Variable region gene selection of immunoglobulin G-expressing B cells with specificity for a defined epitope on type II collagen

Antigen-presenting autoreactive B cells activate regulatory T cells and suppress autoimmune arthritis in mice

B cells undergo several rounds of selection to eliminate potentially pathogenic autoreactive clones, but in contrast to T cells, evidence of positive selection of autoreactive B cells remains moot. Using unique tetramers, we traced natural autoreactive B cells (C1-B) specific for a defined triple-helical epitope on collagen type-II (COL2), constituting a sizeable fraction of the physiological B cell repertoire in mice, rats, and humans. Adoptive transfer of C1-B suppressed arthritis independently of IL10, separating them from IL10-secreting regulatory B cells. Single-cell sequencing revealed an antigen processing and presentation signature, including induced expression of CD72 and CCR7 as surface markers. C1-B presented COL2 to T cells and induced the expansion of regulatory T cells in a contact-dependent manner. CD72 blockade impeded this effect suggesting a new downstream suppressor mechanism that regulates antigen-specific T cell tolerization. Thus, our results indicate that autoreactive antigen-specific naïve B cells tolerize infiltrating T cells against self-antigens to impede the development of tissue-specific autoimmune inflammation.

The structure, specificity and function of anti-citrullinated protein antibodies

In this Perspectives article, we outline a proposed model for understanding the specificity and function of anti-citrullinated protein antibodies (ACPAs). We suggest that ACPAs vary in specificity between two extremes: some are 'promiscuous' in that they are highly specific for the citrulline side chain, but cross-react with a range of citrullinated peptides, whereas others are 'private' in that their recognition of citrulline as well as proximal amino acid side chains enables protein-specific interactions. Promiscuous ACPAs tend to dominate in the sera both before and after the onset of rheumatoid arthritis, but their functional role has not been clarified. No firm evidence exists that these ACPAs are pathogenic. By contrast, private ACPAs encompass antibodies that specifically recognize citrullinated epitopes on joint proteins or that cross-react with joint proteins, thereby opening up the possibility that these private ACPAs are arthritogenic. These joint-reactive antibodies are more likely to target joints by binding to joint tissues and to promote the formation of local immune complexes leading to bone erosions, pain and arthritis.

Streptococcal Endo-β-N-Acetylglucosaminidase Suppresses Antibody-Mediated Inflammation In Vivo

Endo-β-N-acetylglucosaminidase (EndoS) is a family 18 glycosyl hydrolase secreted by Streptococcus pyogenes. Recombinant EndoS hydrolyzes the β-1,4-di-N-acetylchitobiose core of the N-linked complex type glycan on the asparagine 297 of the γ-chains of IgG. Here, we report that EndoS and IgG hydrolyzed by EndoS induced suppression of local immune complex (IC)-mediated arthritis. A small amount (1 µg given i.v. to a mouse) of EndoS was sufficient to inhibit IgG-mediated arthritis in mice. The presence of EndoS disturbed larger IC lattice formation both in vitro and in vivo, as visualized with anti-C3b staining. Neither complement binding in vitro nor antigen-antibody binding per se were affected. Thus, EndoS could potentially be used for treating patients with IC-mediated pathology.

Targeting IgG in Arthritis: Disease Pathways and Therapeutic Avenues

Rheumatoid arthritis (RA) is a polygenic and multifactorial syndrome. Many complex immunological and genetic interactions are involved in the final outcome of the clinical disease. Autoantibodies (rheumatoid factors, anti-citrullinated peptide/protein antibodies) are present in RA patients' sera for a long time before the onset of clinical disease. Prior to arthritis onset, in the autoantibody response, epitope spreading, avidity maturation, and changes towards a pro-inflammatory Fc glycosylation phenotype occurs. Genetic association of epitope specific autoantibody responses and the induction of inflammation dependent and independent changes in the cartilage by pathogenic autoantibodies emphasize the crucial contribution of antibody-initiated inflammation in RA development. Targeting IgG by glyco-engineering, bacterial enzymes to specifically cleave IgG/alter N-linked Fc-glycans at Asn 297 or blocking the downstream effector pathways offers new avenues to develop novel therapeutics for arthritis treatment.

