 45 children with ANA+ pauciarticular JCA. Significantly elevated IgG levels to H3 and H4, to DNA-free nucleosome subparticles, and to the nucleosome subparticle H3H4-DNA were present in patients with ANA+ pauciarticular JCA; no evidence of recognition of conformational epitopes was found. In both horizontal and follow-up studies, no relation between the reactivities studied and the development, presence, or history of IC was found. Our results show the absence of a relation of antibodies to histone molecules or to nucleosome subparticles with IC in patients with ANA+ pauciarticular JCA.

Idiotypic diversity and variable region gene usage by mouse anti-HLA-DQ3 mAb

The anti-HLA-DQ3 monoclonal antibodies (mAb) KS13, SO1, SO2, SO3, SO4, and SO5 recognize spatially close but distinct antigenic determinants, since they crossinhibit each other in their binding to HLA-DQ3 antigens, but do not share idiotopes recognized in their antigen combining site by syngeneic and anti-id antisera and mAb. Furthermore, mAb SO1, SO3, SO4, and SO5 react also with HLA-DQ allospecificities other than HLA-DQ3. Sequence analysis of the heavy (VH) and light (VL) chain variable region of the six mAb revealed preferential usage of VH 36-60 and VK 12/13 gene families. However, the individual VH and VL germline gene usage by the six mAb is diverse and the utilization of D, JH, and JL gene segments is heterogeneous. The diverse usage of VH and VL gene segments and heterogeneous amino acid sequences of VH and VL CDR, together with the heterogeneous idiotypic profile, may reflect the complexity of the determinants recognized by the six mAb on HLA-DQ3 antigens. The results we have presented provide for the first time information about the structural basis of the diversity of antibodies recognizing human histocompatibility antigens.

Autoantibodies to histone, DNA and nucleosome antigens in canine systemic lupus erythematosus

Dogs can develop systemic lupus erythematosus syndromes that are clinically similar to those seen in humans. In contrast, previous observations suggest differences in their autoantibody reactivity patterns against histones and DNA which are components of the nucleosome in chromatin. The objective of this study was to assess comprehensively the levels of autoantibodies against histone, DNA and nucleosome antigens in a population of lupus dogs. The specificities of antibodies in lupus and control dog sera were determined using IgM- and IgG-specific reagents in an ELISA against a variety of chromatin antigens. When compared with control sera, IgG antibodies to individual histones H1, H2A, H3 and H4 were significantly higher in the lupus group. In contrast, we did not detect IgG antibodies specific for H2B, H2A-H2B, DNA, H2A-H2B-DNA or nucleosome in lupus dogs. There was no significant increase in any of the IgM specificities tested. Therefore, the reactivity pattern to nucleosome antigens in canine lupus is restricted to IgG antibodies against individual histones H1, H2A, H3 and H4. This stands in contrast with human and murine lupus, where autoantibodies are directed against a wide variety of nucleosomal determinants, suggesting that unique mechanisms lead to the expansion of anti-histone antibody clones in canine lupus. The high incidence of glomerulonephritis in dog lupus suggests that anti-DNA antibodies are not required for the development of this complication, whereas IgG anti-histone antibodies may be relevant to its pathogenesis.

Structural profile of idiotype, anti-idiotype and anti-anti-idiotype monoclonal antibodies in the HLA-DQ3 antigenic system

Interest in the characterization of idiotype cascades in the HLA antigenic system has been stimulated by their potential role in the immune response to mismatched HLA allospecificities and in the survival of kidney allografts. Since no information is available about the structural organization of idiotypic cascades in the HLA system, we have sequenced the variable regions of the heavy (VH) and light (VL) chains of mouse anti-HLA-DQ3 monoclonal antibody (mAb) KS13 elicited by cell membrane-bound antigens, of syngeneic anti-HLA-DQ3 mAb S2B154 elicited by anti-idiotypic (anti-id) mAb K03-34 and of five syngeneic anti-id mAb elicited by mAb KS13. mAb KS13 and S2B154, which have been previously shown to be very similar in their specificity and idiotypic profile, share several structural characteristics. Their VH and VL regions are encoded by the same VH, VK and JH genes, display relatively similar V(D)J rearrangements and differ only through a few amino acid substitutions. Among the five anti-id mAb elicited by mAb KS13, mAb R1-38 and R18-9 utilize multiple genetic elements that are different from those used by anti-id mAb KO3-34, K03-256 and K03-335. These results indicate that diverse V region combinations can confer an anti-id specificity in the antigenic system analyzed. mAb K03-34, K03-256 and K03-335 originate from the same B cell clone, since they use the same V, D and J genes and possess identical V(D)J rearrangements. The latter three anti-id mAb differ only by point mutations, which have dramatic effects on the HLA-DQ3 antigen mimicry properties of the three anti-id mAb. mAb K03-34 is the only one to induce anti-HLA-DQ3 antibodies both in syngeneic and xenogeneic hosts. The antigen mimicry properties of anti-id mAb K03-34 depend upon its three-dimensional conformation, since no significant amino acid sequence homology has been found between its VH and VL regions and alpha 1 and beta 1 domains of HLA-DQ3 antigens.

