A unique monoclonal antibody derived from a lupus-prone mouse with multiple bindings to autoantigens associated with rheumatic disease

Induction of autoantibodies in normal mice by injection of nucleobindin and natural occurrence of antibodies against nucleobindin in autoimmune MRL/lpr/lpr mice

Our previous works have shown that nucleobindin (Nuc) or recombinant (r) Nuc not only augments anti-DNA antibody production in vitro but also accelerates autoimmune response in vivo in MRL/+/+ (MRL/n) mice which are the substrain of autoimmune MRL/lpr/lpr (MRL/l) mice. To investigate whether rNuc can induce autoimmune response similarly in naive mice, we carried out intraperitoneal (i.p.) injection of rNuc (5 micrograms) without adjuvant into 8-week-old female BALB/c mice and continued injection twice a week for 12 weeks. About 5 weeks after the first injection, all the mice began to show IgG hypergammaglobulinemia (HG) followed by elevation of a number of autoantibodies of the IgG class such as anti-double-stranded (ds) DNA, anti-U1 ribonuclear protein (RNP), anti-ssB(La) and anti-Fc antibodies (RF), but not by anti-Sm antibodies. However, the IgG anti-dsDNA antibody response and histopathological changes in the kidney of these BALB/c mice were not so noticeable as those in MRL/n mice induced by rNuc in our previous experiment. In contrast, the IgG anti-rNuc antibody response of normal BALB/c mice induced by rNuc was stronger than that of MRL/n mice induced by rNuc. Since the titers of each autoantibody of BALB/c mice induced by rNuc were not always associated with the level of IgG HG, and either IgG HG or IgG autoantibodies could not be induced by control administration of extracts (5 micrograms) of Escherichia coli with or without harboring plasmid alone, polyclonal B cell activation (PBA) appeared not to be the mechanism of this autoimmunity.(ABSTRACT TRUNCATED AT 250 WORDS)

Novel autoimmune phenomena induced in vivo by a new DNA binding protein Nuc: a study on MRL/n mice

We previously purified a 55 kDa protein that preferentially expands anti-DNA antibody production both in vitro and in vivo across the H-2 barrier from culture supernatants of KML1-7 cells, cloned from a lupus-prone MRL/lpr mouse. By using the purified protein, termed nucleobindin (Nuc), we cloned cDNA and produced recombinant(r) Nuc in Escherichia coli. To elucidate the function of rNuc in vivo, we initially injected intraperitoneally 5 micrograms of rNuc without adjuvant into female MRL/n mice at 8 weeks of age and continued injection twice a week. As early as 5 weeks after administration, all mice treated showed an increase in IgG anti-double stranded (ds) DNA antibodies accompanied by IgG hypergammaglobulinemia (HG). Of particular interest was that these mice also produced anti-U1RNP antibodies and rheumatoid factor (RF) of IgG class, but not anti-Sm antibodies. Histopathologically, hypercellularity with occasional crescents in the glomeruli was observed, but evidence for lupus nephritis was lacking, indicating that some factors other than Nuc are necessary for the development of a lupus syndrome observed in MRL/lpr mice. Similar administration of lipopolysaccharide into MRL/n mice failed to induce autoantibodies except for a slight increase in serum IgG, suggesting that these autoimmune responses are not due simply to polyclonal B-cell activation. The presence of rNuc will give us a clue for further understanding of autoimmunity.

Purification of a novel B cell growth and differentiation factor associated with lupus syndrome

We have previously reported that KML1-7 cells cloned from a lupus-prone MRL/l mice produced a soluble factor that preferentially expanded anti-DNA antibody production across the H-2 barrier. We purified this factor, a 55-kDa protein that we termed nucleobindin (Nuc). Nuc showed not only induction of anti-ssDNA IgG antibody in cultures of B cells from MRL/l mice (greater than 16 weeks old), but also growth activity. Furthermore, antibodies against existing cytokines have so far not been shown to block Nuc activity on these B cells. In view of the fact that Nuc did not boost anti-ssDNA IgG antibody production in cultures of spleen cells of comparable age from MRL/n mice, which develop a mild form of lupus after the age of one year, Nuc may act on pre-activated B cells to help IgG anti-DNA antibody production. Taken together, Nuc is a new kind of growth and differentiation factor associated with lupus syndrome.

