Public and individual idiotopes in the anti-poly(Glu60, Ala30, Tyr10) response: analysis by monoclonal antibodies

Generalization of single immunological experiences by idiotypically mediated clonal connections

Clonal interactions of B cells by idiotope-specific mutual recognition of their antigen receptors with the participation of T cells were assumed to form a web of unknown density, referred to as the idiotypic network. Although these clonal connections were proposed to fulfill important internal regulatory functions, their biological significance, especially in relation to antigen-induced immune responses, remained a mystery. In view of this, we postulate that the basic function of the idiotypic internal connection between B and T cell antigen receptors is to transform antigen-induced cellular activations, by idiotypic crossreactivity, into the regulation of cell clones with different antigen specificities. This process leads not only to the suppression of major clones but also to the activation of minor ones. The latter activating property may allow the generalization of single antigenic experiences, so that the immune system in its entirety benefits in its battle against environmental microbes. Such idiotypic clonal interactions are particularly effective in early ontogeny. During a short neonatal imprinting period, maternal immunological knowledge in the form of somatically mutated, high-affinity IgG antibodies, acquired through a continuous encounter with external antigens, guides the initial ontogenetic development of the immune system and so exerts long-lasting transgenerational advantageous effects in the offspring.

V lambda-light chain genes reconstitute immune responses to defined carbohydrate antigens or haptens by utilizing different VH genes

The contribution of the lambda-light chain to the development of peripheral B cell repertoire and generation of specific antibodies to haptens and polysaccharide antigens was studied in genetically manipulated kappa-deficient and lambda 2-transgenic mice. The results clearly demonstrate a non-stoichiometric VH gene family expression in the absence of k-light chain and suggest a non-stochastic pairing between VH and V lambda genes, expressed in the peripheral B cell repertoire. A shift in VH gene utilization in the case of VI lambda + antibodies was evident in response to beta 2-6 fructosan and TNP hapten. These observations demonstrate the availability of compensatory mechanisms in the absence of VK genes and are consistent with the hypothesis that VH gene family expression is controlled by genetic factors from inside the VH locus. Furthermore, genetic factors from outside the VH locus, namely restricted available light chain diversity, may lead to a shift in VH gene utilization in the peripheral B cell repertoire.

Antibody response against poly (Glu60Ala30Tyr10) terpolymer and bacterial levan in kappa-deficient mice

In murine species, the kappa (+)-bearing immunoglobulins dominate the antibody (Ab) repertoire with a kappa/lambda ratio of 95:5. The aim of the present study is to investigate the characteristics of the antibody response in kappa-deficient (K-/-) mice immunized with a T-dependent synthetic antigen, poly(Glu60Ala30Tyr10) (GAT) and a T-independent antigen, bacterial levan (BL). K-/- mice were obtained by targeted deletion of the J kappa C kappa gene segments. In response to GAT, K-/- mice respond by producing increasing amounts of anti-GAT Ig lambda 1 and Ig lambda 2 in the primary as well as secondary response, although anti-GAT specific monoclonal antibodies (mAb) raised in K-/- mice are mostly of IgM isotype. The GAT public idiotype, GATIdX, present on all GAT-specific Ab bearing kappa light chain, is not detected in the sera of K-/- mice or on any of the anti-GAT lambda 1 mAb. In response to BL, the amount of Ig lambda 1+ Ab in K-/- mice is comparable to the amount of Ig kappa + Ab in normal mice. However, lambda 2+ Ab are detected neither in wild-type nor in K-/- mice. Like kappa + Ab, the majority of lambda 1+ mAb are specific for beta 2-6 fructosan present in BL and rye levan and, to some extent, express the BL-specific idiotype, A48ld. Our results show that important compensatory mechanisms occur in kappa-deficient mice, restoring their ability to mount immune responses against a variety of T-dependent and T-independent antigens by the alternative usage of the clonally restricted lambda repertoire.