A murine Ig light chain transgene reveals IGKV3 gene contributions to anti-collagen types IV and II specificities

A subset of autoimmune diseases result from autoantibodies targeting epitopes on matrix collagen. The most extensively studied are anti-glomerular basement membrane glomerulonephritis (or its systemic counterpart Goodpasture's disease) that destroys kidneys and lungs, and rheumatoid arthritis that leads to disabling arthritis. Autoantibodies in these disorders bind evolutionarily conserved conformational epitopes on the noncollagenous domain 1 (NC1) of the alpha3 chain of type IV [alpha3(IV)NC1] collagen in glomerular and alveolar basement membranes, and on native or citrullinated type II collagen (CII) in joint cartilage, respectively. The genetic origins of pathogenic anti-collagen B cells in these diseases is unknown, but observations from murine models raise the possibility that they overlap despite distinct in vivo immunopathologies. Monoclonal autoantibodies isolated from mice immunized with alpha3(IV)NC1 collagen or CII show a biased use of Ig light chains (LC) encoded by genes of the IGKV3 subgroup (previously Vk21 family), paired with diverse Ig heavy chains. To further explore this relationship and determine if a single murine IGKV3 LC independently predisposes to both anti-collagen responses, we generated a novel transgenic (Tg) C57BL/6 mouse that expresses a productively rearranged IGKV3-encoded LC, termed mLCV3-Tg, in conjunction with endogenously rearranged Ig heavy chains. Tg mice are also genetically deficient in endogenous kappa chains to permit tracking of the mLCV3 transgene. We show that mLCV3-Tg mice are susceptible to humoral autoimmunity against both collagen chains. Anti-alpha3(IV)NC1 collagen, but not anti-CII, mLCV3-encoded Ig are detected in serum of unmanipulated Tg mice, while Toll-like receptor ligands induce secretion of mLCV3-Tg autoantibodies of both collagen specificities from splenocytes ex vivo. This indicates developmental survival of mLCV3-Tg B cells reactive with each antigen, and is consistent with production of the two anti-collagen autoIg from distinct B cell populations. Reduced B cell numbers, low serum Ig kappa levels, low cell surface Ig kappa density, and abundant endogenous lambda chain expression suggest that subsets of IGKV3-encoded B cells are regulated in vivo by mechanisms that include deletion, anergy, and LC editing. These results support the notion that murine IGKV3 LCs contribute structural fitness to antigen binding sites that support diverse anti-collagen autoimmune responses, that these responses are regulated in vivo, and that these cells can nonetheless readily escape immune regulation.

Autoimmune priming, tissue attack and chronic inflammation - the three stages of rheumatoid arthritis

Extensive genome-wide association studies have recently shed some light on the causes of chronic autoimmune diseases and have confirmed a central role of the adaptive immune system. Moreover, better diagnostics using disease-associated autoantibodies have been developed, and treatment has improved through the development of biologicals with precise molecular targets. Here, we use rheumatoid arthritis (RA) as a prototype for chronic autoimmune disease to propose that the pathogenesis of autoimmune diseases could be divided into three discrete stages. First, yet unknown environmental challenges seem to activate innate immunity thereby providing an adjuvant signal for the induction of adaptive immune responses that lead to the production of autoantibodies and determine the subsequent disease development. Second, a joint-specific inflammatory reaction occurs. This inflammatory reaction might be clinically diagnosed as the earliest signs of the disease. Third, inflammation is converted to a chronic process leading to tissue destruction and remodeling. In this review, we discuss the stages involved in RA pathogenesis and the experimental approaches, mainly involving animal models that can be used to investigate each disease stage. Although we focus on RA, it is possible that a similar stepwise development of disease also occurs in other chronic autoimmune settings such as multiple sclerosis (MS), type 1 diabetes, and systemic lupus erythematosus.

Chemical cross-linking abrogates adjuvant potential of natural polymers

Natural polymers like chitosan and alginic acid are extensively used in biomedicine for different applications.