Double reactivity of monoclonal and polyclonal rheumatoid factors for IgG and histones: Mapping of binding sites by means of histone synthetic peptides and anti-Id antibodies

Polyreactive antibodies able to bind various apparently unrelated structures represent a frequent antibody population in autoimmune diseases. In this work, the structural basis of the double reactivity of such autoantibodies was investigated using as models polyclonal and monoclonal human rheumatoid factors (RF) reacting with histones. Both direct ELISA binding and competitive inhibition experiments were performed. A more precise delineation of the histone regions recognized by the RFs was made by means of 27 synthetic peptides of these proteins. Anti-idiotope (Id) murine antibodies were used to map the binding sites involved on RF in the interaction with IgG and histones. Among the 13 polyclonal and six monoclonal RFs tested, four and two respectively were found to cross-react with IgG and histones. The fragments shown to be the most frequently recognized by RFs were located in residues 1-16 and 204-218 of H1, 1-20 and 65-85 of H2A, and 1-21 of H3. The results obtained by competitive ELISA assays using IgG, histone peptides and anti-Id monoclonal antibodies led us to confirm and characterize more precisely our previous finding suggesting the existence of topographically distinct binding sites for the different targets recognized by RFs.

Polyanions inhibit binding of human autoantibodies to certain cellular proteins

The effect of polyanions on the reactivity of human autoantibodies with cellular proteins was studied. The results of immunoblotting revealed that dextran sulfate (DS), heparin, single-stranded (ss) DNA, and polyinosinic acid (poly I) inhibit interaction between immunoglobulins (Ig) from human autoimmune sera and many polypeptides with various molecular mass. These proteins were suggested to belong to a new subclass of autoantigens, the immunoreactivity of which is sensitive to the presence of polyanions. For some of these antigens, molecular mass, intracellular localization and frequency of appearance of positive sera were determined.

Temporary breakdown of immunological tolerance to dsDNA and nucleohistone antigens in rabbits infected with rinderpest virus

The rabbit-passaged L strain of rinderpest virus (RV) causes the transient induction of anti-nuclear antibodies (ANA) in rabbits. It has been shown by an indirect immunofluorescence test that the target antigens of these ANA are DNA and/or DNA-histone complexes (nucleohistone). Here detailed examinations of the target antigens were carried out by ELISA, and it was revealed that rabbit sera contained three types of antibodies: antibodies reacting equally with both dsDNA and ssDNA; those reacting with ssDNA alone; and those reacting with nucleohistone. Epitopes recognized by the third type consisted of complexes of dsDNA and H2A + H2B or of dsDNA and H2B. All types of antibodies were antigen specific. Since the diversity of ANA among experimental rabbits was large, it was suggested that genetic background is important in the induction of anti-dsDNA antibodies in this system. Moreover, early induction of antibodies to nucleohistone and the rapid disappearance of ANA suggest that B cell proliferation/maturation for continuous production of ANA requires factors other than RV infection. This system may help elucidate the mechanisms of ANA induction and the development of autoimmune diseases.

Anti-DNA antibodies and lupus nephritis: the complexity of crossreactivity

It has been suggested that crossreactivity of anti-DNA antibodies plays a central role in the development of lupus nephritis. Experiments with monoclonal anti-DNA antibodies initially seemed to sustain this intriguing hypothesis but such studies may easily lead to incorrect conclusions. In this short article, Kees Brinkman and colleagues discuss the validity of these studies and challenge the role of crossreactivity in the pathogenesis of lupus nephritis.

