Autoantibodies of various specificities encoded by genes from the VH J558 family bind to foreign antigens and share idiotopes of antibodies specific for self and foreign antigens

Polyspecificity of Anti-lipid A Antibodies and Its Relevance to the Development of Autoimmunity

The process of natural selection favours germ-line gene segments that encode CDRs that have the ability to recognize a range of structurally related antigens. This presents an immunological advantage to the host, as it can confer protection against a common pathogen and still cope with new or changing antigens. Cross-reactive and polyspecific antibodies also play a central role in autoimmune responses, and a link has been shown to exist between auto-reactive B cells and certain bacterial infections. Bacterial DNA, lipids, and carbohydrates have been implicated in the progression of autoimmune diseases such as systemic lupus erythematosus. As well, reports of anti-lipid A antibody polyspecificity towards single-stranded DNA together with the observed sequence homology amongst isolated auto- and anti-lipid A antibodies has prompted further study of this phenomenon. Though the lipid A epitope appears cryptic during Gram-negative bacterial infection, there have been several reported instances of lipid A-specific antibodies isolated from human sera, some of which have exhibited polyspecificity for single stranded DNA. In such cases, the breakdown of negative selection through polyspecificity can have the unfortunate consequence of autoimmune disease. This review summarizes current knowledge regarding such antibodies and emphasizes the features of S1-15, A6, and S55-5, anti-lipid A antibodies whose structures were recently determined by X-ray crystallography.

Structural Basis for Antibody Recognition of Lipid A: INSIGHTS TO POLYSPECIFICITY TOWARD SINGLE-STRANDED DNA

Septic shock is a leading cause of death, and it results from an inflammatory cascade triggered by the presence of microbial products in the blood. Certain LPS from Gram-negative bacteria are very potent inducers and are responsible for a high percentage of septic shock cases. Despite decades of research, mAbs specific for lipid A (the endotoxic principle of LPS) have not been successfully developed into a clinical treatment for sepsis. To understand the molecular basis for the observed inability to translate in vitro specificity for lipid A into clinical potential, the structures of antigen-binding fragments of mAbs S1-15 and A6 have been determined both in complex with lipid A carbohydrate backbone and in the unliganded form. The two antibodies have separate germ line origins that generate two markedly different combining-site pockets that are complementary both in shape and charge to the antigen. mAb A6 binds lipid A through both variable light and heavy chain residues, whereas S1-15 utilizes exclusively the variable heavy chain. Both antibodies bind lipid A such that the GlcN-O6 attachment point for the core oligosaccharide is buried in the combining site, which explains the lack of LPS recognition. Longstanding reports of polyspecificity of anti-lipid A antibodies toward single-stranded DNA combined with observed homology of S1-15 and A6 and the reports of several single-stranded DNA-specific mAbs prompted the determination of the structure of S1-15 in complex with single-stranded DNA fragments, which may provide clues about the genesis of autoimmune diseases such as systemic lupus erythematosus, thyroiditis, and rheumatic autoimmune diseases.

Navigating the passage between Charybdis and Scylla: recognizing the achievements of Noel Rose

This special edition of the Journal of Autoimmunity is dedicated to celebrate the enormous contributions of Dr. Noel Rose, a physician-scientist, someone that can be readily anointed as a gifted scientist who laid down the foundation and fundamental concepts of human autoimmunity. Dr. Rose performed a series of landmark studies that extend back more than 50 years and whose work is the cornerstone of the commonly used term "from the bench to the bedside." The studies included not only characterization of a normal immune response but, more importantly, defining the nature of not only the antigen, but also the aberrant response that results in organ, tissue specific reactions and immunopathology. These pioneering studies contributed to the biochemical nature of antigens, dissection of the immune repertoire, the recognition of the importance of genetics and environment, and the distinctions between a normal and an autoimmune response. Hence, this volume has been coined "Navigating the Passage Between Charybdis and Scylla: Recognizing the Achievements of Noel Rose."

GADD45a is a novel candidate gene in inflammatory lung injury via influences on Akt signaling

We explored the mechanistic involvement of the growth arrest and DNA damage-inducible gene GADD45a in lipopolysaccharide (LPS)- and ventilator-induced inflammatory lung injury (VILI). Multiple biochemical and genomic parameters of inflammatory lung injury indicated that GADD45a(-/-) mice are modestly susceptible to intratracheal LPS-induced lung injury and profoundly susceptible to high tidal volume VILI, with increases in microvascular permeability and bronchoalveolar lavage levels of inflammatory cytokines. Expression profiling of lung tissues from VILI-challenged GADD45a(-/-) mice revealed strong dysregulation in the B-cell receptor signaling pathway compared with wild-type mice and suggested the involvement of PI3 kinase/Akt signaling components. Western blot analyses of lung homogenates confirmed approximately 50% reduction in Akt protein levels in GADD45a(-/-) mice accompanied by marked increases in Akt ubiquitination. Electrical resistance measurements across human lung endothelial cell monolayers with either reduced GADD45a or Akt expression (siRNAs) revealed significant potentiation of LPS-induced human lung endothelial barrier dysfunction, which was attenuated by overexpression of a constitutively active Akt1 transgene. These studies validate GADD45a as a novel candidate gene in inflammatory lung injury and a significant participant in vascular barrier regulation via effects on Akt-mediated endothelial signaling.

