Inter-relationship between immunoglobulin idiotype and metatype

Monoclonal antibodies generated against an affinity-labeled immune complex of an anti-bile acid metabolite antibody: an approach to noncompetitive hapten immunoassays based on anti-idiotype or anti-metatype antibodies

Conventional immunoassays for haptens such as steroids and synthetic drugs are dependent on the competitive reaction between an unlabeled antigen (analyte) and a labeled antigen against a limited amount of anti-hapten antibody. Although noncompetitive immunoassay procedures such as two-site immunometric assays offer a much higher sensitivity, direct application of this principle to haptens has been difficult due to their small molecular mass precluding simultaneous binding by two antibody molecules. Here, we have attempted to develop a noncompetitive immunoassay system based on anti-idiotype or anti-metatype antibodies. Ursodeoxycholic acid 7-N-acetylglucosaminide (UDCA 7-NAG), which is a bile acid metabolite (molecular weight, 595.8), was selected as the model hapten. A/J mice were immunized with a monoclonal antibody against UDCA 7-NAG, which had been affinity-labeled with a relevant hapten derivative. The fusion between the immune spleen cells and P3/NS1/1-Ag4-1 myeloma cells yielded four kinds of alpha-type and two kinds of beta-type monoclonal anti-idiotype antibodies, each recognizing the framework region and paratope of the anti-hapten antibody. The use of a selected combination between alpha-type and beta-type antibodies together with the anti-hapten antibody provided a noncompetitive assay system with a subfemtomole order sensitivity (detection limit, 118 amol) and a practical specificity.

Effects of secondary forces on the ligand binding properties and variable domain conformations of a monoclonal anti-fluorescyl antibody

Biochemical interactions occurring external to the antibody active site or pocket (i.e. secondary forces) that directly effect ligand binding efficiency, and the microenvironment-sensitive spectral properties of bound homologous ligand, residing within the active site of high affinity monoclonal antifluorescyl antibody (mAb) 4-4-20, have been previously reported. This study describes the synthesis and characterization of a series of specially designed and chemically distinct mono-fluoresceinated peptides of equal size (13-mer) as well as the changes in the spectral properties and free energy in the binding of each fluorescein derivatized peptide, upon interaction with mAb 4-4-20. Significant differences in binding efficiency and fluorescence quenching of the ligand, as well as the intrinsic tryptophan fluorescence, were observed for each monofluoresceinated peptide relative to one another and fluorescein ligand. In addition to the effects on the fluorescence quenching of fluorescein and intrinsic tryptophan residues, and the free energy of binding, the conformation of the variable domains of mAb 4-4-20 upon interaction with the fluoresceinated peptides was probed with polyclonal antimetatype (conformational dependent anti-liganded state) antibodies. Studies comparing the results of a solid-phase inhibition assay, with the binding of antimetatype antibodies in solution, suggested that variant metatypic states of mAb 4-4-20 resulted from binding of the various fluorescein derivatized peptides. Depiction of the mAb 4-4-20 active site as a series of thermally averaged substates is proposed as a model and framework to interpret further the results. It was concluded that secondary forces can dictate conformer selection from the various substates. thereby modulating the primary antibody ligand interaction.

Antibody networks and imaging: elicitation of anti-fluorescein antibodies in response to the metatypic state of fluorescein-specific monoclonal antibodies

Studies are described regarding generation of anti-hapten antibodies starting with a monoclonal Ig immunogen in the ligand-induced conformation or metatypic state. Liganded monoclonal Ab1 antibodies represent the unique feature of the study since previous reports investigating internal imaging in the original Idiotype Network Hypothesis [Jerne, 1974 (Ann. Immun. 125C, 373-389)] were based on the non-liganded or idiotypic state [as reviewed in: Rodkey, 1980 (Microbiol. Rev. 44, 631-659); Kohler et al., 1979 (In: Methods in Enzymology: Antibodies, Antigens and Molecular Mimicry, pp. 3-35); Greenspan and Bona, 1993 (FASEB J. 7,437-444)]. Affinity-labeled liganded murine monoclonal anti-fluorescein antibodies served as immunogens administered both in the syngenic and xenogenic modes to determine if the metatypic state elicited anti-hapten antibodies through imaging-like mechanisms. Polyclonal and monoclonal anti-Ab1 reagents in various hosts were assayed for anti-fluorescein and/or anti-metatype specificity. Significant anti-fluorescein responses were measured indicating that the metatypic state directly or indirectly stimulates an anti-hapten antibody population.

