Modeling study of antibody combining sites to (alpha 1-6)dextrans. Predictions of the conformational contribution of VL-CDR3 and J kappa segments to groove-type combining sites

The shuffling of the V kappa-Ox1 light chain joined to J kappa 4 of J kappa 5 instead of J kappa 2 reduced or abolished antigen binding of three groove-type anti-(alpha 1-6)dextran monoclonal antibodies, raising questions as to the structural roles of J kappa in antibody combining sites. The J kappa 4 light chain used contains Pro95A at the V kappa-Ox1-J kappa 4 junction, as well as a Phe to Ile substitution at the beginning of this J kappa 4 segment. To predict whether the defect in antigen binding is a consequence of the J kappa replacement, the Pro insertion or the Phe to Ile substitution, model-building studies were performed. As shown by the surface representation of antibody combining sites, the models with length variation in the VL-CDR3 loop by only 1 residue altered the shape of the combining site dramatically; whereas those with replacement of J kappa or having amino acid substitutions in VL-CDR3 affect the combining site less extensively. A distinct loop configuration of VL-CDR3 appears in models having either a Pro, Gly, or Ala insertion at position 95A. These results indicate that the length of VL-CDR3 is crucial for its loop conformation and may, therefore, have played a major role in abolishing dextran binding activity of the J kappa 4 variants. The potential of V kappa-Ox1 genes in generating conformational diversity in the loop of VL-CDR3 and its influence in forming different combining sites are discussed.

Prolyl isomerases catalyze antibody folding in vitro

Some slow-folding phases in the in vitro refolding of proteins originate from the isomerization of prolyl-peptide bonds, which can be accelerated by a class of enzymes called prolyl isomerases (PPIs). We used the in vitro folding of an antibody Fab fragment as a model system to study the effect of PPI on a folding reaction that is only partially reversible. We show here that members of both subclasses of PPIs, cyclophilin and FK 506 binding protein (FKBP), accelerate the refolding process and increase the yield of correctly folded molecules. An acceleration of folding was not observed in the presence of the specific inhibitor cyclosporin A, but still the yield of correctly folded molecules was increased. Bovine serum albumin (BSA) increased the yield comparable to cyclophilin but, in contrast, did not influence the rate of reactivation. These effects were observed only when cyclophilin or BSA were present during the first few seconds of refolding. However, the rate-limiting reactivation reaction is still accelerated when PPI is added several minutes after starting refolding. In contrast, the prokaryotic chaperone GroEL influences the refolding yield when added several minutes after initiating refolding. The results show that PPIs influence the folding of Fab in two different ways. (1) They act as true catalysts of protein folding by accelerating the rate-limiting isomerization of Xaa-Pro peptide bonds. Proline isomerization is obviously a late folding step and has no influence on the formation of aggregates within the first seconds of the refolding reaction.(ABSTRACT TRUNCATED AT 250 WORDS)

Branched polypeptides as antigens for influenza virus hemagglutinin and T-cell receptor subunits

The multiple antigenic peptide (MAP) method was applied to improve the immunogenicity of synthetic peptides representing distinct regions of the influenza virus hemagglutinin (HA). A tetrameric MAP with multiply incorporated overlapping B- and T-cell epitopes was combined with a particular HA sequence representing the slightly modified fusion peptide on the C-terminus of the Lys core (MAP-1). As a result of repeated injections of BALB/c mice with MAP-1 but not with the monomeric HA1C[Arg] peptide, the appearance of MAP-1-specific antibodies crossreactive with the acid-pretreated virus could be observed. In vitro studies revealed the potency of the MAP-1 structure to induce proliferation of HA1C[Arg]-primed T-cells, and in vivo studies demonstrated the protective feature of the immune response elicited by MAP-1 and to a lesser extent by the monomeric HA1C[Arg]. The increased level of MAP-1 specific antibodies upon viral challenge shows the activation of MAP-1-specific B- and/or T-cells. The advantage of the previously verified FP3 helper T-cell epitope included in MAP-1 was further utilized to synthesize chimeric structures comprising short fragments of the zeta of (MAP-2) or delta (MAP-3) subunits of the T-cell antigen receptor (TCR) complex. The selected peptides of the zeta and delta-chain regions failed to elicit an antibody response in BALB/c mice as tetra- or octamers, but the inclusion of the modified fusion region resulted in an immunogenic construction.(ABSTRACT TRUNCATED AT 250 WORDS)

Chimeric antibodies with anti-dextran-derived complementarity-determining regions and anti-p-azophenylarsonate-derived framework regions

The framework regions of antibodies fold into a conserved beta-sheet structure that acts as scaffolding for the antigen-contacting complementarity-determining regions (CDR). To test the structural equivalence of the frameworks between two antibodies with widely different combining sites, we created chimeric H and L chains by grafting the CDR of an alpha(1-->6)dextran specific antibody onto the framework of a p-azophenylarsonate (Ars) specific antibody through oligonucleotide-directed mutagenesis of the anti-Ars variable region genes. Antibodies consisting of various chain combinations of the chimeric, anti-dextran, and anti-Ars derived H and L chains were generated in transfectomas and tested for binding to dextran and Ars. Of the newly created chimeric and/or hybrid antibodies, an antibody with the chimeric H chain and the anti-dextran L chain bound to dextran with the same association constant as the parental anti-dextran antibody, and like the anti-dextran antibody was shown by immunochemical mapping to have a site complementary to six glucose residues. None of the other new variable region combinations, including the all-chimeric combination, showed binding to either dextran or Ars. These results indicate that the H chain but not the L chain anti-dextran and anti-Ars frameworks are functionally equivalent. Attempts to confer dextran binding on the H and L chain chimeric antibody, by mutagenizing selected framework residues, were unsuccessful. This study demonstrates the important role of the frameworks in the precise alignment of the CDR for Ag binding.

Kinetic analysis of papaya proteinase omega

Papaya proteinase omega (pp omega) has been purified from dried latex both by immunoaffinity and traditional methods. Kinetic analysis revealed that (1), the pp omega-catalysed hydrolysis of N-benzoyl-L-arginine p-nitroanilide (BApNA) has a lower specificity (kcat/Km) than the same reaction catalysed by papain; (2), the pp omega-catalysed hydrolysis of a tripeptide substrate having phenylalanine at the second position (S2-site) showed a more similar specificity to that catalysed by papain; (3), the significant difference between the two enzymes is that steady state kinetics with both L-BApNA and a tripeptide enables the identification in pp omega of other ionizations affecting binding. The active sites of papain and pp omega can therefore be distinguished by pH-dependence of kcat/Km.

