Recombinant β-Glucocerebrosidase specific immunoaffinity ligands selected from phage-displayed combinatorial scFv libraries

Antibodies specific to β-Glucocerebrosidase were selected from phage displayed naïve scFv libraries. Biopannings were performed against recombinant human protein β-Glucocerebrosidase immobilized on polystyrene surface, specific phages were eluted with 50% ethylene glycol in citrate buffer (pH 6.0). Several specific binders were discovered and converted to full-size hIgG1 antibodies leading to highly stable binders with dissociation constants (Kd) in the range 10-40 nM. The antibodies were used further as ligands for affinity chromatography, where efficient and selective recovery of biologically active β-Glucocerebrosidase from cultured media of Chinese hamster ovary cells was demonstrated. β-Glucocerebrosidase was purified to nearly homogeneous state and had specific activity comparable to the commercially available preparations (40-44 U/mg protein). The obtained immunoaffinity sorbents have high capacity and can be easily regenerated.

Enzymes as Immunotherapeutics

Enzymes are attractive as immunotherapeutics because they can catalyze shifts in the local availability of immunostimulatory and immunosuppressive signals. Clinical success of enzyme immunotherapeutics frequently hinges upon achieving sustained biocatalysis over relevant time scales. The time scale and location of biocatalysis are often dictated by the location of the substrate. For example, therapeutic enzymes that convert substrates distributed systemically are typically designed to have a long half-life in circulation, whereas enzymes that convert substrates localized to a specific tissue or cell population can be more effective when designed to accumulate at the target site. This Topical Review surveys approaches to improve enzyme immunotherapeutic efficacy via chemical modification, encapsulation, and immobilization that increases enzyme accumulation at target sites or extends enzyme half-life in circulation. Examples provided illustrate "replacement therapies" to restore deficient enzyme function, as well as "enhancement therapies" that augment native enzyme function via supraphysiologic doses. Existing FDA-approved enzyme immunotherapies are highlighted, followed by discussion of emerging experimental strategies such as those designed to enhance antitumor immunity or resolve inflammation.

[New bioaffine sorbents for selective elimination of autoantibodies against human thyroperoxidase in autoimmune thyroid diseases]

New bioaffine sorbents containing bioselective ligand, synthetic analog of the human thyroperoxidase antigenic determinant--tetrapeptide H-Glu-Gln-betaAla-Lys-OMe, immobilized on two polymeric matrixes--a polyacrylamide gel and CNBr-activated sepharose 4B were synthesized. The offered immunosorbents were shown have high selectivity in relation to autoantibodies against thyroperoxidase and can find an application for medicine and experimental biochemistry for selective elimination of autoantibodies from serum or plasma of the patients suffering from autoimmune thyroid diseases.

Enzyme stabilization via cross-linked enzyme aggregates

Extensive cross-linking of a precipitate of a protein by a cross-linking reagent (glutaraldehyde has been most commonly used) creates an insoluble enzyme preparation called cross-linked enzyme aggregates (CLEAs). CLEAs show high stability and performance in both conventional aqueous media as well as nonaqueous media. These are also stable at fairly high temperatures. CLEAs having more than one kind of enzyme activity can be prepared and such CLEAs are called combi-CLEAs or multipurpose CLEAs. Extent of cross-linking often influences their morphology, stability, activity, and enantioselectivity.

Characterisation of peptide microarrays for studying antibody-antigen binding using surface plasmon resonance imagery

Background

Non-specific binding to biosensor surfaces is a major obstacle to quantitative analysis of selective retention of analytes at immobilized target molecules. Although a range of chemical antifouling monolayers has been developed to address this problem, many macromolecular interactions still remain refractory to analysis due to the prevalent high degree of non-specific binding. We describe how we use the dynamic process of the formation of self assembling monolayers and optimise physical and chemical properties thus reducing considerably non-specific binding and allowing analysis of specific binding of analytes to immobilized target molecules.