T-cell enforced invariance of the antibody repertoire in the immune response against a bacterial carbohydrate antigen

The humoral response against the bacterial polysaccharide antigen alpha(1-->3) dextran (Dex) is controlled by J558 idiotype-(Id) specific T cells. These T cells of which the cell clone 178-4 Ts is a representative by all relevant criteria, recognize J558 Id-bearing B cells in an I-Ed-restricted manner. Costimulation via CD28/B7-1 but not via CD40/CD40L leads to T-cell activation. These T cells do not only suppress B cells producing the immunoglobulin (Ig)G3 isotype but also support the survival and clonal expansion of J558 Id positive B cells both in vivo and in vitro. This T-cell mediated dominance of the J558 idiotype limits the appearance of antibodies carrying other more diverse idiotypes which appear in immunized BALB/c nu/nu mice where no regulatory T cells occur. This T-cell mediated antibody invariance could be a strategy of the immune system responding to highly conserved antigens like polysaccharides, different from those against protein antigens, where diversity is assumed to be the basis for a successful response.

Two-dimensional electrophoresis and mass spectrometry identification of proteins bound by a murine monoclonal anti-cardiolipin antibody: a powerful technique to characterize the cross-reactivity of a single autoantibody

Antigenic cross-reactivity, i.e., the capacity of a single antibody to react with apparently dissimilar structures, is a common characteristic of autoantibodies produced during systemic lupus erythematosus (SLE), an autoimmune disease developed by humans and certain strains of mice. Characterization of the extent of cross-reactivity of SLE-related autoantibodies may help identify the immunogenic stimulus, or stimuli, of autoantibody-secreting B-lymphocytes. Two-dimensional polyacrylamide gel electrophoresis (2-D PAGE) was combined with mass spectrometry (MS) to identify cell proteins recognized by a single monoclonal autoantibody (mAb 4B7), derived from an (NZW x BXSB)F1 mouse and selected based on its capacity to react with cardiolipin, that binds to elements in the cytoplasm and nucleoli of HEp-2 cells as assessed by indirect immunofluorescence assay. Proteins from HL-60 extract were separated by 1-D and 2-D PAGE. Western blotting with mAb 4B7 after SDS-PAGE revealed four bands, two intensely labeled at 35 and 32 kDa, and two weaker ones at 20 and 60 kDa; three spots were detected after 2-D PAGE. After trypsin in-gel digestion of the three protein spots, MS yielded representative matrix assisted laser desorption/ionization-time of flight (MALDI-TOF) Reflector or quadrupole-time of flight (Q-TOF) spectra. The three corresponding proteins were identified as the nucleolar phosphoprotein B23 (nucleophosmin), heterogeneous nuclear ribonucleoprotein A2 (hnRNP A2) and the 60 kDa Ro/SS-A RNP. Thus, these results showed that 2-D PAGE combined with MS constitutes a sensitive and powerful technique to characterize the full extent of cross-reactivity of a single mAb and may constitute a new approach to further characterize the immunogenic cellular components involved in the breakage of B-cell tolerance observed in SLE.

Antibodies with idiotypic and anti-idiotypic reactivity (epibodies) in conventional immune responses to dinitrophenylated carriers

A number of monoclonal antibodies were derived from the spleen cells of dinitropheryl (DNP)-immunized mice. Both T-dependent and T-independent carriers were used, and the intensity and length of immunization were varied. It was found that some of the antibodies had only idiotypic (Ab1) reactivity, while others had both idiotypic (Ab1) and anti-idiotypic (Ab2) reactivity. Among the latter antibodies some molecules reacted specifically with DNP and with the combining site of anti-DNP antibodies (epibodies), while others bound DNP and anti-DNP Abs as well as a variety of unrelated antigens (polyreactive antibodies). The proportion of the three types of antibodies (antigen-specific, epibodies and polyreactive antibodies) varied with the nature of the carrier, the intensity of the immunization, and the length of the immunization process. Further characterization of the epibodies, which were predominant in the secondary response to DNP-keyhole limpet haemocyanin (KLH), showed that both Ab1 and Ab2 reactivities were inhibited by both soluble ligands (DNP and anti-DNP), indicating that the specific combining site of the monoclonal antibodies (mAbs) (and/or of the rabbit anti-DNP antibody in the case of Ab2) was involved in both activities. Both Ab1 and Ab2 reactivities were removed by absorption of the mAbs with either immobilized DNP or immobilized rabbit anti-DNP. The mAbs were capable of binding themselves as well as to other mAbs with the same characteristics. The affinity constants of several mAbs for both the DNP and anti-DNP ligands were determined.

Monoclonal antibody to heparan sulfate from autoimmune tight skin (TSK) mice binds to the endothelial cell surface

Heparan sulfate proteoglycans have pleiotropic functions in the normal vasculature. Autoimmunity to heparan sulfate may play a role in vascular injury. In this study, monoclonal antibody (mb) 28C3-1 to heparan sulfate derived from autoimmune Tight skin (TSK) mice was investigated for its reactivity with endothelial cells. Mb 28C3-1 was previously demonstrated to inhibit the heparin-accelerated formation of antithrombin III-thrombin complexes. In the current studies it is shown that mAb 28C3-1 bound to heparan sulfate proteoglycan with the highest affinity in direct binding solid phase radioimmunoassay. Binding to the heparan sulfate was stronger than binding to the protein core, indicating that the primary epitope of 28C3-1 is the polysaccharide component. Using confocal fluorescent microscopy, mAb 28C3-1 was demonstrated to bind to the endothelial cell surface. Furthermore, treatment of endothelial cells with heparitinase abolished mAb 28C3-1 binding. These studies support the hypothesis that naturally occurring anti-heparan sulfate autoantibodies from autoimmune mice may cause vascular injury by initial interaction with endothelial cell surface heparan sulfate.