Temperature and pH dependence of fluorescein binding within the monoclonal antibody 9-40 active site as monitored by hydrostatic pressure

In a comparative study, the thermodynamic parameter, DeltaV, was obtained using hydrostatic pressure-induced dissociation of fluorescein (Fl) from the active site of monoclonal antibody (mAb) 9-40 and its mutant and native derivatives equilibrated at six pH values (8.0, 7.5, 7.0, 6.5, 6.0, and 5.5) and four temperatures (35, 25, 15, and 5 degrees C). mAb 9-40 and its Fab and single-chain Fv (scFv) derivatives at pH 8.0 were found to have identical Fl dissociation behavior under pressure as a function of temperature. The pressure dissociation at 25 degrees C as a function of pH showed a sigmoidal dependence of DeltaV with a midpoint value at pH 7.4 for mAb 9-40. Comparison of experimental results for scFv 9-40/212 with its mutant scFv 9-40/212Arg-34L indicated that the pH dependence of mAb 9-40 was due to the titration of His-34L in the active site. Iodide quenching of bound Fl showed that the hapten in this active site was solvent accessible. Imperfect packing, which leads to increased conformational dynamics, was determined as a possible cause of the low affinity for mAb 9-40.

Perturbation of antibody bound bifluorescent-ligand probe by polyclonal anti-metatype antibodies interacting with epitopes proximal to the liganded antibody active site

General localization of metatypic determinants recognized by polyclonal anti-metatype antibodies relative to the antibody active site of the high-affinity anti-fluorescein monoclonal antibody 4-4-20 was achieved through use of a unique bifluorescent-ligand probe. The fluorescent probe possessed intrinsic energy-transfer properties with the fluorescein hapten serving as the energy acceptor. The donor group 5-(2-iodoacetyl) aminoethylaminonaphthalene-1-sulfonic acid (IAEDANS) proved environmentally sensitive both to binding of the FITC-cys-AEDANS ligand and to subsequent anti-metatype antibody interactions involving the antibody variable domains of 4-4-20. Spectral changes in ligand-conjugated AEDANS upon specific reactivity of the antibody with FITC suggested secondary interactions between AEDANS and the topological protein surface adjacent to the 4-4-20 active site. Results indicated that some anti-metatype antibodies (Fab fragments) within the polyclonal population bound to sites immediately surrounding the liganded active site and perturbed the interactions of AEDANS with topological sites. The results are discussed in terms of the types of interactions that may occur between the AEDANS moiety and the 4-4-20 antibody protein surface and subsequent perturbation of those interactions by anti-metatype antibodies.

Primary structures of three Armenian hamster monoclonal antibodies specific for idiotopes and metatopes of the monoclonal anti-fluorescein antibody 4-4-20

This paper reports the complete V gamma, V kappa, C gamma 1 and C kappa nucleotide and deduced amino acid sequences of two hamster monoclonal anti-metatype antibodies, 3A5-1 and 4A6. These antibodies have been previously characterized in terms of their binding and molecular stabilization properties with liganded murine monoclonal and single-chain antibody 4-4-20 active sites. Also reported are the complete V kappa and C kappa nucleotide and deduced amino acid sequence of hamster monoclonal anti-idiotype antibody 1F4, which is specific for the unliganded 4-4-20 active site. Oligonucleotide primers based on the 5' ends of murine variable genes, along with primers specific for murine IgG C gamma 1 and kappa constant region genes, have been used in cDNA and polymerase chain reactions (PCRs) to amplify IgG cDNA from Armenian hamster/mouse hybridomas. The hamster C gamma 1 and C kappa domain sequences are highly homologous to previously reported murine sequences. The anti-idiotype mAb V kappa gene demonstrated strong similarity to the murine V kappa V gene subgroup while the two anti-metatype mAb V kappa genes approximated more closely to the murine V kappa III gene subgroup. The two anti-metatype mAbs utilized highly homologous V gamma genes, with differing HCDR 3 regions, that appeared similar to the murine V gamma I(a) subgroup. These sequence determinations represent the first primary structures reported for antibodies with anti-metatype activity and are additions to the relatively sparse hamster immunoglobulin genetic database. Results are discussed in terms of 4-4-20 active site specificity and anti-metatype activity, as well as immunoglobulin structural diversity in an anti-Ig immune response.