Methodology/Principal Findings

We illustrate this approach by the production of specific protein arrays for the analysis of interactions between the 65kDa isoform of human glutamate decarboxylase (GAD65) and a human monoclonal antibody. Our data illustrate that we have effectively eliminated non-specific interactions with the surface containing the immobilised GAD65 molecules. The findings have several implications. First, this approach obviates the dubious process of background subtraction and gives access to more accurate kinetic and equilibrium values that are no longer contaminated by multiphase non-specific binding. Second, an enhanced signal to noise ratio increases not only the sensitivity but also confidence in the use of SPR to generate kinetic constants that may then be inserted into van't Hoff type analyses to provide comparative ΔG, ΔS and ΔH values, making this an efficient, rapid and competitive alternative to ITC measurements used in drug and macromolecular-interaction mechanistic studies. Third, the accuracy of the measurements allows the application of more intricate interaction models than simple Langmuir monophasic binding.

Conclusions

The detection and measurement of antibody binding by the type 1 diabetes autoantigen GAD65 represents an example of an antibody-antigen interaction where good structural, mechanistic and immunological data are available. Using SPRi we were able to characterise the kinetics of the interaction in greater detail than ELISA/RIA methods. Furthermore, our data indicate that SPRi is well suited to a multiplexed immunoassay using GAD65 proteins, and may be applicable to other biomarkers.

Electrochemical immunosensor of tumor necrosis factor α based on alkaline phosphatase functionalized nanospheres

A novel immunosensor for sensitive detection of tumor necrosis factor α was reported. First of all, gold nanoparticles were uniformly assembled on the surface of poly (styrene-acrylic acid) nanospheres, which was used as the matrix to conjugate alkaline phosphatase (ALP). And then, the obtained composite was used as multi-enzyme functionalized label for immunoassay. Biocompatible polyaniline doped with poly (acrylic acid) was electro-polymerized at the glass carbon electrode to construct the matrix for the immobilization of antibody TNF-α. After the sandwich immunoreaction, the labeled ALP was used to hydrolyze α-naphthyl phosphate to produce the electroactive α-naphthol, which could be amperometrically detected. The results showed that the electrochemical signals were proportional to the logarithm of the antigen concentration in the range of 0.02-200.00 ng/mL with the detection limit of 0.01 ng/mL. The developed immunoassay showed high sensitivity, acceptable stability and reproducibility, which might have potentially broad applications in protein diagnostics and bioassay.

[Prospects for using antigenic nanosystems in the diagnosis and treatment of inflammatory rheumatic diseases]

AIM

To study whether immobilized antigenic nanosystems (ANS) may be designed on the basis of antigens of varying chemical nature to identify and to remove specific antibodies (Ab) from the blood of patients with systemic lupus erythematosus (SLE).

SUBJECTS AND METHODS

Sixty patients with the diagnosis of SLE verified by the 1997 American College of Rheumatology criteria and 30 apparently healthy individuals were followed up. The levels of Ab to catalase (Cat), xanthine oxidase (XO), and cardiolipin (CL) were measured by enzyme immunoassay, by applying the respective ANS as an antigenic matrix.

RESULTS

There was a significant relationship of the levels of Ab to Cat and XO to the activity of SLE. It was shown that Ab to Cat and XO could affect the functional activity of serum enzymes. The level of Ab to CL in patients with SLE was found to depend on two parameters - the intensity of the disease and the presence of antiphospholipid syndrome; acute cerebral circulatory disorder and thrombocytopenia were observed to have a significant unidirectional impact on the level of Ab to CL. Immobilized CL-based ANSs were effective in eliminating Ab to CL from the whole blood of patients with SLE, without resulting in a significant hemolysis of blood corpuscles and in a reduction of total protein concentrations.

CONCLUSION

The development and introduction of preventive methods for the early diagnosis of SLE may be extended, by using ANS based on Cat, XO, and CL antigen. The designing and putting into practice novel ANS-based hemosorbents may allow immunosorption to occupy a prominent place in the pathogenetic therapy of inflammatory autoimmune diseases.

Detection of Polyclonal Antibody Against Any Area of the Protein-Antigen Using Immobilized Protein-Antigens: The Critical Role of the Immobilization Protocol