Cross-reactivity between murine melanoma antigen B700 and a human melanoma-associated antigen (M-66) recognized by autologous antibody: evidence suggesting shared epitopes

We have previously reported the purification and partial characterization of a human melanoma-associated antigen (M-66) recognized by autologous antibody. This antigen was found to be an unusually acidic 66 kDa glycoprotein. In studies of murine melanoma, a 67-kDa albumin-like melanoma-associated antigen (MAA) isolated from B16 melanoma cells has also been reported by our laboratories. Because the murine MAA, B700, has a molecular weight that is nearly the same as M-66, we sought to determine what similarities and differences existed between these two antigens. Human sera S150, which is known to recognize M-66, was found to bind to murine melanoma cell line B16. The addition of purified M-66 inhibited binding of S150 to B16 cells. Binding by S150 was not noted against murine melanoma cell line S91, which is known not to express cell surface B700. Conversely, reactivity of S150 against Y-Mel 84:420, known to express M-66, could be inhibited by preincubation with B16 cells. Four monoclonal antibodies known to recognize B700 were evaluated for-binding against murine B16 and human melanoma cell line Y-Mel 84:420. Binding was noted against both B16 and Y-Mel 84:420 which could be inhibited by the addition of M-66. Binding of S150 was also noted against purified B700 as tested by ELISA. While a comparison of the amino acid composition of the two antigens revealed similarities, M-66 contained 2.8 times as much serine and 0.4 times as much proline as B700. B700 has been reported to be related to serum albumin, which is not the case for M-66.(ABSTRACT TRUNCATED AT 250 WORDS)

A new method of technetium-99m labeling of monoclonal antibodies through sugar residues. A study with TAG-72 specific CC-49 antibody

We have developed a very efficient labeling technique for monoclonal antibodies with technetium-99m. Oxidation of sugar residues on the IgG class of antibodies leads to the generation of aldehyde groups which are further reacted with two newly developed hydrazide compounds. This methodology introduces sulfhydryl groups on the antibody through sugar residues which can be labeled with technetium-99m. We have studied the TAG-72 specific second generation antibody CC-49. The specific activity of the labeled antibody was high without loss of its immunoreactivity.

Engineering bispecific antibodies

Bispecific antibodies have immense potential as reagents and in medicine. Until recently, they were made by combining monoclonal antibodies of two different specificities in vitro, or by fusion of the corresponding hybridomas. Protein engineering now offers the chance to construct a range of small 'designer' bispecific antibodies using antibody fragments as building blocks.

Synthesis, metal chelate stability studies, and enzyme digestion of a peptide-linked DOTA derivative and its corresponding radiolabeled immunoconjugates

By directly coupling a tetrapeptide to DOTA through an amide bond, we synthesized a novel DOTA derivative, DOTA-glycylglycylglycyl-L-p-nitrophenylalanine amide. We converted this new precursor bifunctional chelating agent to DOTA-glycylglycylglycyl-L-p-isothiocyanatophenylalanine++ + and conjugated it to monoclonal antibody Lym-1. Serum stability studies show that the radiolabeled conjugates are kinetically inert under physiological conditions. The rates of loss of radiometals in human serum are 0.1 +/- 0.1% per day for InIII, 0.02 +/- 0.15% per day for YIII, and 0.3 +/- 0.2% per day for CuII labeled immunoconjugates. In the presence of the liver enzyme cathepsin B, an in vitro digestion of 114mIn-labeled conjugate yields a small fragment containing 114mIn. Characterization of the cleavage products shows that this liver enzyme hydrolyzes the peptide linkage before the phenylalanine residue, freeing the In-DOTA-triglycine complex from the conjugate. However, the liver enzyme cathepsin D does not cleave the linkage over the span of 7 days.

Liquid-liquid partition chromatography as a method to examine surface properties of antibodies and antigen-antibody complexes

We demonstrate liquid-liquid partition chromatography in aqueous two-phase systems (LLPC) as a simple method for examining the surface properties of immunoglobulins and antigen-antibody complexes in solution. LLPC separates molecules with respect to the properties of the exposed surfaces. As an example, the method may be used to detect changes in the conformation of IgG following chemical modification like acylation or iodination. We have studied the partitioning of antibodies and antigen-antibody complexes, modelled by rabbit antibodies against three human serum proteins, in aqueous polyethylene glycol/dextran two-phase systems at pH 7. Analysis of both polyclonal and monoclonal antibodies against various antigens suggested that the partition properties of immunoglobulins are related mainly to their antigen specificity and not to subclass-specific structures. Furthermore, experiments indicated that changes in the surface properties of antigen and/or antibody following complexation may be detected. Thus, LLPC may prove to be a new way of studying the relation between antibody structure and function in solution.

[The use of the physicochemical laws governing the sorption properties of antigens (antibodies) in relation to the plastic solid phase for enhancing the sensitivity of immunoenzyme analysis test systems in the diagnosis of infections]

Some practical aspects of the theory of adsorption of bioligands on plastic surfaces have been considered and discussed. Modifications of experimental and actual antigens (antibodies) have been theoretically and practically realized on the concept of "solubility parameters" by means of pin-point hydrophobization. The use of this method has been shown to increase the sensitivity of individual ELISA systems based on rabbit and mouse immunoglobulins 1.5- to 2-fold; the sensitivity of the assay system for the evaluation of HBsAg increases 8- to 10-fold. Theoretical calculations making it possible to map out the ways to further increase the sensitivity of different ELISA systems are given.