Molecular heterogeneity of antigen- or idiotype-induced anti-thyroglobulin monoclonal autoantibodies

To define the molecular basis of the cognitive interaction in experimental autoimmune thyroiditis (EAT), we sequenced the variable regions of monoclonal autoantibodies to thyroglobulin (Tg), specific or not for the F40D peptide, a Tg peptide capable of inducing EAT in CBA/J mice. Three MoAbs were obtained by immunization with syngeneic Tg of CBA/J (3B8G9, 2F6F2) or C57Bl/6 (4D11F4) mice. 3B8G9 was specific for F40D peptide, whereas 2F6F2 and 4D11F4 were not. Two others were raised in CBA/J mice by manipulation of idiotypic pathways: B12 resulted from the immunization with one Ab2 beta, bearing the internal image of one F40D epitope, and TA2 from the immunization with F40D-specific cytotoxic HTC2 T cells. B12 and TA2 were both specific for F40D. All hybridomas expressed different members of the J558 VH family, except 3B8G9 which expressed a Q52 VH gene segment. These data led us to hypothesize that regulatory anti-id autoantibodies used members of one VH family located in the 5'-end of the VH locus, whereas EAT-associated autoantibodies used a member of one of the most D-proximal VH family. As expected, no homologies were found when anti-F40D monoclonal autoantibodies were compared with two other monoclonal autoantibodies displaying a different epitopic specificity. Among the anti-F40D monoclonal autoantibodies, one histidine residue located in position 35 of the CDR1 region was constantly found. Moreover, TA2 and B12 exhibited two common amino acids in their CDR3 regions, one glycine and one tyrosine, in positions 98 and 99, respectively. Striking homologies were found between TA2 and one anti-polyGAT MoAb, and between 3B8G9 and some anti-phenyloxazolone (phOx) monoclonal autoantibodies. Lastly, the VK sequence from 4D11F4 was identical at the amino acid level to the VK sequence from another monoclonal autoantibody, 81B1, which was previously raised towards syngeneic Tg in CBA/J mice. Our data imply that anti-idiotypic regulatory circuits in EAT might be generated by a heterogeneous population of B cells rather than obtained by a single dominant B cell population.

Regulation of an anti-polysaccharide immune response in BALB/c mice through a tight T and B lymphocyte idiotypic connection

The isotype expression in the J558 idiotype-associated humoral immune response against alpha(1-->3)-dextran in BALB/c mice is controlled by idiotype-specific T cells which silence in situ B lymphocytes primed and committed to an IgG response. This leads to a restriction of the type II thymus-independent response to the sole production of IgM antibodies. The availability of the T cell receptor (TcR) alpha and beta sequences for such a regulatory T cell clone allows the investigation of the degree of heterogeneity of the TcR usage of these T cells. It is found that all alpha(1-->3)-dextran-primed BALB/c mice use a very similar, possibly identical TcR. This suggests a tight, possibly genetically programmed, interaction between the J558 idiotype-bearing dextran-specific B cells and their idiotype-specific regulatory T cell counterparts.

Increased utilization of polyreactive B cells during periods of generalized immune activation

This work examines the hypothesis that B cells secreting polyreactive antibodies (antibodies capable of binding to more than one self or foreign antigen) are preferentially utilized during periods of generalized immune stimulation. Four conditions characterized by such stimulation were examined: chronic virus infection, mitogen treatment, autoimmune disease and neonatal repertoire development. In normal adult mice, polyreactive IgM secreting lymphocytes constituted 8-9% of the actively expressed repertoire. Under conditions of generalized immune activation, this frequency increased to 13-19% (p. < .01). Polyreactive IgG secreting B cells, which were present at frequencies of < 0.5% in normal adult mice, were found at freqeuncies of 6-10% in mice with autoimmune disease, chronic virus infection or following mitogen treatment (p. < .001). We postulate that polyreactive lymphocytes are preferentially activated when the immune system is confronted with stimuli inadequately controlled by antigen-specific responses.

Cross-reactivity of IgM- and IgG-secreting B cells in autoimmune mice

OBJECTIVE

To determine the frequency with which in vivo-activated B cells secrete cross-reactive antibodies in lupus-prone mice.

METHODS

Analysis of freshly isolated splenic lymphocytes by chamber enzyme-linked immunospot assay.

RESULTS

Young New Zealand black, New Zealand black x New Zealand white, and MRL/lpr mice expressed repertoires in which 16-20% of IgM-secreting cells and 0-2% of IgG-secreting cells were cross-reactive. By comparison, 21-31% of IgM- and 4-14% of IgG-secreting cells in adult animals with active lupus were cross-reactive (P < 0.01).

CONCLUSION

Cross-reactive B cells constitute an abnormally large proportion of the repertoire expressed in mice with active autoimmune disease.

A possible paradox in the immunology of multiple sclerosis: its apparent lack of 'specificity' might provide clues to the etiology

As a further development from an earlier hypothesis, a pathogenic role of polyspecific natural, idiotypically connected antibodies is claimed, that recognize concomitantly a variety of CNS antigens and are matured to some degree to higher-affinity anti-CNS antibodies without ever losing their network association. On that basis, nitrophenol-carrier conjugates well-known to be foreign target antigens of natural antibodies and present in food commodities that have epidemiological links to MS, are considered as paradigmatic for agents of possible etiologic importance.

Characterization of idiotype-specific I-Ed-restricted T suppressor lymphocytes which confine immunoglobulin class expression to IgM in the anti-alpha (1- > 3) Dextran B 1355 S response of BALB/c mice

The humoral immune response of conventionally raised BALB/c mice to the so-called "thymus independent" antigen alpha (1- > 3) Dextran B 1355 S (Dex) is predominantly of the IgM class. The response is further characterized by Igha allotype linkage and the dominance of the public idiotypes (Id) J558 and MOPC 104. In germfree raised BALB/c and in BALB/c nu/nu mice immunized with the same antigen an additional IgG response of the public Id is observed. Analysis of the regulation of the class expression reveals existence of specific Ts cells in euthymic mice which must have been activated pre- or perinatally by exposure to environmental bacterial antigens. They permit or enforce differentiation of Dex-specific B cells into B gamma memory cells without allowing further development into IgG producing plasma cells. An analogue of these splenic Ts cells has now been cloned and identified as an I-Ed restricted Id-specific T cell with exactly the properties ascribed above to the splenic Ts cells. This paper describes phenotypical and functional properties of the Ts cell clone 178-4. It evaluates this clone's role in controlling efficient anti-bacterial IgM-mediated immunity under conditions where a class switch to IgG antibody production is actively suppressed; possibly as a measure to avoid hazardous autoimmune reactions on the basis of crossreaction and antigenic mimicry between polysaccharide antigens.