Early induction of anti-double-stranded DNA antibodies in lupus-prone MRL mice inoculated with Ly-24+ cells cloned from lymph node cells of an MRL/Mp-lpr/lpr mouse: possible effect of putative cytokines produced by cloned Ly-24+ cells

We have reported that a cell line, KML1, obtained from lymph node cells of a 16-week-old female MRL/Mp-lpr/lpr (MRL/1) mouse produces a soluble factor(s) that promotes formation of anti-single-stranded (ss) DNA antibodies by cultures of spleen cells from old MRL/l mice (greater than 16 weeks old). Detailed examination revealed that KML1-7 cells cloned from the cell line KML1 were only positive for the Lys-24 (Pgp-1) phenotype, and were negative for other typical phenotypes tested, such as Thy-1, Ly-1, Ly-2, Ly-4 (L3T4) and Ly-5 (B220). This finding suggested that this line was of prothymocyte or myeloid cell lineage. From day 70 after subcutaneous inoculation of KML1-7 cells into 10-week-old MRL/Mp(-)+/+(MRL/n) mice, IgG anti-dsDNA antibodies began to replace IgM anti-dsDNA antibodies in the serum of these mice, but anticardiolipin, anti-trinitrophenyl hapten (TNP) and anti-poly(ADP-ribose) antibodies did not increase significantly. The predominant subclasses of anti-dsDNA antibodies that increased were IgG2a and IgG2b. IgG anti-dsDNA antibodies also became detectable as early as day 22 after inoculation of KML1-7 cells into MRL/l mice of 10 weeks old. The finding that in MRL/n mice the IgM isotype was increased first and was soon replaced by the IgG isotype was consistent with findings when spleen cells from MRL/n mice of 20 weeks old primed with ssDNA were cultured in the presence of conditioned medium containing a putative cytokine(s) (PC) produced by KML1-7 cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Interpretation of the cross-reactivity of anti-DNA antibodies with cell surface proteins: the role of cell surface histones

The putative cross-reaction of anti-DNA antibodies with "lupus-associated membrane proteins (LAMP)" on the surface of intact Raji cells was examined by sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) and immunoblotting analyses. Cell surface proteins of 14, 17, 18, 33 and 34 kDa were detected by monoclonal anti-double-stranded (ds) DNA antibodies and the sera of patients with systemic lupus erythematosus (SLE) in active states, but were not detected by the sera of SLE patients in inactive states, nor in healthy controls. However, pre-treatment of these anti-DNA antibodies with DNase I markedly reduced the reactivity to the cell surface proteins. Judging from the electrophoretic mobility, these proteins were identical with histones, and purified histones inhibited the reaction of anti-DNA antibodies with the cell surface proteins. Moreover, affinity-purified antihistone antibodies could demonstrate histones in the Raji cell surface proteins. Thus, we conclude that "cross-reaction" of anti-DNA antibodies with LAMP is due to DNA-anti-DNA immune complexes which could react with cell surface histones.

In vivo cytokine gene expression in T cell subsets of the autoimmune MRL/Mp-lpr/lpr mouse

Expression of cytokine genes in freshly isolated T cell subsets in the autoimmune lpr mouse has been studied to determine what factors may be produced by these cells in vivo. RNA prepared from T cell subsets from diseased lpr mice and from the normal congenic strain, MRL/n, was tested for the presence of cytokine-specific message using the polymerase chain reaction. Cells of the expanded abnormal T cell subset were shown to express genes encoding interferon (IFN)-gamma, tumor necrosis factor (TNF)-beta, TNF-alpha and interleukin (IL)6, cytokines which are associated with inflammatory immune responses. These cells may thus play an important role in exacerbation of the pathological symptoms of the systemic autoimmune disease. These cells expressed no detectable IL1, IL2, IL3, IL4 or IL5. Phenotypically normal CD4+ and CD8+ T cells from both lpr and MRL/n also contained transcripts for IFN-gamma, TNF-alpha, TNF-beta and IL6. IL2 mRNA was found almost exclusively in the CD4+ subset, indicating that the CD8+ T cells in the lpr mouse are not highly activated through their class I major histocompatibility complex molecules to produce IL2, as could occur if a virus infection was inducing autoimmunity in these mice. Similar levels of IL2 mRNA were present in the CD4+ T cells of lpr and MRL/n mice, demonstrating that these cells are not defective in IL2 production in vivo.