Characterization of chemically defined poly-N-isopropylacrylamide based copolymeric adjuvants

PNiPAAm is a thermo-responsive polymer with an adjuvant activity. To identify the minimal chemical structure present within PNiPAAm responsible for its adjuvant property, three different constituent polymers with specific functional groups were synthesized through free radical reaction and tested their adjuvant potential along with PNiPAAm. Among them, polymer with isopropyl attached to an amide showed maximal adjuvant activity in rodents followed by polymer with amide or ketone functional groups. However, secondary amine containing polymer did not show any adjuvant activity. In addition, to improve the adjuvant properties of PNiPAAm, we incorporated an affinity ligand, boronate. At first, we synthesized and characterized the dual responsive copolymers PNiPAAm-co-VPBA and PNiPAAm-co-VPBA-co-DMAEMA. Biocompatibility of these copolymers was confirmed both in vitro and in vivo. Mice injected with these copolymers mixed with collagen (CII) developed significant levels of anti-CII antibodies comprising of all the major IgG subclasses and an increased T cell activation. At the injection site, massive infiltration of immune cells was observed. However, only PNiPAAm-co-VPBA-co-DMAEMA-CII induced arthritis in mice after injection of 0.5M fructose confirming the importance of effective release of CII from the polymer for its adjuvant activity. Thus, a fine balance of hydrophobicity and hydrophilicity promotes adjuvant properties and continuous release of antigen, in this case CII, from polymer is essential for its adjuvant activity.

Adjuvant properties of a biocompatible thermo-responsive polymer of N-isopropylacrylamide in autoimmunity and arthritis

To evaluate the thermo-responsive poly(N-isopropylacrylamide) (PNiPAAm) polymer as an adjuvant, we synthesized PNiPAAm through free radical polymerization and characterized it both in vitro and in vivo. The polymer when mixed with collagen type II (CII) induced antigen-specific autoimmunity and arthritis. Mice immunized with PNiPAAm-CII developed significant levels of CII-specific IgG response comprising major IgG subclasses. Antigen-specific cellular recall response was also enhanced in these mice, while negligible level of IFN-γ was detected in splenocyte cultures, in vitro. PNiPAAm-CII-immunized arthritic mouse paws showed massive infiltration of immune cells and extensive damage to cartilage and bone. As determined by immunostaining, most of the CII protein retained its native configuration after injecting it with PNiPAAm in naive mice. Physical adsorption of CII and the high-molecular-weight form of moderately hydrophobic PNiPAAm induced a significant anti-CII antibody response. Similar to CII, mice immunized with PNiPAAm and ovalbumin (PNiPAAm-Ova) induced significant anti-ovalbumin antibody response. Comparable levels of serum IFN-γ, IL-1β and IL-17 were observed in ovalbumin-immunized mice with complete Freund, incomplete Freund (CFA and IFA) or PNiPAAm adjuvants. However, serum IL-4 levels were significantly higher in PNiPAAm-Ova and CFA-Ova groups compared with the IFA-Ova group. Thus, we show for the first time, biocompatible and biodegradable thermo-responsive PNiPAAm can be used as an adjuvant in several immunological applications as well as in better understanding of the autoimmune responses against self-proteins.

Collagen type II is recognized by a pathogenic antibody through germline encoded structures

Collagen type II (CII) is a cartilage-specific target of pathologic humoral autoimmune responses in rheumatoid arthritis as well as in the collagen-induced arthritis model. The aim of the present study is to investigate the critical amino acid residues conferring CII epitope specificity of the prototypic arthritogenic murine mAb CIIC1. A homology model of the CIIC1 single-chain antibody fragment (CIIC1scFv) in complex with its triple helical epitope was established. In silico predictions based on extensive molecular dynamics simulations were experimentally tested by the recombinant expression and functional analysis of CIIC1scFv containing alanine replacements allowing the identification of crucial CII-binding sites in the CDR2 and CDR3 regions of both heavy and light chains. Since the conversion of the CIIC1scFv sequence into the respective germline at all 13 somatically mutated positions did not affect its CII binding, our data indicate that potentially harmful cartilage-specific humoral autoimmunity could be germline encoded. The molecular modeling further demonstrates that the rigid collagen triple helix restricts the likelihood of molecular interactions with the CDR regions of the antibody considerably compared with globular antigens. These sterical constraints provide an explanation as to why somatic mutations in the arthritogenic autoantibody have no obvious impact on CII recognition.

Antibody-induced arthritis: disease mechanisms and genes involved at the effector phase of arthritis

During the development of rheumatoid arthritis (RA) autoantibodies to IgG-Fc, citrullinated proteins, collagen type II (CII), glucose 6 phosphoisomerase (G6PI) and some other self-antigens appear. Of these, a pathogenic effect of the anti-CII and anti-G6PI antibodies is well demonstrated using animal models. These new antibody mediated arthritis models have proven to be very useful for studies involved in understanding the molecular pathways of the induction of arthritis in joints. Both the complement and FcgammaR systems have been found to play essential roles. Neutrophils and macrophages are important inflammatory cells and the secretion of tumour necrosis factor-alpha and IL-1beta is pathogenic. The identification of the genetic polymorphisms predisposing to arthritis is important for understanding the complexity of arthritis. Disease mechanisms and gene regions studied using the two antibody-induced arthritis mouse models (collagen antibody-induced arthritis and serum transfer-induced arthritis) are compared and discussed for their relevance in RA pathogenesis.