Antigens immobilized on solid supports may be used to detect or purify their corresponding antibodies (Ab) from serum. Direct immobilization of antigens on support surfaces (through short spacer arms) may promote interesting stabilizing effects on the immobilized antigen. However, the proximity of the support may prevent the interaction of some fractions of polyclonal Ab with some regions of the antigen (those placed in close contact with the support surface). Horseradish peroxidase (HRP) was immobilized on agarose by different protocols of multipoint covalent immobilization involving different regions of the antigen surface. Glyoxyl-agarose, BrCN-agarose, and glutaraldehyde-agarose were used as activated supports. Each HRP-immobilized preparation was much more stable than the soluble enzyme, but it was only able to adsorb up to 60-70% of a mixture of polyclonal anti-HRP antibodies. On the other hand, HRP was also immobilized on agarose through a very long, flexible, and hydrophilic spacer arm (dextran). This immobilized HRP was hardly stabilized, but it was able to adsorb 100% of the polyclonal anti-HRP. The absence of steric hindrances seems to play a critical role favoring the complete recognition of all classes of polyclonal Ab. Another solution to achieve a complete adsorption of polyclonal Ab on immobilized-stabilized antigens has been also reached by using a mixture of the differently immobilized and stabilized HRP-agarose preparations. In this case, an improved storage and operational stabilities of the immobilized antigens can be combined with the complete adsorption of any class of antibody.

Detection of enzymatic activity by means of a diffraction-based biosensor

We demonstrate here, for the first time, the capability of a diffraction-based sensor to detect enzyme activity and provide a simple measure of enzyme kinetics. Patterned samples of mouse IgG were exposed to the enzyme trypsin and the progress of enzymatic degradation of IgG was followed by measuring the decrease in diffraction signal intensity as a function of time. The diffraction signal intensity decreased exponentially as a function of time over a range of trypsin concentrations from 2-100 microg mL(-1). Atomic-force microscope images of the samples before and after exposure to trypsin show that the thickness of patterned protein is greatly reduced by the enzyme action, providing useful insight into the mechanism of signal change for the diffraction sensor.

A new assay format for electrochemical immunosensors: polyelectrolyte-based separation on membrane carriers combined with detection of peroxidase activity by pH-sensitive field-effect transistor

A new rapid immunotechnique combining separation of reactants by filtration through a porous membrane and potentiometric detection of the bound enzyme label by a pH-sensitive field-effect transistor is proposed. The complexes to be detected are formed by the method described earlier in (Anal. Chem. 71 (1999) 3538), including a homogeneous binding of immunoreactants and a polyanion carrier (polymethacrylate) followed by heterogeneous separation on a membrane incorporating an immobilized polycation (poly-N-vinyl-4-ethylpyridinium). The proposed technique for a sensitive detection of peroxidase label is based on the measurement of pH changes in the optimised substrate solution containing o-phenylenediamine, hydrogen peroxide and ascorbic acid. The antigens studied were herbicide atrazine and hormone testosterone. Their specific detection is realised via competitive binding of free and peroxidase-labelled antigens by antibodies integrating with a (staphylococcal protein A-polyanion) conjugate. The total analysis time is 20-25 min. The range of quantitative detection is 0.2-100 ng ml(-1) for atrazine and 5-300 ng ml(-1) for testosterone. Data scatter of replicate tests varies from 3 to 10%. Application of protein A-polyanion conjugate allows to use the proposed protocol for different antigens without additional treatment of specific antisera.

Preparation of a highly stable, very active and high-yield multilayered assembly of glucose oxidase using carbohydrate-specific polyclonal antibodies

The purified oligosaccharide chains of Aspergillus niger glucose oxidase were coupled to BSA with the help of the cross-linking reagent glutaraldehyde. The neoglycoconjugate thus obtained was purified by concanavalin A-Sepharose chromatography and characterized by SDS/PAGE. Immunization of rabbits with the neoglycoprotein raised the glycosyl-specific anti-(glucose oxidase) polyclonal antibodies. Antibodies were purified by (NH(4))(2)SO(4) precipitation, followed by DEAE-cellulose chromatography. The IgG-Sepharose was prepared by covalently coupling the purified polyclonal antibodies to the CNBr-activated Sepharose 4B. The large assembly of glucose oxidase was made on the IgG-Sepharose by alternate incubation of glucose oxidase and glycosyl-specific anti-(glucose oxidase) polyclonal IgG. The immunoaffinity-layered assembled preparations were highly active and, after six alternate binding cycles with enzyme and glycosyl-specific IgG, the amount of enzyme immobilized could be raised 30-fold. The K (m) value of immunoaffinity-layered glucose oxidase preparations remained unaltered, while the V (max) slightly decreased as compared with the soluble enzyme. A layer-by-layer immobilization of glucose oxidase resulted in significant improvement in stability against high temperature, 4.0 M urea and very high concentrations of water-miscible organic solvents such as acetone, dimethylformamide, dioxan and tetrahydrofuran.