D-penicillamine- and quinidine-induced antinuclear antibodies in A.SW (H-2s) mice: similarities with autoantibodies in spontaneous and heavy metal-induced autoimmunity

Ten percent of human lupus syndromes occur in patients as a result of treatment with certain medications. H-2s mice can produce autoantibodies following treatment with various drugs or heavy metals and they are a potential animal model of drug-induced lupus. We have examined nine anti-chromatin monoclonal antibodies (mAb) from A.SW mice that had been treated with either D-penicillamine or quinidine, two lupus-inducing drugs in humans. These mAb are specific either for DNA or histone-DNA complexes corresponding to nucleo-specific either for DNA or histone-DNA complexes corresponding to nucleosomes or subnucleosome particles. Only one mAb reacts with an unknown chromatin antigen. The V region sequences of six of these mAb were studied and are notable by several features. As previously observed in spontaneous autoantibodies to DNA or histone-DNA complexes, arginine or asparagine residues are found at critical locations throughout the V regions. Many of these residues, potentially important for binding to DNA or DNA-histone complexes, result either from somatic mutations or atypical VH-D-JH rearrangements. Another significant characteristic is that the VH genes of several D-penicillamine- or quinidine-induced mAb are most similar to those of anti-nucleolar mAb obtained from mercury-injected A.SW mice. The implications of these findings for the pathogenesis of spontaneous or induced autoimmunity are discussed.

Anti-double stranded DNA, anti-histone, and anti-nucleosome IgG reactivities in children with systemic lupus erythematosus

In this study we evaluated the presence of anti-nucleosome reactivity in children with systemic lupus erythematosus (SLE), and assessed its clinical correlations in comparison with anti-dsDNA and anti-histone IgG levels. Reactivities to nuclear substrates were determined by enzymatic immunoassays in 80 sera from 22 children with SLE, and solid phase adsorption experiments were performed. In children with active SLE, the anti-dsDNA, anti-histone, and anti-nucleosome IgG levels were elevated, and were significantly correlated with disease severity; during remission anti-histone (but not anti-dsDNA and anti-nucleosome) antibodies, although reduced, were still significantly elevated. The results of adsorption studies showed that anti-dsDNA antibodies contributed to anti-nucleosome reactivity, while anti-histone antibodies did not. The recognition of the H3H4-DNA nucleosome subparticle, rather than H2AH2B-DNA, may be related to the nucleosome reactivity. In children with SLE anti-nucleosome reactivity is present; it is in part due to anti-dsDNA antibodies and in part to antibodies recognizing conformational epitopes that may be related to the H3H4-DNA nucleosome subparticle. Its clinical significance for diagnosis is not greater than that of the anti-dsDNA antibodies.

Mimicry of a carcinoembryonic antigen epitope by a rat monoclonal anti-idiotype antibody

Anti-idiotype antibodies (Ab2) that immunologically mimic tumor antigens are auspicious agents for the active immunization of cancer patients. We have developed W12, a rat monoclonal IgG1 Ab2 to MN-14, a murine anti-carcinoembryonic antigen (CEA) monoclonal antibody. W12 is specific for MN-14 and does not react with other isotype-matched anti-CEA monoclonal antibodies. Moreover, W12 inhibits the binding between MN-14 and CEA. Anti-CEA antibodies can be induced by immunization with W12 (but not with control rat IgG) in xenogenic animals (mice or rabbits). Immunoblotting studies indicate that the internal image determinant borne by W12 is conformational and requires the association of the heavy and light chains of the Ab2 molecule. This study indicates that W12 is a potential idiotype vaccine in patients with CEA-producing cancers.