Collagen antibody induced arthritis

Rheumatoid arthritis (RA) is a polygenic and multifactorial disease. Many complex immunological and genetic interactions are involved in the final out come of the clinical disease. To understand the various disease pathways operating during the disease course, we need many different animal models. Collagen induced arthritis (CIA) is one of the widely used animal models sharing many pathological and histological similarities with RA and antibodies play an important role in the inflammatory phase of CIA. This chapter describes, in detail, an animal model for arthritis using CII specific monoclonal antibodies, the so-called collagen antibody induced arthritis (CAIA), which shares many characteristics of CIA. CAIA model provides an opportunity to study the inflammatory phase of arthritis without involving the priming phase of the immune response. CAIA can be used for not only studying inflammatory processes in arthritis and screening drug candidates controlling joint inflammatory phase but also as a model for studying common mechanisms involved in many antibody mediated diseases.

Chronic development of collagen-induced arthritis is associated with arthritogenic antibodies against specific epitopes on type II collagen

Antibodies against type II collagen (CII) are important in the development of collagen-induced arthritis (CIA) and possibly also in rheumatoid arthritis. We have determined the fine specificity and arthritogenicity of the antibody response to CII in chronic relapsing variants of CIA. Immunization with rat CII in B10.Q or B10.Q(BALB/c×B10.Q)F₂ mice induces a chronic relapsing CIA. The antibody response to CII was determined by using triple-helical peptides of the major B cell epitopes. Each individual mouse had a unique epitope-specific response and this epitope predominance shifted distinctly during the course of the disease. In the B10.Q mice the antibodies specific for C1 and U1, and in the B10.Q(BALB/c×B10.Q)F₂ mice the antibodies specific for C1, U1 and J1, correlated with the development of chronic arthritis. Injection of monoclonal antibodies against these epitopes induced relapses in chronic arthritic mice. The development of chronic relapsing arthritis, initially induced by CII immunization, is associated with an arthritogenic antibody response to certain CII epitopes.

Molecular analysis of monoclonal antibodies to group variant capsular polysaccharide of Neisseria meningitidis: recurrent heavy chains and alternative light chain partners

We determined the molecular sequence of monoclonal antibodies (mAbs) to serogroups B and C capsular polysaccharides (PS) of Neisseria meningitidis. N. meningitidis infections are a leading cause of bacterial septicemia and meningitis in humans. Antibodies to PS are fundamental to host defense and diagnostics. The polysaccharide capsule of group B N. meningitidis is poorly immunogenic and thus is an important model for studying pathogen-host co-evolution through understanding the molecular basis of the host immune response. We used a modified reverse-transcriptase PCR to amplify and sequence the V-genes of murine hybridomas produced against types B and C capsular PS. Databank analysis of the sequences encoding the V-genes of type C capsular PS mAb, 4-2-C, reveal that heavy chain alleles are recurrently used to encode this specificity in mice. Interestingly, a V-gene from the same germline family also encodes the V-domain of mAbs 2-2-B, which targets the antigenically distinct serogroup B capsular PS. Somatic mutation, junctional diversity and alternative light chains collectively impart the specificity for these serologically distinct epitopes. Knowledge of the specific immunoglobulin genes used to target common bacterial virulence factors may lead to insights on pathogen-host co-evolution, and the potential use of this information in pre-symptomatic diagnosis is discussed.