Poly(Glu60Ala30Tyr10) (GAT)-induced IgG monoclonal antibodies cross-react with various self and non-self antigens through the complementarity determining regions. Comparison with IgM monoclonal polyreactive natural antibodies

Previous studies have shown that the antibodies of the preimmune repertoire are able to bind to various auto- and xenoantigens including chemical haptens. Sequence analysis of two such murine monoclonal IgM natural autoantibodies showed that they are encoded by unmutated germ-line variable regions of the light and heavy chain (V alpha and VH) genes which were also found in various murine immune responses, like phenyl-oxazolone, dinitrophenyl, arsonate, phosphorylcholine and influenza virus hemagglutinin. These data raised the question as to whether induced antibodies possessing germ-line sequence are also able to react with autoantigens. To study this problem, anti-poly(Glu60Ala30Tyr10) (GAT) and anti-alprenolol (Alp) monoclonal antibodies, carrying similar VH and V alpha genes and the same IgG1 isotype, were examined for their capacity to react with several self and non-self antigens. The results showed that: (a) the anti-GAT antibodies tested reacted with different autoantigens, such as murine tubulin, actin and myosin as well as trinitrophenyl (TNP) and bovine serum albumin. Similarly, one of the anti-Alp showed weak reactivities for myosin, DNA, actin and TNP; (b) in contrast two other anti-Alp antibodies did not react with any of the tested antigens. Since the major differences between the oligoreactive anti-GAT and the monoreactive anti-Alp antibodies are in the complementarity determining regions (CDR) our results suggest that the observed cross-reactions are mediated by hypervariable loops. Sequence comparison of these antibodies indicate a possible correlation between cross-reactivity and the presence of aromatic and charged amino acids in the CDR.

Idiotypic cross-reactivity of anti-GAT and anti-alprenolol antibodies: an approach to the structural correlates of the pGAT idiotypic specificity

Most anti-GAT antibodies in the BALB/c strain express a public idiotypic specificity (pGAT), which is encoded by specific germline genes (VH10, VK5.1 and VK1A5). One or both of these germline genes, referred to as "GAT-specific genes", are also used by four anti-alprenolol antibodies. Anti-Alp and anti-GAT antibodies show no cross-reactivity for the antigens. The light chain of one anti-Alp antibody, 22C4, is encoded as the anti-GAT antibodies by a VK5.1-J2 combination and expresses part of the pGAT idiotopes, whereas the heavy chain is not "GAT"-related. Two anti-Alp using the VH10-VK5.1-J1 association do not express any of the pGAT idiotopes. Sequence comparison of the various CDR sequences points to the predominant role of the VH-CDR2 and VL-CDR3 for the constitution of the pGAT specificity. Regarding VL-CDR3, a drastic change in idiotypic determinants appears to be linked to V-J junctional diversity.

Shared idiotopes between anti-class II monoclonal antibodies and major histocompatibility complex recognition site of T cells

We have raised a number of monoclonal antibodies (mAb) against idiotopes (Id) on monoclonal anti-murine class II (anti-Ak or Ek) antibodies. Two anti-Id mAb among 31 were found to cross-react with some T cells but not with macrophages and B cells of H-2k animals. They were able to block syngeneic mixed lymphocyte reaction (SMLR) and antigen-induced major histocompatibility complex (MHC)-restricted T cell proliferation of H-2k but not of other haplotypes. These results indicated that antibodies were recognizing Id associated with the MHC restriction site of T cells. The injection of these anti-Id mAb into H-2k mice resulted in the stimulation of self-class II-reactive T cell clones as determined by SMLR. They were also able to stimulate in non-H-2k strains to prime H-2k alloreactive T cell clones. Some animals developed anti-class II (anti-Iak) antibodies by the injection of anti-Id. These results indicated that certain anti-Id (anti-anti-class II) antibodies cross-reacted with T cell receptors which carried class II restriction specificity and were involved in allorecognition. These antibodies were found to have an ability to alter the T cell repertoire in vivo by stimulating such MHC-restricted clones.