Immobilized earthworm fibrinolytic enzyme III-1 with carbonyldiimidazole activated-agarose

Earthworm fibrinolytic enzyme III-1 (EFE-III-1) was prepared to couple with cross-linking agarose activated by 1,'-Carbonyl- diimidazole (CDI) in this study. Although the activity of the immobilized protease decreased to approximately 64% of the native enzyme, the activity of EFE-III-1 coupled with the resin activated by CDI was higher than that activated by cyanogen bromide (CNBr). The immobilized protease was experimentally demonstrated to hydrolyze IgG, albumin and creatine kinase, besides fibrin(ogen) and plasmin(ogen), suggesting that EFE had a broad substrate specificity.

B-cell autoepitopes on the acetylcholinesterase-homologous region of human thyroglobulin: association with Graves' disease and thyroid eye disease

OBJECTIVE

Thyroglobulin (Tg) is a large autoantigen involved in autoimmune thyroid diseases. Tg epitopes have, so far, been identified within large peptides. In the present study, we used small synthetic peptides to finely map serological epitopes on the highly immunogenic C-terminal region of Tg. Homology of this region to acetylcholinesterase (AChE) has been implicated in the pathogenesis of thyroid eye disease (TED) through cross-reactive antibodies.

METHODS

We tested total IgG purified from four pilot Graves' disease (GD) sera reactive with both Tg and AChE and from three healthy controls, for reactivity against overlapping 20mer peptides (pin synthesis) covering the sequence 2171-2748 of human Tg. Antibody-reactive peptides were subsequently synthesized by a solid-phase technique for confirmation with a large number of sera: 99 GD, 32 Hashimoto's thyroiditis (HT) and 45 healthy controls.

RESULTS

Peptides TgP15, TgP26 and TgP41 (amino acids 2339-2358, 2471-2490 and 2651-2670 respectively) were found to be targets of autoantibodies on intact Tg, recognized by a statistically significant proportion of GD sera (22.2%, 35.4% and 30.3% respectively), compared with HT (0%, 15.6% and 6.3% respectively) and healthy controls (0%, 4.4% and 4.4% respectively). The majority of GD sera (56.6%) were positive for at least one of the three peptides. In GD, TgP26 reactivity was found to be associated with TED (48.6% with TED versus 25.5% without TED, P<0.05).

CONCLUSION

Some epitopes on the C-terminal region of Tg are associated with GD. A subset of Tg-reactive autoantibodies, directed to this region, is associated with TED and may be involved in the development of the disease.

Development of a robust scintillation proximity assay for protein tyrosine phosphatase 1B using the catalytically inactive (C215S) mutant

Protein tyrosine phosphatases are a class of enzymes that function to modulate tyrosine phosphorylation of cellular proteins and play an essential role in regulating cell function. PTP1B has been implicated in the negative regulation of the insulin signaling pathway by dephosphorylating the activated insulin receptor. Inhibiting this phosphatase and preventing the insulin-receptor downregulation has been suggested as a target for the treatment of Type II diabetes. A high-throughput screen for inhibitors of PTP1B was developed using a scintillation proximity assay (SPA) with GST-- or FLAG--PTP1B((1-320)) and a potent [(3)H]-tripeptide inhibitor. The problem of interference from extraneous oxidizing and alkylating agents which react with the cysteine active-site nucleophile was overcome by the use of the catalytically inactive C215S form of the native enzyme (GST--PTP1B(C215S)). The GST--PTP1B was linked to the protein A scintillation bead via GST antibody. The radiolabeled inhibitor when bound to the enzyme gave a radioactive signal that was competed away by the unknown competitive compounds. Further utility of PTP1B(C215S) was demonstrated by mixing in the same well both the catalytically inactive GST--PTP1B(C215S) and the catalytically active FLAG--CD45 with an inhibitor. Both a binding and kinetic assay was then performed in the same 96-well plate with the inhibition results determined for the PTP1B(C215S) (binding assay) and CD45 (activity assay). In this way inhibitors could be differentiated between the two phosphatases under identical assay conditions in one 96-well assay plate. The use of a mutant to reduce interference in a binding assay and compare with activity assays is also amenable for most cysteine active-site proteases.