Phage display for epitope determination: a paradigm for identifying receptor-ligand interactions

Antibodies that react with many different molecular species of protein and non-protein nature are widely studied in biology and have particular utilities, but the precise epitopes recognized are seldom well defined. The definition of epitopes by X-ray crystallography of the antigen-antibody complex, the gold standard procedure, has shown that most antibody epitopes are conformational and specified by interactions with topographic determinants on the surface of the antigenic molecule. Techniques available for the definition of such epitopes are limited. Phage display using either gene-specific libraries, or random peptide libraries, provides a powerful technique for an approach to epitope identification. The technique can identify amino acids on protein antigens that are critical for antibody binding and, further, the isolation of peptide motifs that are both structural and functional mimotopes of both protein and non-protein antigens. This review discusses techniques used to isolate such mimotopes, to confirm their specificity, and to characterize peptide epitopes. Moreover there are direct practical applications to deriving epitopes or mimotopes by sequence, notably the development of new diagnostic reagents, or therapeutic agonist or antagonist molecules. The techniques developed for mapping of antibody epitopes are applicable to probing the origins of autoimmune diseases and certain cancers by identifying "immunofootprints" of unknown initiating agents, as we discuss herein, and are directly applicable to examination of a wider range of receptor-ligand interactions.

Identification of conformation-dependent epitopes and V gene selection in the B cell response to type II collagen in the DA rat

Collagen-induced arthritis (CIA) is a widely used model for rheumatoid arthritis. Induction of CIA in rats using rat type II collagen (CII) results in a chronic arthritis in which anti-CII antibodies are believed to play a pathogenic role. In this study, we analyzed the epitope selection and V gene usage in the anti-CII response in the DA rat. A panel of CII-reactive B cell hybridomas was established from the draining lymph nodes 11 days after immunization. All of the CII-specific antibodies bound cartilage in vivo, showing that these are true autoantibodies. These antibodies were all IgG and specific for several distinct triple helical epitopes on CII. Interestingly, the major epitope, recognized by four different antibodies, was identical with the major B cell epitope in the mouse CII located at position 359--369 (denoted as C1(III)). The Q52 and PC7183 V(H) gene families encoded 12 out of 14 sequenced heavy chains. There was a relatively more heterogeneous usage of V(L) genes as the antibodies were encoded by four different V(kappa) families (V(kappa)1, V(kappa)2, V(kappa)12/13 and V(kappa)RF). As in the mouse, some of the V genes used showed germline characteristics. We conclude that the immune response in the rat shares epitope specificity and a constrained V gene repertoire with the mouse. However, the V genes used for recognition of the closely related collagen structures differed considerably between mouse and rat, indicating an influence of the species-specific variation in the V gene repertoire.

Phagotopes derived by antibody screening of phage-displayed random peptide libraries vary in immunoreactivity: studies using an exemplary monoclonal antibody, CII-C1, to type II collagen

Antibody screening of phage-displayed random peptide libraries to identify mimotopes of conformational epitopes is promising. However, because interpretations can be difficult, an exemplary system has been used in the present study to investigate whether variation in the peptide sequences of selected phagotopes corresponded with variation in immunoreactivity. The phagotopes, derived using a well-characterized monoclonal antibody, CII-C1, to a known conformational epitope on type II collagen, C1, were tested by direct and inhibition ELISA for reactivity with CII-C1. A multiple sequence alignment algorithm, PILEUP, was used to sort the peptides expressed by the phagotopes into clusters. A model was prepared of the C1 epitope on type II collagen. The 12 selected phagotopes reacted with CII-C1 by both direct ELISA (titres from < 100-11 200) and inhibition ELISA (20-100% inhibition); the reactivity varied according to the peptide sequence and assay format. The differences in reactivity between the phagotopes were mostly in accord with the alignment, by PILEUP, of the peptide sequences. The finding that the phagotopes functionally mimicked the C1 epitope on collagen was validated in that amino acids RRL at the amino terminal of many of the peptides were topographically demonstrable on the model of the C1 epitope. Notably, one phagotope that expressed the widely divergent peptide C-IAPKRHNSA-C also mimicked the C1 epitope, as judged by reactivity in each of the assays used: these included cross-inhibition of CII-C1 reactivity with each of the other phagotopes and inhibition by a synthetic peptide corresponding to that expressed by the most frequently selected phagotope, RRLPFGSQM. Thus, it has been demonstrated that multiple phage-displayed peptides can mimic the same epitope and that observed immunoreactivity of selected phagotopes with the selecting mAb can depend on the primary sequence of the expressed peptide and also on the assay format used.