Evaluation of mutagenesis for epitope mapping. Structure of an antibody-protein antigen complex

The location and description of epitopes on proteins describe the basis of immunological specificity. The 2.8-A structure of the phosphocarrier protein, HPr from Escherichia coli, complexed to the Fab fragment of the monoclonal antibody, Jel42, has been determined. This allows the first comparison of epitope predictions from extensive site-directed mutagenesis experiments, coupled with biological activity studies (Sharma, S., Georges, F., Klevit, R. E., Delbaere, L. T. J., Lee, J. S., and Waygood, E. B. (1991) Proc. Natl. Acad. Sci. U.S.A. 88, 4877-4881), with those from x-ray analysis. There are 14 amino acid residues of E. coli HPr that interact with the Jel42 antigen-binding site. Nine of these were correctly assigned by the mutagenesis studies. Of the 5 remaining residues, Met-1 could not be altered; two others appear to have critical roles in determining protein conformation; the other 2 residues have a minimal effect on antibody binding since they are located on the periphery of the epitope with one face of their side chains in van der Waals contact with the antibody and the other face in contact with solvent. Four residues were incorrectly assigned to the epitope. These residues were located adjacent to epitope residues that were likely perturbed by these mutations. This study demonstrates that mutations which caused greater than 10-fold changes in antibody binding affinity were correctly assigned to the epitope by the mutagenesis experiments. Guidelines are also presented in order to minimize incorrect assignments.

Determination of fibrinogen in plasma by high-performance immunoaffinity chromatography

A high-performance immunoaffinity chromatographic (HPIAC) method for fibrinogen was developed which had several advantages over existing methodologies including increased linear range and no interference from heparin. Several modifications of usual HPIAC procedures were necessary including the employment of a methacrylate polymeric support to reduce non-specific adsorption and the addition of urea to a pH 2.1 elution buffer to affect elution. A significant split-peak effect (i.e., unretained fibrinogen) was noted at higher flow-rates and at higher fibrinogen concentrations, which was shown to be temperature-dependent, with the amount of fibrinogen retained on the column increasing with increased temperature.

Length distribution of CDRH3 in antibodies

Sequences of the third complementarity determining region of antibody heavy chains (CDRH3s) are listed according to their length. Human sequences vary from 2 to 26 amino acids residues, but less extensively in other species. When combined with the other five complementarity determining regions, this enormous length variation of CDRH3, together with amino acid substitutions in their sequences, can provide a very large number of antibody specificities and can influence the shape of antibody combining sites.

Regeneration of antidigoxin binding activity in an antibody by changes surrounding the original binding defect

A panel of antibodies which differ in their L chain structures and which bind to structurally defined haptens, would be useful in investigating L chain structure and function. In a previous study, chain recombinant antibody CR24 (26-10 H, 45-20 lambda) was produced by hybridoma-hybridoma fusion. Although both parental antibodies bound digoxin with high affinity, CR24 lacked detectable digoxin-binding activity. Hybridoma CR24 was subsequently fused with H chain-loss hybridomas in order to produce a panel of antibodies composed of 26-10 H chains and 26-10 "like" L chains. Two antibodies produced were CR260 which demonstrated digoxin-binding activity and CR256 which did not. CR260 and CR256 expressed only one amino acid difference (Pro to Leu at L-96). This difference resulted in the CR256 binding defect. In this report, two new antidigoxin antibodies are described. One, SR2E7, contained the Pro to Leu (L-96) defect, but still bound digoxin. Binding affinities and binding specificity patterns, as well as complete VL DNA sequence and corresponding protein sequence of the new digoxin binding antibody L chains (SR2E7 and SR1C7) are presented. Both kappa L chains are highly homologous to the 26-10 kappa L chain as well as the BALB/c germline gene K5.1. These results suggest that antibodies which are initially defective in binding activity can be cured by changing specific amino acids involved in determining the binding-site structure. Molecular modelling studies of the binding-site region were completed to address L chain structural changes induced by specific amino acid substitutions.

Binding kinetics of antigen by immobilized antibody or of antibody by immobilized antigen: influence of lateral interactions and variable rate coefficients

Kinetic rate expressions are developed for the binding kinetics of antigen by immobilized antibody or of antibody by immobilized antigen. The influence of lateral interactions leads to variable rate coefficients for adsorption, and these provide a more realistic picture of the events occurring on the surface. Emphasis is placed on the similarities and dissimilarities present in the kinetic rate expressions. A general trend in the rate expressions is observed on going from dual-step binding to dual-step binding with lateral interactions. This provides physical insights into the reactions occurring at the surface and helps in their control and stability at the surface.

Contact-dependent, immunecomplex-mediated lysis of hapten-sensitized liposomes

Large unilamellar liposomes (d approximately 160 nm) composed of dioleoylphosphatidylethanolamine (DOPE) (80-90%), a negatively charged phospholipid stabilizer (10-20%), and a small amount (0.1-1%) of a haptenated lipid are unusually stable in divalent cation-free isotonic buffer at pH 7.4. The liposomes can be stored under this condition at 4 degrees C for at least 6 months without any detectable leakage of the entrapped fluorescent dye calcein. However, the liposomes undergo a rapid (1 h) aggregation and lysis reaction in the presence of free bivalent anti-hapten antibody. The liposome destabilization was immunospecific in that it did not occur with the normal IgG or in the presence of excess free hapten. Liposome lysis was always accompanied by liposome aggregation. Aggregation and lysis of the liposomes was completed in 5 min if the incubation temperature was raised to 70-80 degrees C. Replacing DOPE with dioleoylphosphatidylcholine in the liposomes did not abolish the liposome aggregation, but no liposome lysis was observed even at 80 degrees C. Since liposome aggregation appeared to be a necessary (but not sufficient) prerequisite for liposome lysis, we have named this new class of liposome "contact-sensitive liposomes." The immunodiagnostic potential of the contact-sensitive liposome was demonstrated with liposomes containing theophylline-DOPE. The aggregation and lysis of the liposomes induced by a monoclonal anti-theophylline antibody could be inhibited by free theophylline at concentrations of therapeutic significance. The observation could be the basis of a homogeneous assay for theophylline.