Correlation of antibody multireactivity with variable region primary structure among murine anti-erythrocyte autoantibodies

A high proportion of the antibodies in the preimmune repertoire bind to several unrelated antigens and are considered to be multireactive. This property is reportedly associated with the antibodies produced by CD5+ B lymphocytes. Because many antibodies specific for bromelain-treated mouse red blood cells (BrMRBC) derive from CD5+ B cells, we tested monoclonal antibodies of this specificity for multireactivity. Two variable region combinations, VH11/V kappa 9 and VH12/V kappa 4, account for greater than 80% of this repertoire, but none of these antibodies exhibited a multireactive phenotype. In contrast, three anti-BrMRBC binding antibodies belonging to the J558 family (BrM1, BrM8, and CH12) showed varying degrees of multireactivity, and bound both highly negatively and positively charged antigens. The amino acid sequences of the VH regions of these antibodies are highly homologous (greater than 85% identical) and they possess large VH-D-J junctions with extensive N-region insertions. The kappa chains of two of these antibodies utilize an identical V kappa gene segment, while the third uses a very different V kappa with only 50% homology. The entire H chain V regions of these antibodies are unusually basic, with isoelectric points of 9.5-10, a feature which might be important in promoting interactions with acidic epitopes. The multireactive antibodies also contain regions with a high concentration of hydroxylside chain amino acids, especially in their VH-D-J junctions. This region also contains acidic amino acid residues, which may be important in binding of positively charged epitopes. We propose that an open, accessible binding site and a charge polarity may be features which facilitate the binding of charged epitopes, providing a structural basis for multireactivity of at least some antibodies.

Quantitation of IgM- and IgG-secreting B cells in the peripheral blood of patients with systemic lupus erythematosus

An enzyme-linked immunospot assay was used to quantitate the number of autoantibody-secreting B cells in the peripheral blood of 67 patients with systemic lupus erythematosus. These patients had 1.5-4-fold more lymphocytes secreting IgG and IgM per million peripheral blood lymphocytes than did normal controls. There was a concomitant increase in the number of B cells secreting antibodies reactive with a diverse panel of foreign and self antigens (including actin, myosin, tri-nitrophenylated keyhole limpet hemocyanin, ovalbumin, and retroviral gp160). By comparison, the number of B cells producing anti-DNA antibodies was increased disproportionately. The magnitude of this anti-DNA response correlated significantly with disease activity. Thus, B cell activation in human systemic lupus erythematosus had characteristics of both generalized (polyclonal) B cell activation and (auto)antigen-specific immune stimulation.

Expression of the major rheumatoid factor cross-reactive idiotype in pediatric patients with systemic lupus erythematosus

Rheumatoid factor cross-reactive idiotype (RF-CRI) is expressed in high concentrations in the sera of some patients with rheumatoid arthritis (RA) and juvenile rheumatoid arthritis (JRA). To determine if RF-CRI is specifically expressed in rheumatic disease or if it is secondary to polyclonal B-cell activation, we examined sera of 23 children with SLE, 16 adolescents with infectious mononucleosis (IM), and age-matched pediatric controls for RF-CRI expression. Concentrations of RF-CRI in serum, determined by an inhibition ELISA, were 24 +/- 17 micrograms/ml (mean +/- SD) in 25 normal children, 31 +/- 17 in 16 young adults with IM, and were significantly increased, 70 +/- 80 micrograms/ml, in the 23 children with SLE (p less than 0.036). Eleven of 23 SLE patients had serum RF-CRI greater than the mean +/- 2 SD for normal children. Ten of 23 SLE sera contained IgM rheumatoid factor (RF) activity. One patient with IM had a borderline elevated RF-CRI level, and 5 IM patients had RF in their sera. The serum IgM concentrations in sera were: SLE (192 +/- 93 mg/dl) and IM (234 +/- 77 mg/dl) sera. These levels were significantly elevated compared to controls (132 +/- 44 mg/dl), p less than 0.031 for SLE and p less than 0.001 for IM, suggesting that polyclonal activation of B cells was present in SLE and IM patient groups. Increased expression of RF-CRI in the SLE patients correlated directly with high titer anti-DNA antibody values (r = 0.3965, p less than 0.05) and RF activity when human IgG (r = 0.5026, p less than 0.05) was used as the RF binding substrate and inversely with serum C3 levels (r = 0.3925, p less than 0.05). RF-CRI expression did not correlate with RF that bound rabbit (r = 0.3123, p greater than 0.05). Increased serum RF-CRI expression is not a result of polyclonal B-cell activation. RF-CRI may be selectively up-regulated in patients with SLE.