Arthritis-related B cell epitopes in collagen II are conformation-dependent and sterically privileged in accessible sites of cartilage collagen fibrils

In collagen-induced arthritis, a murine autoimmune model for rheumatoid arthritis, immunization with native but not heat-denatured cartilage-specific collagen type II (CII) induces a B cell response that largely contributes to arthritogenicity. Previously, we have shown that monoclonal antibodies established from arthritis prone DBA/1 mice require the triple-helical conformation of their epitopes for antigen recognition. Here, we present a novel approach to characterize arthritis-related conformational epitopes by preparing a panel of 130 chimeric collagen X/CII molecules. The insertion of a series of CII cassettes into the triple-helical recombinant collagen X allowed for the first time the identification of five triple-helical immunodominant domains of 5-11 amino acid length, to which 75% of 36 monoclonal antibodies bound. A consensus motif, "R G hydrophobic," was found in all immunodominant epitopes. The antibodies were encoded by a certain combination of V-genes in germline configuration, indicating a role of the consensus motif in V-gene selection. The immunodominant domains are spread over the entire monomeric CII molecule with no apparent order; however, a highly organized arrangement became apparent when the CII molecules were displayed in the quarter-staggered assembly within a fibril. This discrete epitope organization most likely reflects structural constraints that restrict the exposure of CII epitopes on the surface of heterotypically assembled cartilage fibrils. Thus, our data suggest a preimmune B cell selection process that is biased by the accessibility of CII determinants in the intact cartilage tissue.

Therapeutic effects of estradiol benzoate on development of collagen-induced arthritis (CIA) in the Lewis rat are mediated via suppression of the humoral response against denatured collagen type II (CII)

The effects of estradiol benzoate (EB) on the development of anti-CII antibodies and their pathogenic potential were studied during the progress of established CIA in the rat. CIA was induced in mature female Lewis rats by two subcutaneous inoculations containing bovine native CII (BCIIn), emulsified in Freund's incomplete adjuvant. Clinical arthritis fully developed by day 18 and then EB (1 mg/kg body wt per day, diluted in corn oil (CO)) was administered intramuscularly every second day thereafter. Antibodies binding four different CIIs (bovine or rat, either native or heat-denatured) were detected in sera and joint tissue extracts by means of solid-phase ELISA. Pharmacological doses of EB (>0.2 mg/kg body wt per day) caused significant remission of established CIA 5-7 days after treatment, and selectively suppressed the production of antibodies specific for denatured CII. To evaluate the arthritogenic potential of circulating anti-CIId IgG, transfer experiments were performed. IgG anti-CIIn, purified from EB-treated CIA rats, was not arthritogenic, whereas IgG anti-denatured (CIId), purified from CO-treated CIA rats, caused severe passive arthritis. Furthermore, pretreatment with rat CIId protected against subsequent induction of CIA, and this protection was associated with suppressed antibody production against CIId. Collectively, our results indicate that antibodies specific for CIId are involved in the pathogenesis of CIA, and that oestrogen-related remission of clinical arthritis may by caused by a selective suppression of antibodies produced against degraded/denatured CII.

Binding of autoreactive mouse anti-type II collagen antibodies derived from the primary and the secondary immune response investigated with the biosensor technique

The reactivity of autoantibodies to type II collagen, secreted by B cells isolated from the primary and the secondary immune response to rat type II collagen in DBA/1 mice, was investigated using BIAcore 2000 instrumentation. Assays were performed on both collagen and antibody surfaces. These assays demonstrated a 100-fold difference in affinity between primary and secondary immune response antibodies. The difference in affinity was almost entirely due to differences in the dissociation rate constant. Somatic mutations in secondary clones were in one case associated with a 3-4-fold difference in affinity and in another case appeared to be without any effect on the binding activity.

VH gene structure predicts a large potential anti-insulin repertoire

The majority of insulin antibodies derived from immunization are IgG antibodies that cross-react extensively with the autologous hormone. To examine the relationship between VH genes expressed by such self-reactive antibodies and their germline (non-rearranged) counterparts, we used the polymerase chain reaction (PCR) to amplify and isolate the germline progenitors of anti-insulin VH genes derived from BALB/c mice immunized with beef or human insulin. Results indicate that two anti-insulin mAbs (123 and 124) express VH genes which arise from a small subset of the J558 gene family and are highly homologous to the VH gene used by the murine CD5 + B-cell tumor, BCL1. The anti-insulin IgG mAb 127 belongs to the VH-VIII (Vgam 3.2) family and the amplification and isolation of germline VH genes from this small family precisely identified only two somatic mutation events in the CDRH2 of mAb 127. Another anti-insulin mAb, 133, also shows two replacement substitutions in the CDRHs when compared to the germline encoded anti-dextran antibody 19.1.2. These findings indicate that the IgG response to this small self-protein uses multiple VH genes which are largely germline encoded with only a low level of somatic mutation in their CDRHs. Additionally, analysis of N-segment additions in CDRH3s indicates anti-insulin B cells may originate from both early (fetal) and adult repertoires. These data are consistent with the concept that the mechanisms of clonal anergy or deletion do not regulate anti-insulin B cells and indicate that there is a large potential VH gene repertoire for insulin.