Sandwich immunoassay for the hapten angiotensin II. A novel assay principle based on antibodies against immune complexes

Immunoassays for haptens such as short peptides or drugs are usually based on the principle of competition for a limited number of binding sites on antibody molecules. Owing to the small size of these antigens it has been thought that two specific antibodies cannot simultaneously bind a hapten. However, antisera containing so called anti-metatypic antibodies have been reported (Voss et al. (1988) Mol. Immunol. 25, 751-759) that bind to hapten-mAb complexes in a reaction where conformational changes on the primary antibody are important. Here, we report on monoclonal antibody pairs able to form ternary complexes with the octapeptide angiotensin II. The first mAb (mAb1) is conventional and binds angiotensin II with high affinity (Kd 10(-11) M). The secondary (anti-metatypic) mAbs (mAbs2s) recognize the immune complex consisting of angiotensin II bound to mAb1, but only poorly recognize mAb1 alone. An immunization technique involving tolerization with uncomplexed mAb1 was used to generate mAb2s. None of the mAbs2s were able to bind angiotensin II by themselves but all efficiently bound the complex of angiotensin II and mAb1. All mAb2s stabilized the angiotensin II-mAb1 complex and one mAb2 distinctly improved the specificity of the assay for angiotensin II. By either labelling mAb1 and immobilizing mAb2 (or vice versa) two-site immunometric assays with detection limits of 1 pg/ml angiotensin II have been established. The kinetics of the complex formation was investigated by fiber optic biospecific interaction analysis (FOBIA), a system allowing real time observation of binding events on the surface of a glass fiber. The association rate towards the liganded conformation of mAb1 was higher than towards the free mAb1. By contrast, the mAb2s dissociated at similar rates from complexed and uncomplexed mAb1.

Elicitation of distinct populations of monoclonal antibodies specific for the variable domains of monoclonal anti-fluorescein antibody 4-4-20

Armenian hamsters were immunized with non-liganded, partially liganded or affinity-labeled anti-fluorescein Mab 4-4-20. Seventeen hybridoma producing monoclonal anti-4-4-20 antibodies were characterized from chemically-mediated fusions of immune hamster lymphocytes with murine Sp2/O-Ag14 myeloma cells. Distinct populations of anti-4-4-20 monoclonal antibodies were isolated from hamsters receiving immunizations with partially liganded Mab 4-4-20 relative to those receiving affinity-labeled 4-4-20. Two of the three monoclonal antibodies produced in response to partially liganded 4-4-20 were inhibited in their interaction with 4-4-20 by fluorescyl ligand. These two clones, 1F4 and 1B7, recognized unique epitopes on the 4-4-20 molecules, as demonstrated by non-reactivity with members of the 4-4-20 idiotype family. Additionally, 1F4 and 1B7 demonstrated the ability to delay the association of fluorescein with Mab 4-4-20. The 14 characterized non-ligand-inhibitable Mabs elicited to affinity-labeled 4-4-20 were classified into four separate groups based on various binding properties with members of the 4-4-20 idiotype family and binding to resolved H- and L-chains in a western blot. Members of three of the four groups showed strong reactivity with both 04-01 Ig and 04-01 SCA, which utilizes the same L-chain as Mab 4-4-20. Six non-ligand-inhibitable Mabs, 4A6, P1E11, 3A5-1, 2C3, 2C4, and 1A4, delayed the dissociation rate of ligand from Mab 4-4-20 and mutant 4-4-20 SCA L32phe.