Evidence for regulation of naturally activated autoreactive B cells

A large fraction of naturally activated B cells in the neonate displays degenerate specificity, including reactivity with autoantigens. Transgenic mouse models of autoreactive B cells are mainly concerned with monospecific B cells of high avidity, and the fate of naturally activated autoreactive B cells is still a matter of debate. To pursue this question further, we chose an IgM autoantibody with a recurrent idiotype (Id), i.e. Sp6, because transgenic mice expressing this IgM also were available. In a first approach monoclonal antibodies (mAb) derived from untreated, antigenically stimulated and transgenic mice were used to test whether there were indications for deletion or for Id regulation of naturally activated autoreactive B cells. Over 90% of thymus and spleen cell derived hybridomas from 6-day-old Sp6-transgenic mice were trinitrophenyl (TNP) reactive, carried the Sp6-Id and bound to a panel of self antigens, including mouse albumin. We failed to obtain B cell hybridomas from the thymus of 28-day-old Sp6-transgenic mice. Furthermore, we could not detect any mAb carrying an anti-Sp6 Id, but Sp6 did weakly bind to itself. About 25% of mAb derived from control mice displayed degenerate specificity, the majority of them also were TNP reactive. The Sp6 Id was found at a low frequency and a comparable number of mAb carried an anti-Sp6 Id. Prenatal manipulation at the antigen level (trinitrobenzenesulfonic acid treatment) led to a transient expansion of TNP- and autoreactive mAb. The number of mAb carrying the Sp6 Id was not increased, but mAb carrying an anti-Sp6 Id were observed at high frequency. Those mAb also displayed degenerate specificity. Since Sp6-transgenic mice were perfectly healthy, it is concluded that this particular autoreactive antibody of degenerate specificity cannot be harmful for the developing organism, which may possibly be due to its self-binding capacity. Furthermore, some process of down-regulation was indicated by the absence of B cells expressing the transgene in the thymus of young adult mice. Autoreactivity of untreated and prenatally antigen-treated mice was, in addition, regulated at the Id level. In particular, mAb recognizing the Id of Sp6 were significantly expanded in antigenically stimulated mice. The data were interpreted in the sense that autoreactive B cells appearing early during ontogeny were rather strictly controlled either by (functional) clonal deletion or by idiotypic connectivity.

Idiotypic profile of natural autoantibodies in newborn and young adult BALB/c mice

Idiotypic profiles of autoreactive monoclonal antibodies (MoAb) were evaluated by their reactivity with a panel of alkaline phosphatase (AP)-coupled detector MoAb derived from the same fusions. Attention was given to the question of whether differences exist between MoAb derived from spleen cells (SC) or thymocytes (TC) and whether ID profiles would change during post-natal development. In the newborn, natural autoantibodies and MoAb which did not react with any one of eight autoantigens displayed different ID profiles, autoreactive MoAb being characterized by the expression of a restricted pattern of ID. During post-natal development, changes of ID expression were only observed with autoreactive MoAb. Many ID which were detected on MoAb derived from 6-day-old mice were not detected on SC-derived MoAb from young adults, while a few ID were significantly over-represented. Furthermore, especially with TC-derived MoAb, a clear linkage between certain idiotypes and autoantigen specificities could be demonstrated. Thus, in contrast to non-autoreactive MoAb, natural autoantibodies in the young adult were characterized by expressing only a selected number of ID at high frequency. Furthermore, the B-cell environment apparently played a role, since there were marked differences between ID profiles of TC- versus SC-derived MoAb. The data are interpreted in the sense that expansion and maturation of naturally activated autoreactive B cells are controlled rather than being random processes.

Self reactive repertoire of tight skin mouse: immunochemical and molecular characterization of anti-topoisomerase I autoantibodies

Tight skin (TSK) mice develop cutaneous hyperplasia accompanied by histopathological alterations of skin and collagen metabolism similar to those described in human scleroderma. Diffuse scleroderma, the most severe form of progressive systemic sclerosis, is associated with the production of autoantibodies specific for Scleroderma 70 antigen (topoisomerase I). Our studies show that there is an increase in the level of serum anti-topoisomerase I (topo I) autoantibodies in aged TSK mice. The monoclonal antibodies isolated from TSK mice bind to epitopes which interact with autoantibodies from scleroderma patients. A significant number of TSK monoclonal anti-topo I antibodies and serum immunoglobulin (Ig) from aged TSK mice bear a cross reactive idiotype (Id) recognized by a syngeneic monoclonal anti-Id antibody obtained from a 2 month-old TSK mouse. Analysis of V gene usage by monoclonal anti-topo I antibodies showed that the majority of these antibodies are encoded by VH genes derived from VHJ558 family pairing with VK genes from various families in a stochastic manner.

Alteration of the humoral immune response against muscle acetylcholine receptor by timed administration of alpha(1----3)dextran

Previously, we discovered a profound idiotypic connectivity among antibodies involved in the immune responses to alpha(1----3)dextran (Dex) and the acetylcholine receptor (AChR). The present studies were undertaken to assess whether these connections represent functional pathways for regulation. It was found that immunization of mice with Dex prior to challenge with AChR reduced the subsequent response to receptor. The timing of the Dex administration was crucial for this effect with a 6-day delay between Dex and AChR being optimal whereas 0- or 12-day delays proved ineffective. The suppressive effect was specific for Dex, as treatment with the closely related, but idiotypically distinct, alpha(1----6)dextran did not diminish the anti-AChR response. Consistent with functional connections in the AChR-Dex network, an inverse relationship between anti-AChR and anti-Dex antibodies was observed in these studies. Thus, high levels of anti-AChR antibodies were associated with low levels of anti-Dex antibodies and vice versa. A similar relationship was observed for serum antibodies from patients with myasthenia gravis. To investigate the mechanism for the antigen-induced cross-regulation, hybridomas were constructed from spleen cells of mice treated 6 days earlier with Dex. A variety of idiotypes (Id), anti-Id and anti-anti-Id were obtained from this fusion. In addition, sera from day-6 mice were examined for the expression of key anti-Id which might provide regulation in the anti-AChR response. The main feature of these sera was the presence of EB3-7-reactive antibodies which did not bind Dex, and hence were not identical to J558. A monoclonal antibody with similar properties was obtained from the day-6 fusion (DX6) which had additional binding specificity for anti-AChR antibodies. Antibodies induced by Dex immunization appear to participate in the cross-regulation observed here. Understanding the mechanisms involved in this phenomenon will have important implications for network theory and for prediction of immune responsiveness.