Molecular interactions in the "GAT" idiotypic network: an approach using synthetic peptides

In order to approach some of the dominant epitopes which are recognized in the GAT (Glu60 Ala30Tyr10)n random terpolymer, a variety of peptides containing 7 to 14 residues were synthesized using glutamic acid and tyrosine as building blocks, and thus were able to mimic determinants common to GAT and GT (Glu50Tyr50)n. One decapeptide and on dodecapeptide were found to inhibit GT-mAb1 (or mAb1') binding to the same extent as GAT. Antibodies were also raised against synthetic peptides which reproduced the sequence of the 6 CDR of the germline anti-GAT Ab1 antibody. Antibodies were obtained against all peptides except L1, and were shown to recognize the native Ab1-Fab. Surprisingly, some of these antibodies also recognized GAT, i.e. anti-L2, anti-H2 and anti-H3, an observation which speaks in favour of a triggering of the idiotypic network at the Ab3 level. Finally, a monoclonal antibody derived from an immunization with an Ab2-D region synthetic peptide was found to be of the Ag+Id- type. Sequence data indicate that the light chain at least is completely different from that the of Ab1/Ab1', which uses only a very precise pair of V germline genes.

Genetic basis for expression of the idiotypic network. One unique Ig VH germline gene accounts for the major family of Ab1 and Ab3 (Ab1') antibodies of the GAT system

Ig germline genes have been isolated from recombinant clones prepared in separate libraries constructed from adult BALB/c liver DNA either in pBR328 plasmid or in EMBL 3 phage. Three clones that gave a very strong positive hybridization signal with a VH anti-GAT-specific probe were completely characterized and sequenced. All three were greater than 95% homologous, with the exception of the 5' noncoding region, which was only 85% homologous but contained characteristic regulatory signals. One of these genes, H10, had a sequence that was completely identical to that of a cDNA derived from a GAT-specific BALB/c hybridoma. Southern blot analysis using Eco RI-digested DNA from rearranged GAT-specific hybridomas revealed that the same gene was used for other GAT-specific VH regions, including one differing from the H10 sequence by 12 nucleotides, which must have been generated by a somatic mechanism. The same H10 germline gene was also used, in most cases without any nucleotide substitution, in hybridomas of the Ab1' set of the GAT idiotypic cascade, suggesting that immunization with Ab2 (antiidiotypic) antibodies preferentially stimulates the direct expression of VH germline genes. Finally, the previous hypothesis that NPa and GAT VH genes were derived from the same germline gene was definitively confirmed, both from sequence data and Southern blot analysis.

A structural basis for the internal image in the idiotypic network: antibodies against synthetic Ab2-D regions cross-react with the original antigen

In the idiotypic cascade initiated by the random terpolymer (Glu60Ala30Tyr10)n or "GAT", we have identified, in the D region of Ab2 antibodies, either Glu-Glu-Tyr or Tyr-Tyr-Glu sequences which mimic GAT immunodominant epitopes, thus suggesting a structural basis for the internal image. Peptides containing the two D-region characteristic sequences were then synthesized and coupled to BSA. In mice, they elicited antibodies, a fraction of which recognized GAT. These observations speak in favour of the localization of an internal image of the GAT antigen in the D region of Ab2 antibodies.

Gene repertoire of the anti-poly(Glu60Ala30Tyr10) (GAT) immune response: comparison of VH, V kappa, and D regions used by anti-GAT antibodies and monoclonal antibodies produced after anti-idiotypic immunization