Molecular analysis of mercury-induced antinucleolar antibodies in H-2S mice

In H-2S mice, the administration of mercuric chloride results in the development of antinucleolar autoantibodies. These mice represent a valuable model to study the role of environmental factors in the development of systemic autoimmunity. We have obtained seven antinucleolar mAb from mercury-injected A.SW mice and characterized their specificities and V genes. All mAb immunoprecipitate the U3 and U8 ribonucleoprotein particles (RNP) and some (but not all) react with fibrillarin, the only currently characterized protein component of mammalian nucleolar RNP. Several VH and V kappa genes are recurrently used by these antinucleolar RNP mAb and their H chain CDR3 segments contain several acidic residues that may be important for binding to the cationic proteins composing the nucleolar RNP. Our results support the concept that in H-2S mice administration of mercury induces a specific loss of tolerance to nucleolar RNP.

Molecular analysis of mercury-induced antinucleolar antibodies in H-2S mice

In H-2S mice, the administration of mercuric chloride results in the development of antinucleolar autoantibodies. These mice represent a valuable model to study the role of environmental factors in the development of systemic autoimmunity. We have obtained seven antinucleolar mAb from mercury-injected A.SW mice and characterized their specificities and V genes. All mAb immunoprecipitate the U3 and U8 ribonucleoprotein particles (RNP) and some (but not all) react with fibrillarin, the only currently characterized protein component of mammalian nucleolar RNP. Several VH and V kappa genes are recurrently used by these antinucleolar RNP mAb and their H chain CDR3 segments contain several acidic residues that may be important for binding to the cationic proteins composing the nucleolar RNP. Our results support the concept that in H-2S mice administration of mercury induces a specific loss of tolerance to nucleolar RNP.

Histone-reactive IgA antibodies in adult IgA nephropathy and other primary glomerulonephritis

The levels of histone-reactive IgA antibodies in the sera of adult patients with IgA mesangial glomerulonephritis, membranous glomerulonephritis, membranoproliferative glomerulonephritis and idiopathic nephrotic syndrome (minimal change disease+segmental glomerulosclerosis+IgM nephropathy) were evaluated by an enzyme-linked immunosorbent assay. Increased levels of IgA antibodies to all five major histones (H1, H2A, H2B, H3, H4) were found in all four disease groups when compared to normal controls. These histone-reactive IgA antibodies were restricted to the IgA1 subclass and their levels did not correlate with the levels of total serum IgA, nor with serum creatinine, creatinine clearance, and 24-hour proteinuria. Increasing ionic strength resulted in only partial inhibition of the binding to histones and, in individual patients, levels of reactivity with individual histones were usually correlated. This study shows that elevated levels of IgA antibodies reactive with self antigens are present in primary glomerulonephritis and extends previous observations indicating that anomalies of the IgA system occur in various forms of primary glomerulonephritis and are not limited to IgA nephropathy.

Structure and binding properties of monoclonal antibodies to core histones from autoimmune mice

Histones are frequent targets of self-reactive antibodies during autoimmune syndromes. We report the specificities and V region genes of three IgG anti-histone MAbs obtained from autoimmune mice. Each of the MAbs, named LG2-1, LG2-2 and BWA3, is directed against a different determinant located in the basic amino-terminal domain of core histones. LG2-1 reacts with a peptide from histone H3 (residues 30-45), LG2-2 recognizes the amino-terminus of H2B (residues 1-13) and BWA3 binds an epitope corresponding to a region of high sequence similarity between H2A and H4 (residues 1-20 and 1-29, respectively). The analysis of their V region sequences indicates that the H chain CDRs of these MAbs are remarkable for the presence of negatively charged amino acid residues that may play a role in the binding to cationic histones. The H chain importance in conferring reactivity to histones is corroborated by the observation that each of the VH gene segments of these MAbs is very similar to VH genes of previously described murine anti-histone antibodies.

Relationships among antinuclear antibodies from autoimmune MRL mice reacting with histone H2A-H2B dimers and DNA

The histone H2A-H2B dimer is a component of nucleosomes in chromatin and a frequent target of autoantibodies in spontaneous and drug-induced lupus. We obtained a panel of several lgG mAbs reacting with H2A-H2B or DNA from MRL mice which develop a spontaneous lupus-like syndrome. Several of these antibodies do not react with individual histones, but bind strongly to the H2A-H2B dimer and some bind even more strongly to the H2A-H2B-DNA complex. Moreover, these antibodies not only bind to H2A-H2B dimers in the absence of DNA, but also exhibit significant binding to DNA in the absence of histones, indicating an overlap between the anti-histone and anti-DNA specificities. The analysis of the variable region gene sequences of these antibodies shows a recurrent usage of similar VH genes, suggesting a dominant role for the heavy chain in determining binding specificity. The heavy chain third complementarity determining regions of these antibodies are also remarkable for their frequency of D-D fusions and of D segments read in unusual reading frames and for many arginine residues that may contribute to DNA binding. In addition, several antibodies obtained from an individual mouse are clonally related and some differ through somatic mutations, indicating that autoreactive clones are positively selected by nuclear antigens.