Mutations of an epitope hot-spot residue alter rate limiting steps of antigen-antibody protein-protein associations

The antibodies, HyHEL-10 and HyHEL-26 (H10 and H26, respectively), share over 90% sequence homology and recognize with high affinity the same epitope on hen egg white lysozyme (HEL) but differ in degree of cross-reactivity with mutant lysozymes. The binding kinetics, as measured by BIAcore surface plasmon resonance, of monovalent Fab from both Abs (Fab10 and Fab26) to HEL and mutant lysozymes are best described by a two-step association model consistent with an encounter followed by docking that may include conformational changes. In their complexes with HEL, both Abs make the transition to the docked phase rapidly. For H10, the encounter step is rate limiting, whereas docking is also partially rate limiting for H26. The forward rate constants of H10 are higher than those of H26. The docking equilibrium as well as the overall equilibrium constant are also higher for H10 than for H26. Most of the free energy change of association (Delta G degrees) occurs during the encounter phase (Delta G1) of both Abs. H10 derives a greater amount and proportion of free energy change from the docking phase (Delta G2) than does H26. In the H10--HEL(R21Q) complex, a significant slowing of docking results in lowered affinity, a loss of most of Delta G2, and apparently faster dissociation. Slower encounter and docking cause lowered affinity and a loss of free energy change primarily in the encounter step (Delta G1) of H26 with mutant HEL(R21Q). Overall, in the process of complex formation with lysozyme, the mutations HEL(R21X) affect primarily the docking phase of H10 association and both phases of H26. Our results are consistent with the interpretation that the free energy barriers to conformational rearrangement are highest in H26, especially with mutant antigen.

Anti-neutrophil cytoplasmic antibodies (ANCA) from patients with systemic vasculitis recognize restricted epitopes of proteinase 3 involving the catalytic site

ANCA with specificity for proteinase 3 (PR3), a neutrophil primary granule enzyme, are of diagnostic value in Wegener's granulomatosis (WG) and certain other forms of systemic vasculitis. There is evidence to suggest that they play a pathogenic role in disease, and that the interaction of ANCA with PR3 is likely to be important. We showed, using a resonant mirror biosensor, that C-ANCA from different patients recognized the same or closely related epitopes on PR3. Studies using linear peptides in the SPOT system confirmed the highly restricted nature of this interaction and identified five linear epitopes. Fluid-phase inhibition studies, using a different set of peptides, validated the sequences involved. Using a computer-generated model of the structure of PR3, four of five epitopes were shown to be intimately linked with the catalytic site. The restricted number of epitopes, and their location at the catalytic site, has important implications for the role of C-ANCA in the pathogenesis of vasculitis.

Small molecule-based chemical affinity system for the purification of proteins

A new chemical affinity system is described for the purification of proteins. The Linx Affinity Purification System enables researchers to quickly and easily bind a protein ligand to a chromatographic matrix and use the resulting affinity resin to purify a second protein from crude mixtures. The entire process takes approximately 2 h.

Bioaffinity based immobilization of enzymes

Procedures that utilize the affinities of biomolecules and ligands for the immobilization of enzymes are gaining increasing acceptance in the construction of sensitive enzyme-based analytical devices as well as for other applications. The strong affinity of polyclonal/monoclonal antibodies for specific enzymes and those of lectins for glycoenzymes bearing appropriate oligosaccharides have been generally employed for the purpose. Potential of affinity pairs like cellulose-cellulose binding domain bearing enzymes and immobilized metal ionsurface histidine bearing enzymes has also been recognised. The bioaffinity based immobilization procedures usually yield preparations exhibiting high catalytic activity and improved stability against denaturation. Bioaffinity based immobilizations are usually reversible facilitating the reuse of support matrix, orient the enzymes favourably and offer the possibility of enzyme immobilization directly from partially pure enzyme preparations or even cell lysates. Enzyme lacking innate ability to bind to various affinity supports can be made to bind to them by chemically or genetically linking the enzymes with appropriate polypeptides/domains like the cellulose binding domain, protein A, histidine-rich peptides, single chain antibodies, etc.