A novel trait of naturally occurring anti-DNA antibodies: dissociation from immune complexes in neutral 0.3-0.5 M NaCl

Monoclonal and polyclonal anti-DNA antibodies from autoimmune mice, and experimentally induced rabbit anti-nucleic acid polyclonal antibodies were tested for stability of binding to nucleic acids in the presence of various concentrations of NaCl by an enzyme-linked immunosorbent assay (ELISA). Murine monoclonal antibodies 2C10 (IgG2b) and 1A2 (IgG2a), which are known to react specifically with double-stranded (ds) DNA, dissociated completely from their complexes with DNA when washed with a neutral 0.5 M NaCl solution. Another monoclonal antibody (MoAb) (IgM,kappa), polyreactive with single-stranded (ss) DNA, cardiolipin, and trinitrophenylhapten (TNP), was also dissociated from its complexes with ss DNA, but not from its complexes with TNP, by 0.3-0.5 M NaCl. Similar differences were observed in the binding stability of serum antibodies from autoimmune mice to DNA and TNP. In contrast, anti-nucleic acid polyclonal antibodies induced in rabbits by immunization with poly(I), poly(dT) or poly(ADP-ribose) were not significantly dissociated from their immune complexes with relevant antigens or DNA by 0.5 M NaCl. The finding that nucleic acid antigens were not detached from a solid phase by washing with 0.5 M NaCl solution indicated that the reduction of binding of anti-DNA antibodies in both MoAbs and naturally occurring antibodies was really due to dissociation of the antibodies from immune complexes. This is the first demonstration that DNA epitopes recognized by naturally occurring antibodies in both SLE and its mouse models are sensitive to neutral NaCl concentrations. This novel trait of naturally occurring antibodies will be very useful in studies on the nature of immune complexes in sera and kidneys of cases of systemic lupus erythematosus (SLE).

Cross-reactive binding patterns of monoclonal antibodies to DNA are often caused by DNA/anti-DNA immune complexes

Recently, the role of antibodies to DNA in the pathogenesis of systemic lupus erythematosus (SLE) has been reevaluated, since observed cross-reactive binding of anti-DNA to tissue-related antigens might substantially contribute to the inflammatory process of the disease. Evidence of this cross-reactivity has, in part, been obtained from studies with monoclonal anti-DNA. However, we now report that the presence of DNA/anti-DNA immune complexes in monoclonal antibody preparations may be the cause of the observed cross-reactive binding patterns. Studying a panel of anti-DNA producing hybridomas (n = 63), we detected such immune complexes in 76% of the obtained culture supernatants by using an anti-protamine sulphate (PS) ELISA; complexes formed with 1 microgram/ml DNA or more were traced in this assay. In cultures of anti-DNA-producing hybridomas, complexes were detected from day 3 on. Treatment of supernatants with DNase reduced the anti-PS reactivity to an average of only 20% of the original reactivity. Contaminating DNA/anti-DNA immune complexes were found to play no role in the cross-reactivity of anti-DNA antibodies with cardiolipin, a minor role in cross-reactivity with dextran sulphate, but a substantial role in the cross-reactivity with heparan sulphate, histones and other nuclear or cytoplasmic antigens. Our results clearly demonstrate that exclusion of the presence of immune complexes in antibody preparations is a prerequisite when cross-reactivity patterns of anti-DNA antibodies are studied.

Lupus erythematosus cell formation by a monoclonal antibody derived from an autoimmune MRL/Mp-lpr/lpr mouse

An MRP-2 monoclonal antibody (MoAb) was primarily a product of hybridoma selected by binding to poly(ADP-ribose) from a lupus prone MRL/Mp-lpr/lpr (MRL/l) mouse, and was shown to cross-react with single-stranded (ss) DNA. Detailed examination revealed that MRP-2 MoAb bound to a conformational epitope formed between double-stranded (ds) DNA and total histone: both H3 and H4 were essential for the formation of this conformational epitope with dsDNA. Because of this characteristic of the MoAb, its ability to induce lupus erythematosus (LE) cells was examined in an indirect LE test with peripheral blood of MRL/Mp-+/+ (MRL/n) mice, which develop a mild form of lupus after the age of one year. MRP-2 MoAb was found to induce hematoxylin bodies, LE rosettes and LE cells, but a direct LE test using MRL/n mouse blood did not induce LE cell phenomena. This is the first demonstration of induction of LE cells by a MoAb that binds to dsDNA-histone complexes.