Characterization of interactions involving anti-metatype antibodies and immune complexes

Immunizations of high affinity anti-fluorescein monoclonal antibody 4-4-20 affinity labeled with fluorescein 5-isothiocyanate into a rabbit elicited antibodies specific for the liganded conformation of 4-4-20 (termed "anti-metatype" antibodies). Reaction of liganded 4-4-20 with anti-metatype antibodies caused significant delay (up to 23-fold) in the rate of dissociation of fluorescein ligand from the active site. In this study, structural analogues of fluorescein, including fluorescein 5-isothiocyanate, fluorescein 6-isothiocyanate, 5-dichlorotriazinyl aminofluorescein and 5-carboxyfluorescein, were bound by monoclonal antibody 4-4-20 and anti-metatype antibody reactivity was observed through delay in the dissociation rate of ligand from Mab 4-4-20. Significant delays (ranging from 5- to 242-fold) were observed for all structural analogues examined indicating that 4-4-20 maintained similar but not necessarily identical conformations upon binding fluorescein structural analogues. Additionally, fluorescein 5-isothiocyanate and fluorescein 6-isothiocyanate were conjugated to carrier molecules of increasing mol. wt (ranging from 225 to 14,600 D) in an attempt to sterically interfere with "metatopes" at the mouth of the active site and localize regions of anti-metatype antibody binding. These fluorescein-conjugated compounds were reacted with 4-4-20, and binding of anti-metatype antibodies delayed dissociation rates from 24- to greater than 1500-fold. These results indicated that the mechanism whereby anti-metatype antibodies delay the release of fluorescyl ligands from the active site probably does not solely involve steric hindrance of the ligand due to binding of anti-metatype antibodies at the mouth of the active site. Studies with 4-4-20 Fab fragments and a single chain derivative of 4-4-20 (consisting of the variable regions tethered by a 14 amino acid linker) indicated that anti-metatype reactivity was specific for the immunoglobulin variable region.

Autologous anti-metatype immune response in rabbits

Rabbits hyperimmunized with fluorescyl-conjugated KLH exhibited bound ligand associated with a high affinity circulating IgG anti-fluorescein population. After cessation of immunogen administration the liganded complexes were eventually spontaneously cleared from the circulation. Individual rabbits synthesized autologous anti-metatype antibodies specific for ligand-antibody complexes. Autologous anti-metatype antibodies reacted optimally with autologous liganded anti-fluorescein antibodies. However, cross reactivity was noted with allogenic rabbit liganded antibodies from three affinity-purified pools. An autologous anti-metatype response, reminiscent of autoanti-idiotype responses, has important implications concerning in vivo clearance of antigen-antibody complexes and may serve as a model to study immune complex diseases.

A single-step method for the purification of anti-FITC antibodies by use of a coumarin immunosorbent

Monoclonal anti-fluorescein isothiocyanate (FITC) antibody cross-reacts with 7-hydroxy coumarin derivatives conjugated to BSA. This property permitted the affinity purification of monoclonal anti-FITC antibodies from ascitic fluid using an-immunosorbent consisting of a 7-hydroxy coumarin derivative linked to Sepharose 4B. Ascitic fluid was applied to the immunosorbent column and, after washing, the bound antibody was eluted under extremely mild conditions using 3 M MgCl2. Antibody eluted in this manner was greater than 96% pure as assessed by SDS-PAGE. A polyclonal sheep anti-FITC antibody was also purified from serum on the same immunosorbent to greater than 94% purity. This simple and rapid method for the purification of anti-FITC antibodies will find applications in both immunodiagnostic procedures and in studies of hapten-antibody interactions. The affinity constant of the purified monoclonal anti-FITC antibody conjugated to horseradish peroxidase was assessed by ELISA and was found to be 1.5 x 19(9) M-1.

Anti-metatype antibody reactivity: a model for T-cell receptor recognition

Anti-metatype (Met) antibodies are anti-immunoglobulins that specifically recognize an antibody-liganded active site but lack specificity for either the ligand or the idiotype. As proposed here by Edward Voss, anti-metatype-metatype immunoglobulin interactions may serve as a model for the interaction of the T-cell receptor (TCR) with antigen-MHC (class I/class II) complexes: the anti-metatype immunoglobulin reagent simulates the TCR and the liganded antibody mimics the antigen-MHC complex. Such a model addresses the dilemma of two macromolecules interacting with the same antigenic determinant and may represent a rational approach to improve understanding of the initiation and regulation of the immune response.