Use of bispecific heteroconjugated antibodies (anti-T cell antigen receptor x anti-MHC class II) to study activation of T cells with a full length or truncated antigen receptor zeta-chain

Ligand-induced activation of T cells involves recognition of monovalent peptide Ag complexed with a cell surface MHC-encoded molecule. In contrast, antibody-induced activation of T cells typically requires external cross-linking of the TCR. To examine the mechanisms that underlie the ability of these different stimuli to signal, we have created bispecific chimeric antibody molecules (BA) that mimic Ag in several important aspects. Anti-TCR-alpha, -beta, or anti-CD3-epsilon Fab fragments were covalently coupled to an anti-MHC class II Fab fragment. These BA elicited IL-2 production or proliferation from Ag-specific T cell hybridoma cells or splenic T cells, respectively, in the presence, but not the absence, of accessory cells expressing the appropriate MHC class II molecule. This response was prevented by soluble blocking antibodies against the TCR or MHC class II. When "presented" by MHC class II-bearing accessory cells, anti-TCR x anti-MHC class II BA, like cell surface Ag, elicited IL-2 production from T cell transfectants expressing full length TCR zeta-chain but not from otherwise identical cells expressing truncated zeta; when immobilized on a plastic surface these BA were potent stimulators that induced equal amounts of IL-2 from the same cells. Purified Ag/MHC complexes immobilized on plastic were able to induce IL-2 production from T cells expressing the full length, but not the truncated, form of zeta. We hypothesize that TCR-mediated T cell activation requires stable aggregation of the TCR. In this model, activation by mobile cell surface Ag/MHC or BA occurs in two steps, occupancy-induced TCR clustering followed by stable aggregation facilitated by the presence of a full length zeta-chain. Immobilized high affinity anti-TCR antibodies, but not low affinity Ag/MHC complexes, directly promote stable receptor aggregates, and thus would not require a full length zeta-chain.

Effect of a human IgG preparation rich in antibodies to a wide range of lipopolysaccharides on gram-negative bacterial sepsis in burned mice

A human intravenous IgG preparation (Anti-LPS IgG) rich in antibodies to different lipopolysaccharides (LPS) and a normal human intravenous IgG (NIgG) were investigated for their ability to confer passive immunity. Both preparations were given at the time of infection (prophylaxis) or during sepsis (therapy) to burned mice with lethal infection induced by various clinically relevant gram-negative bacteria. When given at the time of infection both IgG preparations (5 mg/mouse) inhibited lethality induced by some bacteria (Pseudomonas aeruginosa serogroup G and B), but not others (Serratia marcescens, Klebsiella pneumonia, Proteus mirabilis), indicating a protection by by strain-specific antibodies. However, no significant protection was seen when mice were treated during sepsis. The range of specific antibody titers to the whole live bacteria and heat-killed (LPS-preserved) bacteria in the NIgG paralleled that of Anti-LPS IgG; however, the magnitude of the antibody titers did not accurately reflect the protective capacity in vivo. Thus, the exact specificity of the protective antibodies is still unknown. The protective effect of both IgG preparations was dose-dependent; at low IgG doses (0.5 mg/mouse) better protection was obtained with Anti-LPS IgG, whilst at higher doses (> or = 1 mg/mouse) both preparations exhibited identical effects. Low doses of either IgG preparation in combination with subtherapeutic doses of piperacillin significantly enhanced early survival (day 2 for NIgG and day 2 + 3 for Anti-LPS IgG) against P. aeruginosa, but the protective effect waned thereafter. We conclude that a strain-specific antibacterial effect in a compromised mouse infection model can be obtained by early passive immunization with human IgG from large plasma pools. It is suggested that Anti-LPS IgG or NIgG may be of benefit in some cases of gram-negative sepsis when administered as prophylaxis together with proper antibiotic treatment.

MoG: molecular graphics software for the Commodore Amiga

As recently described by Garavelli, the Commodore Amiga 3000 computer is "nearly ideal" for desktop molecular modeling. The chief drawback to date, has been the lack of suitable software. This paper describes a new desktop molecular modeling package, MoG, which is suitable for both research and educational use. The speed of the Amiga 3000 means that MoG competes very favorably with software on IBM-PC machines, and its graphics capabilities allow excellent space-filling representations. The availability of cheap software-compatible home-computer versions of the Amiga places interactive molecular graphics within the reach of many senior high-school students, undergraduates and graduate students.

New application of silane coupling agents for covalently binding antibodies to glass and cellulose solid supports

Bifunctional silane reagents (3-iodopropyl)trimethoxysilane (1), (gamma-glycidoxypropyl)trimethoxysilane (2), and [1-(trimethoxysilyl)-2-(m- (or p-)chloromethyl)phenyl]ethane (3) were used to covalently link goat anti-mouse (GAM) antibodies (Ab) to glass microbeads and cuprammonium rayon hollow-fiber dialyzers. An average of 0.79 and 0.83 microgram of GAM Ab/cm2 was immobilized on the hollow-fiber dialyzers and the glass beads, respectively. The antibodies immobilized on glass microbeads or on hollow-fiber dialyzers were then used to selectively deplete CD34+ cells or CD4+ peripheral blood mononuclear cells (PBMC), respectively. Glass microbeads depleted 80% CD34+ cells with good selectivity, and the hollow-fiber dialyzers depleted an average of 81% CD4+ PBMC.

X-ray structures of the antigen-binding domains from three variants of humanized anti-p185HER2 antibody 4D5 and comparison with molecular modeling

The X-ray structures of 1 Fv and 2 Fab humanized anti-p185HER2 antibody fragments (IgG1-kappa) have been determined at a resolution between 2.7 A and 2.2 A. The antibodies are three different versions of a human antibody framework onto which the antigen recognition loops from a murine antibody (4D5) have been grafted. The sequences of the three versions differ in the framework region at positions L55, H78 and H102. The version 8 Fv fragment crystallizes in space group P2(1) with cell parameters a = 37.6 A, b = 63.4 A, c = 90.2 A, beta = 98.2 degrees, with two molecules per asymmetric unit, and has been refined against data 10.0 A-2.2 A to an R-factor of 18.3%. Versions 4 and 7 Fabs crystallize in space group P1 with cell parameters a = 39.2 A, b = 80.2 A, c = 86.1 A, alpha = 113.1 degrees, beta = 92.7 A, gamma = 102.6 A and two molecules per asymmetric unit. Version 4 has been refined against data 10.0 A-2.5 A resolution to an R-factor of 17.9%. Version 7 has been refined against data 10 A-2.7 A to an R-factor of 17.1%. The X-ray structures have been used to assess the accuracy of structural predictions made via molecular modeling, and they confirm the structural role of certain framework residues and the conformations of five of six complementarity determining regions (CDRS). The average deviation of the model from the X-ray structures is within the range observed among the X-ray structures for 81% of the C alpha atoms. Of the hydrogen bonds common to the X-ray structures, 94% of the main-chain-main-chain and 79% of the main-chain-side-chain ones were predicted by the model. The side-chain conformation was predicted correctly for 79% of the buried residues. The third CDR in the heavy chain is variable, differing by up to 8 A between molecules within an asymmetric unit. The structural relationship between variable domains of light and heavy chains is not significantly altered by the absence of constant domains in the Fv molecule. The antigen-binding potential of an unusual light chain sequence has been confirmed. The arginine at position 66 interacts with the first light chain CDR, but in a fashion somewhat different than predicted. A substitution of a leucine for an alanine side-chain directed between the beta-sheets has only relatively small and local effects.(ABSTRACT TRUNCATED AT 400 WORDS)