Nucleosome-specific antibody from an autoimmune MRL/Mp-lpr/lpr mouse

OBJECTIVE

To characterize the binding properties and variable-region sequences of LG4-1, a monoclonal antibody from an autoimmune MRL/Mp-lpr/lpr mouse that reacts specifically with nucleosome core particles and represents a new antinuclear antibody specificity.

METHODS

The reactivity of the antibody against various nuclear substrates was determined using an enzymatic immunoassay, and the variable-region genes were sequenced from messenger RNA, using the dideoxy chain termination method.

RESULTS

LG4-1 was found to react with nucleosome core particles but not with individual histones and DNA, or with various histone-histone and histone-DNA complexes. It was demonstrated that this antibody is encoded by a combination of variable-region genes and gene segments that have undergone few somatic mutations.

CONCLUSION

The nucleosome core particle expresses a unique conformational autoepitope(s) resulting from the ordered association of histones and DNA.

Polyreactive IgM antibodies generated from autoimmune mice and selected for histone-binding activity

A panel of histone-reactive IgM mAbs was obtained from mice belonging to various spontaneously autoimmune strains. Most of these antibodies were polyreactive, i.e. they showed binding to other cationic antigens (poly-L-lysine, lysozyme, cytochrome c) or to cytoskeletal proteins (actin, myosin, vimentin). The variable regions of these antibodies were encoded by V genes and gene segments belonging to various families. Their H chain third hypervariable regions were unusual in that the D segments were read in all three possible reading frames in contrast to most conventional antibodies and other polyreactive antibodies obtained from normal mice.

Enhanced clearance of radiolabeled murine monoclonal antibody by a syngeneic anti-idiotype antibody in tumor-bearing nude mice

A syngeneic anti-idiotype monoclonal antibody (MAb) (CM-11) directed against an anti-carcinoembryonic antigen (CEA) murine MAb (NP-4) was evaluated as a second antibody (SA) to promote the rapid clearance of radiolabeled NP-4 from the blood. Initial studies confirmed that CM-11 IgG removed 131I-NP-4 IgG from the blood as effectively as a polyclonal donkey anti-goat IgG removed 131I-goat IgG. However, use of an F(ab')2 in place of either the NP-4 or CM-11 IgG was not as effective in removing primary radiolabeled antibody, despite the formation of high-molecular-weight complexes. In accordance with previous results, the timing and dose of the SA injection was critical for optimizing tumor uptake and improving tumor/non-tumor ratios. In nude mice bearing GW-39 human colonic tumor xenografts, a delay in the injection of CM-11 by 48 hr after injection of radiolabeled NP-4 was optimal, since this allowed maximum tumor accretion. At a 200:1 CM-11:NP-4 ratio, tumor uptake was reduced, suggesting inhibition of NP-4 binding to CEA within the tumor. Despite optimizing tumor uptake by delaying SA injection and adjusting its dose, the percentage of 131I-NP-4 in the tumor decreased 2- to 3-fold within 2 days after CM-11 injection. A similar effect was seen for 111In-labeled NP-4 IgG with CM-11. Injection of excess unlabeled NP-4 given to block CM-11 shortly after its injection failed to curtail the loss of NP-4 from the tumor. Our results suggest that high blood levels of MAb are important for sustaining NP-4 in the tumor. Radiation-dose predictions derived from biodistribution studies indicate that a higher tumor dose may be delivered using the SA method than with either 131I-NP-4 IgG or F(ab')2 alone. Use of the SA method with 90Y-labeled NP-4 IgG, as modeled from biodistribution studies with 111In-NP-4 IgG, would likely be limited by liver toxicity.

Antibodies to histones in systemic lupus erythematosus and drug-induced lupus syndromes

Antihistone antibodies are some of the most frequent autoantibodies in rheumatic diseases and can represent useful diagnostic markers in some autoimmune syndromes. Histone epitopes are often located in accessible regions of chromatin or are conformational determinants resulting from the association of several components. These observations and studies with murine models of lupus strongly support the view that histones play a direct stimulatory role in triggering autoantibody production.

