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

Discrete bathochromic shifts exhibited by fluorescein ligand bound to rabbit polyclonal anti-fluorescein Fab fragments

Eleven individual hyperimmune rabbit polyclonal anti-fluorescein Fab fragment preparations were resolved into heterogeneous subfractions based on differential dissociation times from a specific adsorbent. Four Fab subfractions (i.e., 0.1-, 1.0-, 10-, and 100-day elutions) that differed in affinity were characterized and classified according to the extent of the bathochromic shift in the absorption properties of antibody-bound fluorescein ligand. Absorption maxima of bound fluorescein were shifted in all cases to two distinct narrow ranges, namely, 505 to 507 nm or 518 to 520 nm relative to 491 nm for free fluorescein. There was no direct correlation between the two spectral shift populations and antibody affinity, fluorescence polarization, fluorescence quenching, or fluorescence lifetimes of bound ligand. Fluorescence emission maxima varied with the bathochromic shift range. Bound fluorescein ligand, with absorption maxima of 505 to 507 nm and 518 to 520 nm showed fluorescence emission maxima of 519 to 520 nm and 535 nm, respectively. The two spectral shift ranges differed by approximately 14 to 15 nm and/or energies of approximately 1.5 kcal mol(-1) relative to each other and to the absorption maximum for free fluorescein. Spectral effects on the antibody-bound ligand were discussed relative to solvent-water studies and the atomic structure of a high-affinity liganded anti-fluorescein active site.

Resolution of rabbit polyclonal anti-fluorescein Fab (IgG) fragments into subpopulations differing in affinity and spectral properties of bound ligand

Fab fragments derived from ten different IgG populations of hyperimmune rabbit polyclonal anti-fluorescein antibodies were further resolved into subfractions based on differences in time-dependent dissociation from an FITC-adsorbent in the presence of 0.1 M fluorescein at 4 degrees C. Fab fragments separated into subpopulations based on specific dissociation times of 0.1 day, 1.0 day, 10 days and 100 days from the adsorbent. Finally, after the 100 days elution step incubation with 6.0 M guanidine-HCl was included to determine total protein concentration of specific anti-fluorescein Fab fragments. Yields of specifically eluted Fab fragments ranged from 12.7 to 84.1% of the total Fab population originally incubated with the adsorbent. All Fab polyclonal populations and subpopulations analyzed quenched the fluorescence of the bound ligand by 90% or greater. None of the plots of protein concentration versus percent yield of the total specific antibody obtained for each of the five resolved fractions constituting a specific polyclonal population conformed to Gaussian distributions. All resolved Fab subpopulations retained bound fluorescein ligand that exhibited significant bathochromic shifts in absorbancy. Based on the extent of the red-shift the antibodies segregated into one of two general spectral families showing either a peak shift to 505-507 nm or to 518-520 nm. The red-shift to 518-520 nm appeared unique to rabbit anti-fluorescein antibodies, since corresponding large shifts have not been observed with antibodies derived from other species (e.g. mouse, rat, chicken, etc.). K(d) values determined for the resolved fractions confirmed a continuous progression in affinity from the 0.1day through the 100 days elution. Preliminary isoelectric focusing analyses revealed progressive selection for relatively more homogeneous fractions, especially in the 100 days resolved fraction.

Effects of secondary forces on a high affinity monoclonal IgM anti-fluorescein antibody possessing cryoglobulin and other cross-reactive properties

The effects of secondary forces on monoclonal IgM anti-fluorescein antibody 18-2-3 reactivity were investigated and the results correlated with similar studies characterizing anti-fluorescein mAbs 4-4-20 and 9-40. mAb 18-2-3 was considered an important model for further elucidation of secondary forces since it possessed ligand binding properties similar to mAb 4-4-20, such as a similar affinity, but due to a very different primary structure it was idiotypically and metatypically distinct. mAb 18-2-3 also possessed cryoglobulin (anti-Ig) and extensive cross-reactive properties (e.g. anti-phenyloxazolone) suggestive of an atypical anti-fluorescein active site. The reactivity of mAb 18-2-3 with model fluorescein-peptides was modulated by secondary forces in a manner that differed from both mAbs 4-4-20 and 9-40. Thus, the effects of secondary forces seemed to vary with each monoclonal antibody even though each of the immunoglobulins studied were specific for the same homologous ligand. Results indicated that secondary forces impacted immune complex stability, variable domain conformation and protein dynamics. Models were postulated to account for secondary effects on the mAb 18-2-3 active site relative to mAbs 4-4-20 and 9-40. Levels of hydration, active site architecture and local amino acid dynamics were among the models cited.

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.