Characterization of an antibody to the cross-reacting determinant of the glycosyl-phosphatidylinositol anchor of human membrane dipeptidase

A polyclonal antiserum raised to the phospholipase C-solubilized form of membrane dipeptidase (EC 3.4.13.11) purified from human kidney was found to cross-react with unrelated trypanosomal and porcine glycosyl-phosphatidylinositol anchored proteins. Those antibodies recognising the cross-reacting determinant (CRD) were isolated by chromatography on a column of immobilized phospholipase C-solubilized porcine aminopeptidase P (EC 3.4.11.9), and the epitopes involved in the recognition were then characterized by immunoelectrophoretic blot analysis and by a competitive ELISA. The phospholipase C-solubilized forms of human and porcine membrane dipeptidase, porcine aminopeptidase P and trypanosome variant surface glycoprotein were recognised by the anti-CRD antiserum, and this recognition was abolished by prior treatment of the proteins with either mild acid or nitrous acid. In contrast, the detergent-solubilized, membrane-forms of human and porcine membrane dipeptidase were not recognised. Of a range of components of the glycosyl-phosphatidylinositol anchor, only inositol 1,2-cyclic monophosphate and the insulin-mimetic disaccharide, glucosaminyl-1,6-inositol 1,2-cyclic monophosphate, inhibited in the micromolar range the binding of the anti-CRD antiserum to immobilized porcine aminopeptidase P. These results indicate that the major epitope recognised by this anti-CRD antiserum is the inositol 1,2-cyclic monophosphate formed on phospholipase C cleavage of the glycosyl-phosphatidylinositol anchor.

Antigenicity and immunogenicity of antigenized antibodies. Studies on B and T cells

This laboratory has been testing the possibility of using the complementarity-determining region (CDR) loops of the antibody molecule to express oligopeptide epitopes in an immunologically-accessible and conformationally-suitable way. The new process consists in grafting peptides epitopes derived from antigens other than immunoglobulins into antibody CDR loops. This process, "antibody antigenization," utilizes the immunoglobulin fold as a scaffold to immobilize and present oligopeptide epitopes to the immune system as the integral part of the immunoglobulin molecule. Here we describe some of the initial results with antigenized antibodies (AgAbs).

Practical suggestions for successful immunoenzyme double-staining experiments

Many methodologies exist to perform an immunoenzyme double staining. Hence, the practical problem arises as to which of these methods is optimal for one's own experimental design. A process of selection is described which is derived from our own practical experience. First, a general strategy is outlined for the handling of tissue sections to be used for multiple staining methods. Secondly, the selection of an appropriate immunoenzyme double-staining concept is made using a flow chart. Thereafter we give criteria for the definitive selection of an immunoenzyme double-staining protocol based on the characteristics of the tissue or cell type under study. Particular attention is given to the selection of appropriate detection systems, applying enzymes or gold particles, and good contrasting colour combinations. The problems of visualizing co-localization using immunoenzyme double staining are dealt with, and suggestions are made to adapt the method, if necessary, in order to optimize it.

The prediction and characterization of metal binding sites in proteins

The rational engineering of novel functions into proteins can only be attempted when the underlying structural scaffold on which the new function is displayed and the structure of the target protein are both well understood. To introduce functions mediated by metals it is therefore necessary to identify the principal liganding residues for the chosen metal, the required architecture of the metal-ligand complex and sites within the target protein that could accommodate such sites. Here we present a method that applies structural information from the protein data bank to the ab initio design and characterization of novel metal binding sites. The prediction method has been tested on 28 metalloprotein structures from the Brookhaven Protein Data Bank. It successfully identified > 90% of the metal binding sites. In addition, we have used the method to design and characterize zinc binding sites in two antibody structures. Metal binding studies on one of these putative metalloantibodies showed metal binding, confirming the predictive power of the method.

Production and characterization of antibodies directed against organophosphorus nerve agent VX

A strategy is described to raise high-affinity antibodies directed against the organophosphorus nerve agent VX [O-ethyl S-(2-diisopropylamino)ethyl)methyl phosponothionate]. Ten chemical derivatives of VX (haptens) have been synthesized. Their structures differ principally from VX structure by substitution of S-atom by an O-atom or CH2-group and by introduction of a reactive group (carboxylic acid, arylamine or primary amine) on the O-ethyl side chain. None of these haptens, except one, exhibit potential toxicity as tested by their inhability to inhibit acetylcholinesterase (E.C. 3.1.1.7.). After coupling with a protein carrier, they were injected intradermally to rabbits. Nine of these immunogenic conjugates led to the appearance of antibodies able to bind VX in a competitive solid phase immunoassay. The apparent titer and affinity of the antisera differed greatly depending on the hapten used. The highest affinity (9 nM) was observed with the VX derivative bearing O-S substitution and O-ethyl-carboxylic side chains. The antibodies appear specific for VX, since cross-reactivity with other nerve agents (Soman, Sarin or Tabun) was low. However, two haptens elicited antibodies with affinity to Soman or Sarin in the micromolar range. Antibodies were able to neutralize VX inhibition of acetylcholinesterase in vitro but not in vivo.