Streptococcus mutans and the problem of heart cross-reactivity

Investigations of immune responses to Streptococcus mutans have fostered consideration of vaccination as a possible preventive measure against dental caries. However, the finding that hyperimmune rabbit antisera to S. mutans sometimes give immunofluorescent reactions on human heart raised concerns over safety, especially as most individuals display circulating antibodies to this common oral organism. Recent progress in elucidating the molecular mechanisms of the well-established immunological cross-reactivity between group A streptococci and human heart tissue and the structure of S. mutans antigens permits a re-evaluation of this problem. This review examines the evidence for heart cross-reactivity induced by S. mutans in relation to studies on group A streptococci and current understanding of autoimmunity. Although the mechanisms involved in this phenomenon need further clarification, it now appears that it cannot be ascribed to antigenic similarity between heart tissue and a high-molecular-weight surface protein antigen of S. mutans.

Autoantibodies, LY-1, and immunoglobulin V gene expression in hybridomas obtained from young and from old New Zealand black mice

We obtained a large number of hybridomas from 1-month-old and 16-month-old New Zealand black mice to study the fine specificities of the autoantibodies produced, the expression of Ly-1, and the expression of the immunoglobulin V gene families in this autoimmune strain. Analysis of the autoantibody specificities yielded 2 major classifications: those specific for a single autoantigen and those that exhibited multispecific binding. Among the multispecific antibodies, 2 categories were found: an antigen-inhibitable group and an antigen-noninhibitable group. A large proportion of VHJ558 and VH7183 gene families was observed in hybridomas obtained from 1-month-old mice, and in hybridomas obtained from 16-month-old mice, there was a large proportion of VHJ558 and VH36-60 gene families. Among the autoantibody kappa chains secreted by the hybridomas, there was a higher frequency of the V kappa 1, V kappa 8, and V kappa 9 gene families. Autoantibodies were produced by both the Ly-1+ and the Ly-1- B cell subsets.

Pathogenic anti-DNA antibodies in SLE: idiotypic families and genetic origins

We have adopted an idiotypic approach to study the double stranded DNA (dsDNA) binding antibodies of systemic lupus erythematosus (SLE). Three anti-idiotypic reagents, 8.12, 3I, and F4, identify cross reactive idiotypes that are each expressed on anti-dsDNA antibodies in the sera of many patients with SLE. These idiotypic antibodies are implicated in the pathogenesis of SLE as they are present in immune complex deposits in the kidneys of patients with SLE glomerulonephritis. The autoantibody associated idiotypes are also expressed on antibodies that do not bind DNA. We are investigating the origin of the pathogenic anti-dsDNA antibodies of SLE by comparing the autoantibodies, the antibodies to foreign antigens, and the myeloma proteins that express each SLE associated idiotype. In conjunction with serological analysis of these idiotypic systems, molecular genetic studies indicate that both the 8.12 and the 3I autoantibody associated idiotypes may be germline encoded, while the F4 idiotype is generated by somatic mutation. The data further suggest that the antigenic specificity of the pathogenic anti-DNA antibodies of SLE is acquired through somatic mutation of germline immunoglobulin genes. By studying the regulation of genes capable of encoding pathogenic autoantibodies, in both SLE patients and non-autoimmune individuals, we may be able to elucidate the pathogenesis of autoimmune disease and begin to design more effective therapeutic interventions.

The LY-1 gene expression in murine hybridomas producing autoantibodies

Studies presented here demonstrate the expression of the Ly-1 gene and the detection of the Ly-1 cytodifferentiation antigen in murine hybridomas producing autoantibodies. We examined the transcription of the Ly-1 gene in thymocytes and 140 hybridomas producing autoantibodies of various specificities which were obtained from normal and autoimmune disease prone mouse strains. As previously demonstrated thymocytes stain brightly for Ly-1 by immunofluorescence and express Ly-1 transcripts. In our panel of hybridomas producing autoantibodies Ly-1 transcripts were detected in 31 (45%) out of 69 NZB hybridomas and 7 (88%) out of 8 viable motheaten hybridomas. S1 nuclease protection experiments showed that Ly-1 transcripts detected in thymocytes and B cells are the product of the same gene. The B cell transcripts are functional since immunofluorescence and Western data presented here detected the Ly-1 protein in hybridomas cells which were found to transcribe the Ly-1 gene. Interestingly a polymorphic transcription of the Ly-1 gene was observed in B cells and B cell hybridomas as compared to thymocytes. Our results obtained in the hybridoma system firmly establish a major contribution of the Ly-1 B cell subset to the production of DNA specific autoantibodies and a smaller contribution to the production of rheumatoid factors and "natural", multispecific autoantibodies.

Human polyclonal and monoclonal IgG and IgM complement 3 nephritic factors: evidence for idiotypic commonality

Complement 3 nephritic factors (C3NeF) were isolated from the sera of patients with membranoproliferative glomerulonephritis (MPGN) and the supernatants of pokeweed mitogen-stimulated mononuclear cells from patients with MPGN. Three human monoclonal C3NeF antibodies (two IgGs, CK and PH, and one IgM, K3C4) were established. Using an exhaustive series of affinity columns, we isolated anti-C3NeF idiotypic antibodies (anti-IdNeF) (three from normal and two from patient sera). Anti-IdNeF preparations bound to F(ab')2-NeF and prevented its ability to stabilize C3bBb convertase. We have used the above reagents to address questions on the genesis and the diversity of C3NeF antibodies. The following results were obtained: All anti-IdNeF preparations bound to C3NeF isolated from patient sera, cell culture supernatants, and IgG and IgM monoclonal C3NeF. None of the monoclonal C3NeF bound to an extensive battery of common antigens, including Fc portion of IgG, TNP, beta-galactosidase, DNA, and bacterial products. These data indicate that C3NeF express one common idiotype and that these antibodies are not raised in response to an obvious antigen.