Eight monoclonal antibodies were selected from BALB/c mice immunized with two different monoclonal anti-idiotypic antibodies recognizing two discrete idiotopes characteristic of the anti-poly(Glu60Ala30Tyr10) (GAT) antibody response. These monoclonal antibodies were previously classified as Ab1 (anti-GAT-like) and Ab3 (anti-anti-idiotype) on the basis of expression of the public idiotypic specificity (p.GAT) studied with a xenogeneic serum, anti-GAT activity, and expression of various public idiotopes. All the heavy chain variable region (VH) sequences from Ab1 are nearly identical to the VH sequences of Ab1 anti-GAT monoclonal antibodies. The same type of results has been found with the Ab1 kappa light chain variable region (V kappa) sequences. Confirming our classification, Ab3 VH and V kappa sequences were found to be completely different from Ab1 VH and V kappa sequences. The Ab1 diversity (D) regions are different from one another and different from the D regions found on monoclonal anti-GAT antibodies but function similarly. These D regions are not simply derived from already described D genes. Finally, our results suggest that in the anti-GAT response VH and V kappa sequence are mainly responsible for idiotype expression.

Immune response against poly(Glu60,Ala30,Tyr10) (GAT): immunization with monoclonal anti-idiotypic antibodies leads to the predominant stimulation of idiotypically similar immunoglobulins with anti-GAT activity

Two monoclonal anti-idiotypic antibodies (HP-Id20 and HP-Id22) recognizing two different public idiotopes expressed in the anti-poly(Glu60,Ala30,Tyr10) (GAT) response were used to immunize BALB/c and C57BL/6 mice. From these animals hybridomas were isolated. From BALB/c and C57BL/6 mice eight and seven monoclonal antibodies were characterized, respectively. The reagents were classified according to the expression of the public idiotypic specificity p.GAT (recognized by a rabbit antiserum). The anti-GAT activity and the expression of the various idiotopes characterized on anti-GAT polyclonal and monoclonal antibodies were also studied. Most of the reagents are Ab1'-type of antibody resembling anti-GAT antibodies. One anti-anti-idiotypic monoclonal antibody (Ab3) was also isolated from BALB/c mice. This suggests that in this experimental model the repertoire induced after HP-Id immunization and antigen stimulation is comparable. The idiotypic analysis of a large number of anti-GAT and of Ab1' monoclonal antibodies suggests that only two public idiotopes are involved in the anti-GAT response.

Induction by monoclonal anti-idiotypic antibodies of an anti-poly(Glu60 Ala30 Tyr10) (GAT) immune response in GAT-responder and GAT-nonresponder mice

Two different monoclonal anti-idiotypic (Id) antibodies, HP-Id20 and HP-Id22, recognizing two discrete idiotopes characteristic of the anti-poly(Glu60 Ala30 Tyr10) (GAT) response were used to immunize BALB/c (GAT-responder) and DBA/1 (GAT-nonresponder) mice. The monoclonals were injected either copolymerized with keyhole limpet haemocyanin or polymerized with glutaraldehyde. The specific response was studied by two assays: (a) inhibition of binding of monoclonal anti-GAT antibody G5Bb2-2 to HP-Id20 and HP-Id22 and (b) GAT binding assays. In BALB/c GAT-responder mice, HP-Id20 and HP-Id22 immunization led to the preferential stimulation of immunoglobulin idiotypically related to anti-GAT antibodies (Ab1') and expressing anti-GAT activity. The results obtained with BALB/c nu/nu mice indicated that this response is T-cell-dependent. By means of the same experimental protocol GAT-nonresponder animals could be induced to produce anti-GAT antibodies after HP-Id immunization. This last result indicates that anti-Id immunization can bypass Ir gene control and does not preferentially stimulate the induction of GAT-specific T suppressor cells.