Epitope mapping with ELISA of an antibody against oxytocin used for the characterization of an oxytocin-like epitope in the sex segmental ganglia of the leech Erpobdella octoculata

1. Using direct, inhibiting and competitive enzyme-linked immunosorbent assay (ELISA), two steps were involved in the mapping of the recognition site of a polyclonal antibody against oxytocin (OT). 2. The percentage of cross-reactivity between OT and the N-terminal or the C-terminal fragment of OT demonstrated that the C-terminal fragment is the antigenic part of OT. 3. The percentage of cross-reactivity between OT and other molecules of the OT family indicated that the amino acid in the 8-position and the C-terminal amide of the OT molecule contribute to the recognition. 4. In the two sex segmental ganglia of the leech Erpobdella octoculata, where cells immunoreactive to the anti-OT are detected, the antibody has allowed to characterize an epitope close to the mammalian OT by its C-terminal part.

Glomerular C3c localization indicates ongoing immune deposit formation and complement activation in experimental glomerulonephritis

In antibody-mediated glomerular disease, deposits of C3 (C3b) are common and are degraded by factor I to C3c and C3d. However, the kinetics of C3b degradation in glomerulonephritis have not been defined. To do this, we studied three models of complement-dependent glomerulonephritis with established C3 deposits (passive Heymann nephritis, cationized immunoglobulin G membranous nephropathy, and concanavalin A-anticoncanavalin A glomerulonephritis). C3b deposition was halted by administration of cobra venom factor, and the disappearance of C3c and C3d from glomeruli was measured with specific antibodies and quantitative fluorescence densitometry. Results showed that C3c deposits were reduced by over 85% within 24 hours in all three models. C3c clearance was unaffected by site or mechanism of deposit formation. C3d deposits persisted despite lack of ongoing complement activation. In passive Heymann nephritis when disease activity was monitored by urinary C5b-9 excretion, C3c was cleared in parallel with return of urine C5b-9 excretion to normal values. We conclude that glomerular deposits of C3c are cleared within 24 hours of cessation of complement activation. Positive staining for C3 utilizing antibody specific for the C3c portion documents recent complement activation usually reflecting new immune deposit formation.

Antibodies to SPARC inhibit albumin binding to SPARC, gp60, and microvascular endothelium

Albumin, through its binding to the endothelial glycocalyx, functions as a major determinant of capillary permeability and as a carrier for various small molecules in its transcytosis across continuous endothelium via plasma-lemmal vesicles. Several albumin-binding proteins (ABP) have been identified: three membrane-associated ABP, which we call gp60, gp30, and gp18, and one secreted protein, acidic and rich in cysteine (SPARC). In this study, we used antiserum raised against bovine SPARC (BON) to investigate the possible interrelationships among ABP to better understand their role in binding and transcytosis. BON not only interacted with SPARC secreted by cultured endothelium but also recognized gp60 in lysates of cultured rat, human, and bovine endothelial cells. Purified SPARC inhibited BON interaction with gp60. BON immunoglobulin (Ig)G specifically inhibited albumin binding to both SPARC and gp60 extracts. This effect was eliminated by preabsorption of BON to immobilized SPARC. BON also significantly inhibited albumin binding to cultured microvascular endothelial cells via its interaction with gp60. Anti-SPARC peptide sera were also tested, and one serum raised against a peptide encompassing an NH2-terminal region of SPARC recognized both SPARC and gp60 but did not inhibit albumin binding; gp30 and gp18 were not recognized by any of these anti-SPARC antibodies. These results suggest that SPARC and gp60 are functionally and immunologically related ABP that may share a common albumin-binding domain. gp60 appears to be the major mediator of albumin binding to microvascular endothelium.

Characterization of human 1,25-dihydroxyvitamin D3 receptor anti-peptide antibodies

Rabbit and chicken antibodies were raised against two peptides synthesized according to the structure of human 1,25-dihydroxyvitamin D3 receptor (hVDR): rabbit alpha hVDR-103 against the N-terminal amino acids 5-18 and alpha hVDR-104 against the amino acids 172-186 in the hinge region and chicken alpha hVDR-cab11 against the amino acids 172-186, respectively. The specificity of the antibodies was tested by peptide saturation, SDS-PAGE immunoblotting, gel shift assay and sucrose gradient centrifugation. Immunoblotting of a soluble extract (cytosol) from osteosarcoma cell line MG-63 showed a single band with an M(r) of about 48,000 and human intestine cytosol a broad band (50-63,000) for both antibodies. The antibodies recognized activated (3.2S) hVDR by shifting the centrifugation sedimentation profile to 5-6S. The antibodies showed nuclear immunostaining of unoccupied VDR in human osteosarcoma cells MG-63, U2-Os and SaOs-2. The immunoreaction could be saturated with the corresponding synthetic peptide. In immunoblot alpha hVDR-103 reacted with human and rat VDR, whereas alpha hVDR-104 recognized human VDR only. Similarly in immunohistochemistry, alpha hVDR-103 showed staining with hVDR and rVDR, whereas alpha hVDR-104 reacted only with hVDR. All antibodies recognized the native hVDR as verified with sucrose gradient centrifugation or immunoprecipitation but only alpha hVDR-103 and alpha hVDR-cab11 in gel shift assay of hVDR associated with the vitamin D-responsive element of human osteocalcin gene promoter.

Modeling the anti-CEA antibody combining site by homology and conformational search

A model for an antibody specific for the carcinoembryonic antigen (CEA) has been constructed using a method which combines the concept of canonical structures with conformational search. A conformational search technique is introduced which couples random generation of backbone loop conformations to a simulated annealing method for assigning side chain conformations. This technique was used both to verify conformations selected from the set of known canonical structures and to explore conformations available to the H3 loop in CEA ab initio. Canonical structures are not available for H3 due to its variability in length, sequence, and observed conformation in known antibody structures. Analysis of the results of conformational search resulted in three equally probable conformations for H3 loop in CEA. Force field energies, solvation free energies, exposure of charged residues and burial of hydrophobic residues, and packing of hydrophobic residues at the base of the loop were used as selection criteria. The existence of three equally plausible structures may reflect the high degree of flexibility expected for an exposed loop of this length. The nature of the combining site and features which could be important to interaction with antigen are discussed.