Anti-metatype antibody stabilization of Fv 4-4-20 variable domain dynamics

Anti-metatype (anti-Met) antibodies are immunoglobulins that specifically recognize and stabilize antibodies in their liganded or metatypic state, but lack specificity for either the hapten or the unliganded antibody. Autologous anti-Met antibodies were previously observed in vivo, suggesting that a metatypic autoantibody response could play a physiological role in the immune network, e.g. controlling the clearance of immune complexes from circulation. The first elicited anti-Met antibodies were against the fluorescein-liganded high affinity murine anti-fluorescein monoclonal antibody 4-4-20. The fluorescein-hapten system has proved to be an invaluable tool for both the recognition and characterization of the metatypic response by utilization of its spectral properties. In this investigation, hydrostatic pressure measurements, in conjunction with fluorescence spectroscopy, were performed on the recombinant Fv derivative (Fv 4-4-20) of the high affinity anti-fluorescein monoclonal antibody 4-4-20 complexed to anti-Met antibodies to study the influence of anti-Met antibodies of Fv 4-4-20 intervariable domain interactions. Anti-Met antibodies bound to liganded Fv 4-4-20 were observed to cause a change in the fluorescence properties of fluorescein that was not observed when anti-Met antibodies were bound to the liganded parent immunoglobulin. The variation of these spectral properties upon addition of anti-Met antibodies was shown to be correlated with dissociation of the variable domains in Fv 4-4-20 in response to its interaction with the anti-Met antibody. The ability to cause variable domain dissociation was dependent on whether monoclonal or polyclonal anti-Met antibodies were bound to the metatype. A model was proposed that elucidated the interaction of anti-Met antibodies, polyclonal and monoclonal, with variable domains of the primary anti-antigen antibody.

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.

Comparative properties of the single chain antibody and Fv derivatives of mAb 4-4-20. Relationship between interdomain interactions and the high affinity for fluorescein ligand

Recombinant Fv derivative of the high affinity murine anti-fluorescein monoclonal antibody 4-4-20 was constructed and expressed in high yields, relative to the single chain antibody (SCA) derivative (2 3-fold), in Escherichia coli. Both variable heavy (VH) and variable light (VL) domains, that accumulated as insoluble inclusion bodies, were isolated, denatured, mixed, refolded, and affinity-purified to yield active Fv 4-4-20. Affinity-purified Fv 4-4-20 showed identical ligand binding properties compared with the SCA construct, both were slightly lower than the affinities expressed by Fab or IgG 4-4-20. Proper protein folding was shown to be domain-independent by in vitro mixing of individually refolded variable domains to yield functional Fv protein. In solid phase and solution phase assays, Fv 4-4-20 closely approximated the SCA derivative in terms of both idiotype and metatype, confirming identical active site structures and conformations. The equilibrium dissociation constant (Kd) for the VL/VH association (1.43 x 10(-7) M), which was determined using the change in fluorescein spectral properties upon ligand binding, was relatively low considering the high affinity displayed by the Fv protein for fluorescein (Kd, 2.9 x 10(-10) M). Thus, domain-domain stability in the Fv and SCA 4-4-20 proteins cannot be the sole cause of reduced affinity (2-3-fold) for fluorescein as compared with the Fab or IgG form of 4-4-20. With their identical ligand binding and structural properties, the decreased SCA or Fv affinity for fluorescein must be an ultimate consequence of deletion of the CH1 and CL constant domains. Collectively, these results verify the importance of constant domain interactions in antibody variable domain structure-function analyses and future antibody engineering endeavors.

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.

Effects of secondary forces on the primary antibody-ligand interaction

The binding efficiency of high affinity monoclonal antifluorescyl antibody 4.4-20 with the homologous ligand situated in different protein environments has been investigated to quantitate the effect of non-active site secondary factors. To synthesize monofluoresceinated proteins, fluorescein 5-isothiocyanate was reacted with a 100-fold molar excess of ribonuclease, lysozyme, lactalbumin and bovine serum albumin. Absorption and emission spectra, as well as fluorescence life-time measurements which yielded discrete components and proteolytic studies suggested that fluorescein was conjugated to a specific lysine residue consistent with a non-random distribution of lysines within each protein population. The derivatized residue was probably a surface moiety based on accessibility analyses with iodide as a dynamic quencher. Dissociation rate analyses indicated that the relative release time of 4.4-20 with each monofluoresceinated protein was Fl-RNAse > or = Fl-lyso > or = FDS > Fl-lact > or = Fl-BSA which correlated with changes in free energy of binding. Relative fluorescence quenching measurements of the fluorescein moiety indicated that 4.4-20 showed decreasing quenching in the order FDS > Fl-RNAse > Fl-lyso > or = Fl-lact > Fl-BSA. Because spectral data indicated that fluorescein was conjugated to a specific residue or a non-random distribution of residues in each protein population, the results represented the effect of a single distinct environment or a weighted average of different microenvironments. Results have been interpreted within the theoretical framework of a dynamic antibody model involving conformer selection and the relative effects of primary and secondary interactions.

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.