B cell repertoire in adult antigen-free and conventional neonatal BALB/c mice. II. Analysis of antigen-binding capacities in relation to VH gene usage

Hybridomas were derived from lipopolysaccharide-reactive splenic B cells of adult germ-free BALB/c mice fed a chemically defined ultrafiltered "antigen-free" diet (GF-CD) and from splenic B cells of 5-day-old conventional (CV-NEO) BALB/c mice. The monoclonal antibodies (mAb) from both collections of hybridomas were tested for reactivity against a large panel of antigens of exogenous and endogenous origin. As a source of natural exogenous antigens 36 different bacteria and 9 different viruses were used, while as endogenous antigens frozen tissue sections of stomach, liver and kidney, the Hep-2 cell line and the anti-idiotopic mAb Ac38 and Ac146 were used. In both collections of mAb approximately 70% reacted with one or more bacterial antigens, while no reactivity could be detected against the viral antigens. Of the GF-CD and CV-NEO hybridomas, 16% and 19%, respectively, reacted with one or more frozen tissue sections. Overall 56% and 68% of the GF-CD and CV-NEO hybridomas, respectively, were producing multireactive antibodies reactive to several exogenous and/or endogenous antigens. Among the GF-CD hybridomas a correlation was found between multireactivity and the usage of the VH gene family PC7183. In CV-NEO hybridomas, however, the preferential utilization of the VH gene family PC7183 was found among both mono- and multireactive hybridomas. The results suggest (a) that the actual B cell repertoire of neonatal mice consists of a large proportion of multireactive B cells which are reactive with autoantigens and bacterial antigens, but not viral antigens and (b) that in antigen-deprived mice the neonatal repertoire is largely preserved during maturation of the mice.

A substantial proportion of the adult BALB/c available B cell repertoire consists of multireactive B cells

A variety of studies have documented multireactive antibodies in both the preimmune and naturally activated repertoire, but the relationship of these primarily IgM multireactive antibodies to antigen-specific primary and secondary response antibodies is currently not defined. In order to characterize the BALB/c preimmunization specificity repertoire and the baseline of naturally activated antibodies from which the immune response to a specific antigen (hen egg-white lysozyme, HEL) develops, panels of polyclonally activated blast-derived hybridomas (BlAbs) and natural antibody hybridomas (NAbs) from the spleens of unimmunized mice were screened for binding to a panel of nine complex antigens. Over half of the IgM-secreting BlAbs produced antibodies that were antigen-reactive; of these, over half were multireactive, i.e. capable of binding more than one complex antigen. There was no bias towards self vs foreign or thymus-dependent vs thymus-independent antigens. The frequency of antigen-reactive NAbs was about half the frequency of antigen-reactive antibodies found among the BlAbs. However, over half of the antigen-reactive NAbs were also multireactive, and the reactivity profile within the antigen-reactive subset of NAbs was similar to that within the antigen-reactive subset of BlAbs. These results suggest that the available repertoire of adult spleen cells contains a high proportion of multireactive antibodies, and that a subset of the available repertoire is randomly activated, yielding a small proportion of natural antibodies which closely reflect a random sampling of the available repertoire. Although monospecific precursor cells are rare, monospecific IgM BlAbs were found for all antigens in the panel except staphylococcal nuclease and mouse IgG. Monospecific as well as multireactive HEL-binding BlAbs were found at frequencies comparable to other protein antigens in the panel, and HEL-reactive NAbs were also present. On the other hand, it has previously been shown that HEL-reactive IgM antibodies (including multireactive antibodies whose specificities include HEL) are rare or absent in both the primary and secondary response to HEL. This cannot be attributed to an absence of available precursor B cells, and most likely reflects an early recruitment of HEL-reactive clones into the peripheral B cell pool. The possibility that polyreactive B cells may serve as precursors for some HEL-specific IgG antibodies is discussed.

Activation of clones producing self-reactive antibodies by foreign antigen and antiidiotype antibody carrying the internal image of the antigen

Because we found in previous work that a high fraction of antibodies exhibiting various specificities bound to glutamic acid 50-tyrosine50 homopolymer (GT) and expressed pGAT cross-reactive idiotype (IdX), we studied the activation of clones producing multireactive antibodies in 1-mo-old MRL/lpr and C3H/HeJ mice bearing VHJ haplotype. The activation of such clones was studied after mice were immunized with GT in CFA, HP20 (an anti-Id MAb carrying the internal image of GT in the D region), and a synthetic peptide corresponding to the D segment of HP20. Our results indicate that immunized mice produced both GT- and self-reactive antibodies. Study of the immunochemical properties of MAb showed that they exhibit multispecific properties and bind with similar-affinity constants to GT or self-antigens such as DNA, Smith antigen (Sm), and IgG2a. An important fraction of antibodies obtained from MRL/lpr mice immunized with HP20 expressed pGAT IdX and some of these antibodies share IdX expressed on anti-DNA, Sm, and rheumatoid factor (RFs) antibodies. The hybridomas producing multispecific autoantibodies use heavy-chain- (VH) and light-chain-variable region (VK) genes from various V gene families, suggesting that they do not derive from the pool of GAT precursors. Sequencing of VH and VK genes of two antibodies show that they can use closely related VHJ558, unmutated VK1, or different VK genes than those used by anti-GT antibodies. Our data demonstrate that clones producing antibodies binding to GT and self-antigens with similar-affinity constants can be activated by foreign or anti-Id antibodies carrying the internal image of the antigen or even by a synthetic peptide corresponding to the D segment of anti-Id antibodies.