Engineered antibodies as pharmacological tools

The ability to engineer the antibody molecule has now progressed to the stage where one can realistically contemplate creating a pharmacologically useful targeting molecule comprising a single-chain, minimal antibody combining site together with a domain that imparts a second functionality. It will certainly be possible in the near future to adjust the fine specificity and affinity of the antibody domain, either by in vitro selection methods or by site-directed mutagenesis based on structural criteria. The functional domain could be an enzyme, a toxin, or any other protein that suits a pharmacological purpose. In this review I have illustrated these directions primarily by summarizing work from my laboratory and those of my collaborators. The review covers single point mutations in the heavy chains of digoxin-specific antibodies that either strikingly diminish or strikingly enhance recognition of a small feature of the antigen, the position 12 OH moiety in the steroid nucleus. The principles for constructing a minimal, single-chain antigen-binding domain based on one of the digoxin-specific antibodies are also outlined, as are the principles for incorporating such domains into fusion proteins. Finally, as a practical application of antibody-targeted enzymes, the construction and evaluation of an anti-fibrin antibody-single-chain urokinase fusion protein is examined. This protein has enhanced potency and specificity both in vivo and in vitro, and it offers the promise of increased therapeutic efficacy as well as diminished toxicity.

Combinatorial functions of two chimeric antibodies directed to human CD4 and one directed to the alpha-chain of the human interleukin-2 receptor

The general feasibility of chimerization of monoclonal antibodies (mAbs) has already been shown for a large number of them. In order to evaluate in vitro parameters relevant to immunosuppressive therapy, we have chimerized and synthesized two anti-CD4 mAbs recognizing two different epitopes on the human T-lymphocyte antigen, CD4. The chimerized mAbs are produced at levels corresponding to those of the original hybridoma cell lines. With respect to activation of human complement, the individual Abs are negative; however, when used in combination, complement activation was performed. When applied in combination, they were found to modulate the CD4 antigen, whereas the individual mAb do not display this property. Individually they mediate an up to 60% inhibition of the mixed lymphocyte reaction (MLR). However, by combination of an anti-CD4 mAb with one directed against the alpha-chain of the human IL2 receptor, nearly 100% inhibition of the MLR was achieved, even with reduced dosage of the mAbs. Our data suggest that the combination of an anti-CD4 mAb and an anti-IL2R alpha chain mAb is more effective with respect to immunosuppression than each mAb by itself, indicating that this mAb cocktail could be a new strategy for immunosuppressive therapy.

Immunological detection of nitric oxide synthase(s) in human tissues using heterologous antibodies suggesting different isoforms

Nitric oxide (NO) is generated from L-arginine by NO synthases. Localization of the brain enzyme has been carried out in the rat; however, despite data suggesting that NO is a major regulator of vascular and neural functions in man, there is no information about the localization of NO synthase in human tissues. Rabbit antisera to NO synthase purified from rat brain (antisera A and B) were raised, tested by Western blotting, affinity purification and enzyme immunoprecipitation assay, and used to investigate the distribution of the enzyme in a variety of human tissues by immunohistochemistry. Antisera to two synthetic peptides from cloned neural NO synthase were used to aid specificity testing. Anti-sera A and B reacted with a approximately 160-kDa protein in Western blots of human brain extracts, gave immunostaining of nerves, and precipitated enzyme activity from rat brain homogenates. Antiserum B to NO synthase also reacted with proteins of M(r) between 125 and 140 kDa in extracts of well-vascularised tissues, and immunostained vascular endothelium; the neural and vascular immunoreactivity persisted after affinity purification of antiserum B with the approximately 160 kDa protein. Endothelial staining with antiserum B was seen in respiratory tract, liver, skin and umbilicus; syncytial trophoblasts stained in the placenta. Neural staining with antiserum A and B was seen in the myenteric and submucous plexus, and in nerve fibres in smooth muscle of the gut and in many areas of the central nervous system, particularly cortex, hippocampus, hypothalamus, cerebellum, brain stem and spinal cord.(ABSTRACT TRUNCATED AT 250 WORDS)

Versatility of anti-horseradish peroxidase antibody-gold complexes for cytochemistry and in situ hybridization: preparation and application of soluble complexes with streptavidin-peroxidase conjugates and biotinylated antibodies

In previous studies we have employed a gold-labelled, affinity-purified polyclonal antibody against horseradish peroxidase (anti-HRP--gold) in the avidin-biotin peroxidase complex (ABC) technique and indirect labelled avidin-biotin methods. The gold-labelled antibody was used as final revealing reagent to replace the 3,3'-diaminobenzidine (DAB) reaction by immunogold silver staining. The anti-HRP--gold reagent proved to be advantageous since blocking of endogenous peroxidase activity in the tissue sections was not further required and staining of superior contrast and resolution could be achieved in paraffin sections. In the present study we have optimized this technique by combining the last two incubation steps, i.e. HRP-conjugated streptavidin and anti-HRP--gold. Different ratios of the two reagents were tested empirically to establish the conditions for the formation of a soluble complex with optimal staining properties. Quantitative evaluation by densitometry of the staining intensity showed that the soluble streptavidin-HRP/anti-HRP--gold complex and the indirect labelled avidin-biotin method employing the gold-labelled anti-HRP antibody performed equally well. Thus, the availability of this complex simplifies the streptavidin-biotin immunogold technique for immunohistochemistry, lectin histochemistry and in situ hybridization and further demonstrates the versatility of anti-HRP--gold complexes.

Dissection of the combining site in a humanized anti-Tac antibody

The genetically engineered "humanized" anti-Tac antibody (HAT) has been shown to bind the p55 chain of the human IL-2R with an affinity close to that of the murine anti-Tac. Although the HAT molecule contains all six mouse CDR, it was not known which, and to what extent, each of the CDR contributes to Ag binding. These questions were addressed by constructing a series of variant HAT antibodies, each substituting a single HAT CDR with a heterologous CDR. The association constants of the variant HAT antibodies to p55 were determined by competitive binding analysis. We find that CDR 1 and 3 of the H chain and CDR 3 of the L chain are essential for maintaining binding. The remaining three CDR appear to be involved to a lesser degree.

Rapid affinity-purification and biotinylation of antibodies

A simple and rapid method to affinity-purify and biotinylate antibodies was developed. The method utilizes separation of antigens by sodium dodecyl sulfate polyacrylamide gel electrophoresis, followed by transfer to nitrocellulose and binding of the antibodies to the specific antigen. The antibodies are biotinylated, while still bound to the antigen, thus avoiding the conjugation of the active antigen-binding sites of the antibodies. These antibodies have been successfully used in double-label immunofluorescence studies, but they should be likewise applicable in other immunological protocols.