Molecular characterization of J558 genes encoding tight-skin mouse autoantibodies: identical heavy-chain variable genes code for antibodies with different specificities

Tight-skin mouse, a mutant strain with a single gene defect, develops cutaneous hyperplasia and specific autoantibodies, like humans affected by scleroderma. The autoantibodies produced in the tight-skin mouse are encoded primarily by heavy-chain variable (VH) genes from the J558 family. To understand the genetic basis of production of autoantibodies, we have analyzed the structure of J558 genes encoding these autoantibodies. The results showed that J558 genes encoding these antibodies were not derived from a selected germ-line gene(s) or a single subfamily but were derived from genes belonging to diverse J558 subfamilies. However, two prototype VH genes representing two new subfamilies were found to be repeatedly expressed in their germ-line form in eight independent clones. Autoantibodies with distinct specificities appear to be generated by pairing of similar/identical VH genes with different V kappa genes derived from the same or different families. Fourteen of 18 autoantibodies shared a conserved heptapeptide sequence motif, YNEKFKG, in the second complementarity-determining region of heavy chains. Usage of germ-line genes from diverse J558 subfamilies bearing a common motif to encode autoantibodies suggests a regulatory role for this motif. Thus, selection and expansion of the autoreactive B-cell repertoire in the tight-skin mouse appear to be VH-gene mediated. The frequency of N nucleotide addition at diversity-joining (D-JH) junctions was lower, whereas the frequency of usage of the DFL16 segment was higher. Finally, in contrast to normal and other autoimmune mouse strains, the frequencies of D-D fusions and D inversions were higher in tight-skin mouse total immunoglobulin as well as autoantibody repertoires.

Molecular and structural analysis of nuclear localizing anti-DNA lupus antibodies

To determine the structure of three nuclear localizing lupus anti-DNA immunoglobulins (Igs) and to search for clues to mechanisms of cellular and/or nuclear access, their H- and L-chain variable region sequences were determined and subjected to three-dimensional modeling. Although the results indicate heterogeneity in their primary structures, the H chains are encoded by 3 members of the J558 VH gene family with a common tertiary conformation that is not shared by a J558-encoded nonnuclear localizing anti-DNA control Ig. Furthermore, at least two of the Igs share a conformational motif in the H-chain CDR3, and all three Igs contain multiple positively charged amino acids in their CDRs, resembling nuclear localization signals that direct protein nuclear import. Notably, each VH and VK gene is also found recurrently among previously described autoantibodies. Molecular analysis further indicates that both germline-encoded and significantly mutated V genes can generate nuclear localizing anti-DNA Ig.

Germline-encoded IgG antibodies bind mouse cartilage in vivo: epitope- and idiotype-specific binding and inhibition

Autoantibodies specific for type-II collagen (CII) occur in mice and rats with collagen-induced arthritis (CIA). The binding in vitro and in vivo of mouse monoclonal antibodies (MoAbs) specific for separate epitopes in CII have been investigated. Two-day-old mice were injected intraperitoneally (i.p.) with the anti-CII antibody CIID3 in both unlabelled and biotinylated form. It was found that antibodies binding to the same epitope in CII in vivo can inhibit others from binding in an epitope-specific fashion. The binding in vivo and in vitro of anti-CII antibodies could be inhibited also by an anti-idiotypic rat antiserum produced against the D3 antibody. The anti-idiotypic antiserum inhibited the binding of the antibody D3 and the idiotypically related antibody C2. The cDNA's of anti-CII antibodies D3, C2, and F4 were sequenced and found to contain germline encoded V-genes, apparently without somatic mutations. The variable heavy chain of D3 and C2 both expressed the same VH rearrangement, confirming that they share idiotypes. This report demonstrates that CII-specific germline-encoded IgG autoantibodies bind specifically to normal cartilage in vivo via their combining site.