The relationship between connectivity and tolerance as revealed by computer simulation of the immune network: some lessons for an understanding of autoimmunity

According to a classical, antigen-driven view of the immune system, autoimmunity is due to the presence of self-reactive lymphocyte clones which have not been eliminated. However, computer simulations of the immune network show that the greater the degree of connectivity of a clone, the greater its degree of tolerance to chronic antigenic stimulation. This tolerance does not correspond to an absence of response on the part of the system as a whole. On the contrary, stimulation by a 'tolerogenic antigen' results in widespread modification and overall activation of the whole network. This suggests that on an autopoietic network view of the immune system, autoimmunity arises not because of the presence of self-reactive clones, which is completely normal, but because such clones are inadequately connected to the network. This amounts to a complete reversal in perspective, whose significance for the clinical treatment of autoimmunity and the future of immunology is discussed.

Specificity of human anti-neurofilament autoantibodies

The specificities and isotypes of human antibodies that react with neurofilament (NF) proteins were examined by Western blot analysis. Two-thirds of the subjects tested had antibodies to the 200 kDa high molecular weight neurofilament protein (NF-H), and fewer had antibodies to the low and middle molecular weight neurofilament proteins (NF-L and NF-M respectively). Human autoantibodies bound to both native and dephosphorylated NF-H, but some antibodies bound to dephosphorylated NF-H only, indicating the presence of at least two target epitopes. They also recognized a fusion protein containing a segment of the NF-H protein produced by a cDNA clone in Escherichia coli, indicating that they bind to unmodified peptide epitopes. The anti-NF-H antibodies were mostly IgG, but were frequently complexed to IgA or IgM antibodies, possibly with rheumatoid factor or anti-idiotypic activity. These characteristics of anti-NF-H antibodies are most consistent with a secondary immune response that is antigen driven and T-cell dependent.

Epibodies in autoimmunity: antisera against autoantibodies to the renal glomerular basement membrane react with idiotypes as well as with autoantigens

The results reported here show that we have experimentally produced xenogeneic anti-idiotypic antibodies to rat autoantibodies specific for the renal GBM and one of its components, laminin. Cross-reactive idiotypes have been detected by anti-idiotypic antibodies (anti-Id) on autoantibodies to the GBM (anti-GBM) from rats of different strains, confirming the results obtained in other autoantibody systems. During the course of studies aimed at determining whether anti-Id were directed to the paratope of anti-GBM antibodies, we have observed the presence of anti-GBM (and anti-laminin) antibodies in rabbit sera with anti-Id. Affinity chromatography experiments suggest that anti-GBM reactions detected with our anti-Id sera may be caused by a heterogeneous combination of anti-Id. Thus, Ab2 alpha (and/or Ab2 gamma, all reacting with Ab1), Ab2 epsilon (epibodies, that bind to both Ab1 and GBM) and Ab3 (similar to Ab1 and therefore, reacting with GBM) may be present in our anti-Id sera. It has been suggested that antibodies displaying epibody properties may be involved in the mutual regulation of autoreactive clones and represent an important component of the autoimmune process.

Pathogenic subsets of antibodies to DNA

Among the autoantibodies that are known to play a role in the pathogenesis of autoimmune diseases, antibodies to DNA (anti-DNA) have been the subject of much study. Several interesting observations have resulted. The ability to make antibodies that bind DNA is not abnormal. Normal mice and humans can produce antibodies that bind DNA. On the other hand, large quantities of antibodies to DNA are found in the sera of patients with systemic lupus erythematosus (SLE), and complement-fixing antibodies to double-stranded (ds) DNA cause some of the tissue lesions, especially glomerulonephritis (GN). Why, then, do some individuals make anti-DNA that deposits in glomeruli, skin, and other tissue, resulting in organ damage? It is likely that disease results from a combination of several factors--ability to make pathogenic antibody subsets, inability to downregulate those subsets, and "tissue susceptibility" to injury from those antibodies and their immune complexes. This chapter will focus on the characteristics of pathogenic antibody subsets and their regulation.

Quantitation of autoantibody-secreting B cells in systemic lupus erythematosus

An ELISA spot assay was used to quantitate the number of autoantibody-secreting B cells in the peripheral blood of patients with systemic lupus erythematosus. Patients with active disease had 20 fold more anti-DNA, 4 fold more anti-actin and 3 fold more anti-myosin secreting lymphocytes than controls but normal numbers of anti-cardiolipin and anti-transferrin secreting B cells. 60% of SLE patients had increased numbers of B cells reactive with multiple autoantigens. These data suggest that B cell activation in SLE may be influenced by both antigen-specific and antigen-independent factors.

Natural murine autoantibodies and conventional antibodies exhibit similar degrees of antigenic cross-reactivity

Splenic B cells from normal and autoimmune mice were transferred to MHC-compatible xid recipients. Monoclonal antibodies were secreted by the transferred B cells in splenic fragment cultures. These antibodies were evaluated for reactivity and cross-reactivity against a panel of six autoantigens and two conventional antigens using an ELISA assay. The autoantibodies and conventional antibodies produced in splenic fragment cultures by normal DBA/2 and autoimmune NZB B cells expressed similar degrees of antigenic cross-reactivity. Previous studies have demonstrated that ELISA assays of splenic fragment culture supernatants detect antibodies with affinities of 5 x 10(6) M-1 or greater. We therefore also analyzed the cross-reactivity of monoclonal antibodies derived from hybridomas. This permitted an assessment of antibodies with lower binding affinities. Cross-reactivity was detected more frequently among these hybridomas. Consistent with our earlier observations, hybridoma antibodies specific for conventional antigens exhibited cross-reactivity with a frequency similar to that of antibodies specific for autoantigens.