Development and applications of a radioimmunoassay (RIA) for the in vitro and in vivo quantification of murine IL-1 beta

A specific, precise, and accurate radioimmunoassay (RIA) for murine interleukin-1 beta (mIL-1 beta), with a sensitivity of 250 pg/ml, has been established. Although mIL-1 beta shares structural homology and multiple biological properties with mIL-1 alpha, this RIA did not detect mIL-1 alpha or other murine cytokines such as TNF and IL-6. Recombinant mIL-1 beta, freshly added in different concentrations to murine plasma, was recovered from 88 to 104%, and intra- and interassay coefficients of variation never exceeded the 10% value. Parallel analysis showed that murine plasma and cell or organ supernatants did not affect the test. This characteristic allowed mIL-1 beta analysis directly in the nonmanipulated biological specimens. In murine macrophage supernatants collected after 24 h of in vitro stimulation with LPS, nanogram fractions of IL-1 beta were detected by RIA. These values corresponded to approximately 50% of the total IL-1 detected by the LAF bioassay. In spleen, liver, and lung, IL-1 beta appeared at significant levels (110 ng/g of lung, 638 ng/g of spleen, and 78 ng/g of liver) as early as 1 h after LPS administration, reached the plateau 1-2 h later, and then slowly but progressively decreased. In plasma and brain, nanogram fractions of IL-1 beta were detectable by 4 h post-LPS. Thereafter, IL-1 beta levels progressively increased to reach the value of 44 ng/g in the brain and 2 ng/ml in plasma 8 h after LPS treatment.

Reversible immobilization of antibodies on magnetic beads

A streptavidin-biotin system was utilized to prepare an antibody-polyadenylic acid conjugate which was subsequently attached to commercially available magnetic beads, Dynabeads oligo(dT)25. Biotinylated polyadenylic acid was combined with streptavidin and the resulting polyadenylic acid-streptavidin was conjugated with an antibody-biotin derivative. The immobilized antibody-polyadenylic acid conjugate was separated from the reaction mixture by hybridization with complementary oligonucleotide immobilized on the surface of Dynabeads oligo(dT)25. The immobilized antibody-polyadenylic acid can be released from the carrier, utilizing low-ionic-strength buffers. The system is intended to be utilized in cell sorting, using immobilized antibodies against cell surface antigens. Dissociation of antibody-containing conjugate from magnetic beads is essential for the isolation of viable cells via positive cell sorting.

Characterization of anti-interferon-alpha antibodies appearing during recombinant interferon-alpha 2a treatment

Patients with malignant midgut carcinoid tumours received recombinant interferon-alpha 2a (rIFN-alpha 2a) or rIFN-alpha 2a and chemotherapy (streptozocin and doxorubicin) for 6 months, and then rIFN-alpha 2a alone. Antibodies, mainly of IgG type, binding to rIFN-alpha 2a developed in nine of 22 patients (41%), as determined by immunoassay. In seven patients, antibodies also neutralized the biologic (anti-viral) activity of rIFN-alpha 2a. Anti-IFN-alpha 2a antibodies were equally frequent in both sexes and treatment groups, but were not observed in those patients (n = 8) that had previously received other types of IFN. Antibodies appeared after a median of 6 months of rIFN-alpha 2a treatment and had a median duration of 6 months. The anti-IFN-alpha 2a antibody titres declined with time with no obvious relation to change of therapy, also during continued IFN-alpha 2a treatment. High titres of neutralizing antibodies appeared to impair anti-tumoural effects in individual potential responders. Anti-IFN-alpha 2a antibodies further examined in six patients bound to native IFN-alpha subtypes present in both allogenic and autologous leucocyte IFN-alpha. Such autoantibodies neutralized the biologic activity of autologous IFN-alpha in two patients, and in a third were partially neutralizing.

Preparation and characterization of an antibody specific to the rat dopamine D2 receptor

Antibodies specific to the dopamine D2 receptor have been raised in rabbits using synthetic peptides. The resulting antiserum was sensitive to picogram quantities of peptide as measured by enzyme-linked immunoassay and was shown to have a 33% cross-reactivity with partially purified D2 receptor protein. No detectable cross-reactivity with similarly prepared fungal membranes was observed. D2 receptor preparations from normal rat pituitary cells were used in Western blot analysis. Bands of M(r) = 95,000 and 34,000 were detected in these preparations with a third faint band at 120,000. These correspond to the pituitary D2 receptor.

Radioimmunocytochemical localization of corticotropin-releasing factor and adrenocorticotropin in the hypothalamo-hypophyseal system of the rat: effects of adrenalectomy

Various radioimmunocytochemical approaches have been utilized to localize primary antibody-antigen complexes. Here we examined the binding properties of three different radioiodinated compounds for their ability to label the antibody-antigen complex, including: donkey anti-rabbit immunoglobulin, donkey anti-rabbit F(ab')2-IgG, and a biotinylated goat anti-rabbit secondary antibody followed by [125I]-avidin. These probes were used to localize rabbit primary antisera against corticotropin-releasing factor (CRF) and adrenocorticotropin-releasing hormone (ACTH) in the hypothalamo-hypophyseal system of the rat. The pattern of labeling with each radiolabeled probe was consistent with the light microscopic immunocytochemical staining for CRF and ACTH. The utility of the radioimmunocytochemical method for quantitative analyses was further tested by studying the effects of adrenalectomy (ADX) on the levels of immunoreactive CRF and ACTH in the hypothalamo-hypophyseal system. Computer-assisted microdensitometric analysis of immunoreactive CRF levels in the median eminence indicated that there was a 33% decrease 24 h after ADX. Immunoreactive ACTH levels in the anterior pituitary were significantly decreased from 1 day (38%) to 1 week (36%) after ADX and were increased at 2 weeks (89%). The changes in CRF and ACTH levels, as measured radioimmunocytochemically after ADX, were consistent with previous biochemical studies. These results indicate that computer-assisted radioimmunocytochemical analysis can be used quantitatively to measure immunoreactivity in tissue sections. The high resolution and high sensitivity provided by this method should make it widely applicable.