Production of glutathione-coated microtitre plates for capturing recombinant glutathione S-transferase fusion proteins as antigens in immunoassays

Glutathione S-transferase (GST) is commonly used as a fusion partner in producing recombinant proteins and this technology is increasingly being used to produce antigens for use in immunoassays to measure antibodies. To circumvent the requirement to purify such antigens before use, we developed a method for coupling glutathione to microtitre plates so that GST-containing recombinant proteins could be purified and immobilised in one step in a suitable state for immunoassays. This procedure involves covalent linkage (using the heterobifunctional cross-linker sulphosuccinimidyl 4-(p-maleimidophenyl)butyrate) of reduced glutathione through its sulphydryl group to lysine residues of haemoglobin previously immobilised on microtitre plates. Haemoglobin was superior over other proteins tested in giving the lowest non-specific binding; in this regard it was also important to limit the amount of cross-linker used to 0.1 mM. Using glutamic acid decarboxylase as a model antigen, the new affinity capture assay was at least as good as the two-step procedure involving direct adsorption to plates of previously purified antigen; it may have the additional advantage of preserving the antigen in a more native conformation than direct adsorption. The new assay also performed as well as an assay using anti-GST antibodies adsorbed onto plates; glutathione plates, unlike anti-GST plates, will only capture recombinant proteins containing functional GST--a significant point for some recombinant expression systems in which a large proportion of the protein product is insoluble because of incorrect folding.

Automated microanalysis using magnetic beads with commercial capillary electrophoretic instrumentation

The potential of a new microanalytical method using magnetic beads (MBs) and commercial capillary electrophoresis (CE) instrumentation for performing enzymatic and inhibition assays, as well as for analysis of biological molecules such as antigens, substrates, etc., has been explored. A small quantity of magnetic beads containing immobilized biomolecules was injected into a neutral hydrophilic-coated fused-silica capillary. The short plug (2-3 mm) of beads was held fixed by a magnet placed in the cartridge of the CE system, without the use of frits. The beads could be replaced after each run, eliminating the need to regenerate the solid support. Two protocols were used for analysis: sequential injection (SI) and SI followed by isotachophoretic (ITP) focusing. Alkaline phosphatase (AP) and HIV-protease were used to demonstrate the SI procedure for enzymatic and inhibition assays. The second protocol, SI/ITP, was employed to quantitate an antigen (mouse mAB) using antibodies (sheep IgG towards mouse AB) immobilized on the beads. The MB-CE method, requiring only femtomole (fmol) quantities of material, can potentially be employed in diagnostic and forensic assays, kinetic studies and searching for inhibitors, ligands, receptors, etc.

Chemical modification of earthworm fibrinolytic enzyme with human serum albumin fragment and characterization of the protease as a therapeutic enzyme

The strongest fibrinolytic protease (F-III-2) in the six enzyme proteins purified from earthworm, Lumbricus rubellus [N. Nakajima et al., Biosci. Biotech. Biochem., 57, 1726-1730 (1993)] has been modified chemically with fragmented human serum albumin (mol. wt., 10,000-30,000). The modified enzyme lost the antigenicity of the native enzyme and reacted with the antisera against human serum albumin, the human serum albumin fragments, and the conjugate with the native enzyme to form precipitation lines, which fused with each other. The conjugate was significantly more resistant to inactivation by protease inhibitors in rat plasma. The enzyme was a non-hemorrhagic protein and did not induce platelet aggregation. The enzyme kept potent proteolytic activity for fibrin and fibrinogen than that of human plasmin. The enzyme easily solubilized actual fibrin clots (thrombi) of whole blood induced by thrombin in a rat's vena cava. The continuous fibrinolysis for fibrin suspension in an enzyme reactor system using the modified enzyme immobilized to oxirane-activated acrylic beads has been achieved without any inactivation of the activity at least for more than 1 month. The N-terminal amino acid sequence of the protein was also investigated and the sequence showed local similarity to those of the serine proteases such as plasmin and chymotrypsin.

[Noncovalent immobilization of catalase on antibodies adsorbed on carbon fabric]

Catalase was immobilized on an immunosorbent prepared by anticatalase adsorption on an activated carbon fabric (ACF), and its kinetic parameters were determined. The immobilized catalase activity depended on the binding capacity of anticatalase. Under the optimum conditions (6 micrograms/mg anticatalase, 5.24 nM catalase) the immobilized catalase activity was 1.5-ford higher as compared to soluble catalase. Antibodies stabilized soluble catalase, but decreased its thermostability on immobilization of immunocomplexes on ACF. Noncovalent immobilization of catalase on adsorbed antibodies opens up the way to the use of this approach for immobilization of other oligomeric enzymes.