Monoclonal autoantibodies to subnucleosomes from a MRL/Mp(-)+/+ mouse. Oligoclonality of the antibody response and recognition of a determinant composed of histones H2A, H2B, and DNA

MRL/Mp(-)+/+ mice produce antinuclear antibodies and develop a spontaneous autoimmune syndrome with lupus-like nephritis. We obtained a panel of seven histone-reactive IgG mAb from a single MRL/Mp(-)+/+ mouse. These antibodies do not react significantly with DNA or individual histones, but bind strongly to the histone H2A-H2B dimer and even more strongly to the H2A-H2B-DNA complex. These antibodies also bind to whole nuclei when tested by immunofluorescence, indicating that they recognize an epitope accessible in chromatin. The V region sequences of these antibodies have been determined. The H chain third complementarity-determining regions of these antibodies are similar to those found in anti-DNA antibodies even though the antibodies in our panel do not react with DNA in the absence of histones, suggesting that DNA is part of the subnucleosome epitope. Several of these antibodies are clonally related, supporting the hypothesis that the activation of these clones is Ag-driven. Analysis of the sequences of these antibodies indicates that they derive from autoreactive B cells that were clonally expanded and whose V region genes have undergone numerous somatic mutations.

Monoclonal autoantibodies to subnucleosomes from a MRL/Mp(-)+/+ mouse. Oligoclonality of the antibody response and recognition of a determinant composed of histones H2A, H2B, and DNA

MRL/Mp(-)+/+ mice produce antinuclear antibodies and develop a spontaneous autoimmune syndrome with lupus-like nephritis. We obtained a panel of seven histone-reactive IgG mAb from a single MRL/Mp(-)+/+ mouse. These antibodies do not react significantly with DNA or individual histones, but bind strongly to the histone H2A-H2B dimer and even more strongly to the H2A-H2B-DNA complex. These antibodies also bind to whole nuclei when tested by immunofluorescence, indicating that they recognize an epitope accessible in chromatin. The V region sequences of these antibodies have been determined. The H chain third complementarity-determining regions of these antibodies are similar to those found in anti-DNA antibodies even though the antibodies in our panel do not react with DNA in the absence of histones, suggesting that DNA is part of the subnucleosome epitope. Several of these antibodies are clonally related, supporting the hypothesis that the activation of these clones is Ag-driven. Analysis of the sequences of these antibodies indicates that they derive from autoreactive B cells that were clonally expanded and whose V region genes have undergone numerous somatic mutations.

Epitope recognition in histone H1 by SLE autoantibodies in the presence of a DNA-ligand

To investigate the specificity of anti H1 antibodies peptides from the N- and C-domain of H1 and the synthetic oligonucleotide (AT)6 were complexed. Circular dichroism (CD) spectroscopy indicated that the free peptides H1(1-16), H1(204-218) and C(121-210) in low salt buffer assume a random structure but become helical when bound to the oligonucleotide. The structured and unstructured H1 fragments were then analyzed by enzyme linked immunosorbent assay (ELISA) with anti-H1 antibodies in sera from patients with systemic lupus erythematosis (SLE) and with the monoclonal anti-H1 antibody MRA-12 derived from MLR lpr/lpr autoimmune mice. Binding of these antibodies to H1(204-218) and C was inhibited to a level of 50% when these H1 peptides were complexed with (AT)6. When the same antibody was tested with H1 fragment GC(34-210), attachment to oligonucleotide (AT)6 did not influence antibody binding. Competition studies with liquid phase GC and C antigen against solid phase GC and C indicated that liquid phase GC was more efficient in displacing antibody binding reactivity than liquid phase C. The displacement effect of both liquid phase antigens was greatest against solid phase C. We conclude that anti-H1 autoantibodies are directed against an epitope located near the junction of the G- and C-domain which is exposed and not masked when H1 is bound to DNA.

Anti-histone antibodies in subacute sensory neuropathy

We investigated the levels of anti-histone antibodies in the sera of 7 patients with subacute sensory neuropathy. IgG antibodies to histones H1 and H3 were significantly elevated in 4 of these patients. The anti-H1 antibodies reacted mainly with determinants located in the central globular and the carboxy-terminal domain of the H1 molecule. We also observed reactivity of these sera with histone H1 zero, a variant found in terminally-differentiated cells such as neurons. This study suggests a potential for histones to serve as autoantigens in humorally-mediated paraneoplastic diseases.