Immune response induced by a single or several syngeneic monoclonal antiABPC48 antiidiotypic antibodies: no predominant coexpression of ABPC48 idiotopes

BALB/c mice were immunized with monoclonal BALB/c antibodies IDA10, IDA16 and IDA17 raised against the BALB/c ABPC48 myeloma protein. Several procedures of immunization--copolymers with lipopolysaccharide or keyhole limpet hemocyanin, simultaneous or sequential injections of different IDAs--were performed in an attempt to orient the immune response towards the production of ABPC48-like idiotypes. We used a binding assay which identifies two idiotopes on the same molecule to measure the population of antibodies induced in these responses. The expression of ABPC48 cross-reactive idiotypes in immune sera was analyzed. The results show that, with all immunization protocols, immune responses to different monoclonal antiidiotypic antibodies are mostly independent of each other: the coexpression of ABPC48 idiotopes, either private or recurrent on the induced antibodies, is rarely found; it makes it difficult to discriminate by a serological approach between cross-reactive idiotypes and anti-antiidiotypic antibodies. We discuss the interest of combining molecular and serological approaches to identify these two populations of antibodies.

Characterization of monoclonal antibodies against prostaglandin E2: fine specificity and neutralization of biological effects

The specificity and heterogeneity of the immune response of BALB/c mice immunized with prostaglandin E2 (PGE2) coupled to thyroglobulin was studied. All the animals (n = 50) responded to PGB2, a transformation product of PGE2. However, following repeated injections most of the animals (n = 30) were also able to respond to PGE2. Cellular hybridizations were performed and five anti-PGE2 monoclonal antibodies were isolated and analysed. They are mainly directed against the ring and the omega-chain of PGE2 but their specificity toward the alpha-chain is more limited. The association constants are greater than to 1 X 10(9) M-1. The monoclonal antibody 8E.57.71 (Ka = 1.3 X 10(10) M-1) is particularly convenient for sensitive radioimmunoassays (detection limit 25pg/ml, when iodinated tracer is used). Anti-PGE2 monoclonal antibodies were found to neutralize the specific binding of [3H]PGE2 to rat brain hypothalamic receptors and to inhibit the PGE2 induction of rat fundus muscular contraction.

The internal image and the structural idiotypic network (Ab1, Ab2, Ab3) in the GAT system

The GAT repertoire expressed at the different levels of the classical idiotypic cascade Ag----Ab1----Ab2----Ab3 has been analysed by direct nucleotide sequencing of H- and L-enriched mRNA. Ab1 and Ab3 expressing the major public idiotypes used similar, if not identical, VH and VK genes. The VH Ab3 of the Ab1 type (Ab1') appeared highly conserved. Ab2 also use a small number of germ-line genes. The D region of Ab2 is of particular interest since it contains either a Tyr-Tyr-Glu or a Glu-Glu-Tyr sequence, characteristic of the GAT major determinants. It is therefore suggested that this D region contains the internal image of the antigen. A large number of VH germ-line genes have been isolated and sequenced. They all pertain to the VH-II family, which contains a large number of members, some of them being very close in sequence.

Poly(Glu60,Ala30,Tyr10) (GAT)-specific T cells do not express B cell public idiotopes but can be primed by monoclonal anti-idiotypic antibodies

Eight monoclonal anti-idiotypic antibodies directed against public idiotopes have been further characterized: (a) they bind to public idiotopes with a high affinity; (b) they recognize all anti-poly(Glu60,Ala30,Tyr10) (GAT) antibodies as measured by inhibition of the anti-GAT plaque-forming cell response. This has been verified in three strains of mice. These reagents were not able to detect idiotope expression on eight GAT-specific helper T cell lines and clones. This result was obtained by two techniques: (a) idiotope expression at the T cell surface was measured by indirect immunofluorescence using a cell sorter with surface antigens H-2D, Thy-1.2, Lyt-1 and L3T4 as positive controls; (b) after immunoadsorption of [35S] methionine-labeled cellular extracts from two lines, no unique molecule was retained by the HP-idp22 monoclonal anti-idiotypic antibody coupled to Sepharose. Despite these negative results, this antibody was found to prime lymph node cells in vivo, which were able to proliferate specifically in response to GAT. Two T cell lines derived from this lymphocyte population do not express any of the idiotopes tested. These results suggest that monoclonal anti-idiotypic antibodies may be influencing T lymphocyte activity indirectly.