[Immunochemical study of modified forms of L-asparaginase]

Certain catalytic and immunological properties of L-asparaginase modified by polyglucin were studied. It was shown that the modified forms of L-asparaginase maintained high catalytic activity (Km 0.80.10(-5)-1.89.10(-5) M) and at the same time appeared to be more resistant to inactivation under the effect of antibodies.

Immunochemical detection by specific antibody to thrombin of prothrombin conformational changes upon adsorption to artificial surfaces

Polyclonal antihuman alpha-thrombin antibodies produced in rabbits reacted minimally (less than 0.05%) in solution with human prothrombin. However, when prothrombin was adsorbed to artificial surfaces such as polyvinyl chloride (PVC), the cross-reactivity of surface-bound prothrombin with antibody IgG to thrombin (greater than 95% purity) was shown to be significantly enhanced. On PVC, the molar ratios of antibody IgG to thrombin/prothrombin approached the same level as that of antibody IgG to thrombin/thrombin when thrombin was adsorbed to the same material. The analyses of antigen-antibodies interaction, in solution with a direct binding assay by immune precipitation at high-speed centrifugation (160,000 g, 30 min), and on solid-phase PVC, were accomplished by use of double-labeling technique, i.e., 131I-thrombin (or 131I-prothrombin) and 125I-antibody IgG to thrombin. The results appear to suggest that prothrombin adsorption to PVC has resulted in some molecular conformational changes so that immunologically the adsorbed prothrombin resembles that of adsorbed thrombin on the same PVC surface.

Acrylic microspheres in vivo V: Immunological properties of immobilized asparaginase in microparticles

L-Asparaginase was immobilized in microparticles of polyacrylamide. Such particles were then injected by intramuscular/subcutaneous, intraperitoneal, or intravenous routes into mice to investigate the immunological consequences of the immobilization. Entrapment of L-asparaginase in microparticles did not prevent the formation of antibodies in intensively treated animals. Intraperitoneal and intravenous injections of particles produced significantly higher antibody levels than soluble L-asparaginase. Antigen administered intramuscularly/subcutaneously in microparticles elicited, however, a weak immune response. Dependent on the route of administration, the particles may thus function as an adjuvant. A modified Arthus reaction in the foot pads of immunized mice indicated that antigenicity decreased when L-asparaginase was immobilized in microparticles. Injection of free L-asparaginase, intramuscularly/subcutaneously (2 x 20 IU) in the preimmunized mice produced no effects on the serum level of L-asparagine, whereas intramuscular/subcutaneous injection of L-asparaginase in microparticles produced a depression of the serum concentration. It is concluded that the intramuscular/subcutaneous injection of L-asparaginase in microparticles is the choice route of administration with respect to duration and the immunological reaction.

Stimulation of cytolytic T cells by isolated viral peptides and HN protein coupled to agarose beads

Sendai virus-infected mouse cells can be lysed by mouse cytolytic thymus-dependent lymphocytes (CTL) directed specifically against the infected cells. The CTL is known to recognise the H-2 antigens on the target cells together with structure(s) including at least the two viral surface glycoproteins also found on purified virus. We report here that anti-Sendai CTL can be stimulated in vitro by detergent-solubilised viral haemagglutinin-neuraminidase (HN), either as the isolated protein or coupled to agarose beads. We further show stimulation by the hydrophilic portion of a protein removed from the virus by the protease subtilisin BPN', and we demonstrate that cyanogen bromide- (CNBr-) cleaved viral peptides also produce such stimulation.

Immunological evaluation of repeated administration of erythrocyte-entrapped protein to C3H/HeJ mice

The immunogenicity of heterologous protein entrapped in autologous erythrocytes was evaluated in a mouse system. Multiple intravenous administrations of an erythrocyte-entrapped bovine beta-glucuronidase preparation resulted in little, if any, immunological response to the entrapped protein or erythrocyte carrier. Erythrocyte entrapment also protected protein from circulating antibody elicited by prior subcutaneous sensitization with unentrapped enzyme in adjuvant. Thus erythrocyte entrapment may protect potentially immunogenic agents from immunological surveillance.