Variable region genes of anti-histone autoantibodies from a MRL/Mp-lpr/lpr mouse

The variable region nucleotide sequences of seven (five IgM and two IgG) anti-histone monoclonal antibodies from a single MRL/Mp-lpr/lpr mouse have been determined. These antibodies are not clonally related and used diverse V, D and J genes. However, six of the seven antibodies have VH segments encoded by genes from the J558 family, two of these (an IgM and an IgG) share an identical VH gene. The isoelectric points of MRA3 and MRA12, the two IgG antibodies of the panel, range from 6.3 to 7.0 and from 6.0 to 6.3, respectively. The second conplementarity-determining region (CDR) of the VH gene of MRA12 (the most acidic and the most strongly histone-reactive antibody) includes only two positively charged but five negatively charged amino acid residues. This feature is unusual since the equivalent CDR in most VHJ558 genes are not comprised predominantly of acidic residues and suggests that such negatively charged residues are important for antibody binding to histones.

Human response against NP-4, a mouse antibody to carcinoembryonic antigen: human anti-idiotype antibodies mimic an epitope on the tumor antigen

Anti-idiotype antibodies (Ab2) were purified from a cancer patient treated with NP-4, a murine monoclonal antibody to carcinoembryonic antigen (CEA). These Ab2 were specific for NP-4 and inhibited the binding between NP-4 and CEA. BALB/c mice immunized with these human Ab2 produced anti-Ab2 antibodies that were also reactive with the CEA epitope recognized by NP-4. These results indicate that human Ab2 to NP-4 can antigenically mimic the CEA epitope recognized by NP-4.

Antihistone antibodies in antinuclear antibody-positive juvenile arthritis

The binding of antinuclear antibody-positive juvenile arthritis (JA) sera to bovine thymus histones H1, H2A, H2B, H3, and H4 was studied by an enzyme-linked immunosorbent assay. Seventy-five percent of the JA patients tested positive for at least 1 antibody specificity. Antihistone antibodies were predominantly IgM, while IgG antibodies were less common and were restricted to histones H1 or H3. In the group of patients with JA of pauciarticular onset, antihistone antibodies were significantly more elevated in patients with past or present uveitis than in patients without a history of uveitis. Anti-H1 antibodies in JA patients were found to react mostly with determinants located in the carboxyl-terminal domain of the H1 molecule. Sera were also reactive with human histone H1(0) or chicken histone H5, which are H1 variants found only in nondividing cells.

Baboon anti-idiotype antibodies mimic a carcinoembryonic antigen epitope

A baboon was immunized with NP-4, a murine monoclonal antibody (MAb) to carcinoembryonic antigen (CEA). Anti-idiotype antibodies were purified from the baboon serum by affinity chromatography on a NP-4-coupled matrix, followed by adsorption of the non-specific antibodies on an irrelevant MAb. Baboon anti-idiotype antibodies inhibited specifically the binding between NP-4 and CEA. Mice immunized with baboon anti-idiotype antibodies produced antibodies to the CEA epitope recognized by NP-4. These results indicate that baboon anti-idiotype antibodies functionally mimic a CEA epitope and that they can be suitable for idiotype therapy of human CEA-producing carcinomas.

Specificities of IgM and IgG anti-histone H1 autoantibodies in autoimmune mice

Autoantibodies to histone H1 represent the most common specificity among anti-histone autoantibodies in systemic autoimmune diseases. Here we analyse anti-H1 autoantibodies in mice from the following autoimmune strains: MRL/Mp-lpr/lpr, NZB and NZB x NZW/F1. Autoantibodies of the IgM isotype bind predominantly to epitopes located in the COOH-terminal domain of the H1 molecule, whereas IgG autoantibodies in the MRL/Mp-lpr/lpr and NZB strains also recognize epitopes requiring the integrity of both the COOH-terminal and the central globular domains of H1. In both of these strains, the titre of these IgG anti-H1 antibodies rises during the course of the disease. The importance of three-dimensional structure of histone H1 was attested by a significant decrease in IgG binding after cleavage of the H1 molecule within the folded globular domain. The binding of these sera to H1 variants from various species was also investigated and a strong binding of MRL/Mp-lpr/lpr sera to certain phylogenetically distant histone H1 variant molecules (sea-urchin sperm H1 and chicken erythrocyte H5) was observed. This cross-reacting binding can be explained by the presence in MRL/Mp-lpr/lpr sera of autoantibodies to H1(0), a variant found in non-dividing cells and exhibiting sequence homologies to the above mentioned variants. The significance and the possible implications of these data for the pathogenesis of autoimmunity are discussed.