Immunoaffinity chromatography utilizing monoclonal antibodies. Factors which influence antigen-binding capacity

A novel antihuman C3d monoclonal antibody with specificity to the C3d complement split product

The complement component C3 and the cleavage products of C3b/iC3b, C3c and C3d are used as biomarkers in clinical diagnostics. Currently, no specific antibodies are able to differentiate C3d from other fragments, although such a distinction could be very valuable considering that they may reflect different pathophysiological mechanisms. We have developed a rat antihuman C3d monoclonal antibody with specificity to the end sequence of the N-terminal region of C3d. The antibody can therefore only bind to C3d when it manifests itself as the final end product of cleaved C3. We believe that this specificity is it first of its kind, and predicts that it can be used as a detection tool in several immunological methods with great value in diagnostics.

A specific assay for quantification of human C4c by use of an anti-C4c monoclonal antibody

The increasing evidence of the implication of the complement system in the pathogenesis of several diseases has emphasized the need for the development of specific and valid assays, optimized for quantitative detection of complement activation in vivo. In the present study, we have developed a mouse monoclonal antibody (mAb) that is able to detect fluid phase C4c without interference from other products generated from the complement component C4. The C4c specific mAb was tested in different enzyme-linked immunosorbent assay (ELISA) combinations with various types of in vitro activated sera and samples from factor I deficient patients. The specificity of the mAb was further evaluated by immunoprecipitation techniques and by analysis of eluted fragments of C4 after immunoaffinity chromatography. The anti-C4c mAb was confirmed to be C4c specific, as it showed no cross-reactivity with native (un-cleaved) C4, C4b, iC4b, or C4d. Also, no reaction was observed with C4 fragments in factor I deficient plasma or serum samples. We established and validated a sandwich ELISA based on this C4c specific antibody. The normal range of C4c in EDTA/futhan plasma collected from 100 Danish blood donors was measured, with a mean of 0.85mg/L and a range of 0.19-2.21mg/L. We believe that the C4c specific antibody and the ELISA might be important tools in the future assessment of in vivo activation in situations where the classical or the lectin complement pathways are involved in the pathogenesis.

Interleukin-11 drives early lung inflammation during Mycobacterium tuberculosis infection in genetically susceptible mice

IL-11 is multifunctional cytokine whose physiological role in the lungs during pulmonary tuberculosis (TB) is poorly understood. Here, using in vivo administration of specific antibodies against IL-11, we demonstrate for the first time that blocking IL-11 diminishes histopathology and neutrophilic infiltration of the lung tissue in TB-infected genetically susceptible mice. Antibody treatment decreased the pulmonary levels of IL-11 and other key inflammatory cytokines not belonging to the Th1 axis, and down-regulated IL-11 mRNA expression. This suggests the existence of a positive feedback loop at the transcriptional level, which is further supported by up-regulation of IL-11 mRNA expression in the presence of rIL-11 in in vitro cultures of lung cells. These findings imply a pathogenic role for IL-11 during the early phase of Mycobacterium tuberculosis-triggered disease in a genetically susceptible host.

Serum concentration and interaction properties of MBL/ficolin associated protein-1

Recently, a novel protein named MBL/ficolin associated protein-1 (MAP-1) derived from the MASP1 gene through differential splicing was identified. In the present study, we established biochemical characteristics, determined the serum level and assessed the interactions between the lectin complement pathway (LCP) recognition molecules and MAP-1. We expressed recombinant MAP-1 in CHO DG44 cells, developed a quantitative ELISA assay based on a MAP-1 specific monoclonal capture antibody and measured the serum levels in 100 Danish blood donors. In addition we assessed the association properties between MAP-1 and Ficolin-2, -3 and MBL in serum using ELISA and density gradient ultra centrifugation. When recombinant MAP-1 was subjected to N-glycosidase F treatment the molecular mass decreased from ∼45 kDa to ∼40 kDa equivalent with the calculated molecular mass from the deduced amino acid sequence without the signal peptide. We found that serum MAP-1 was very stable when subjected to repeated freeze and thaw cycles. The mean serum concentration of MAP-1 was found to be 240 ng/ml (range: 115-466 ng/ml). MAP-1 was predominantly found in complex with Ficolin-3 and to a lesser degree with Ficolin-2 and MBL and by use of density gradient ultra centrifugation we could show that the major part of serum MAP-1 circulates in complex with the LCP molecules. In conclusion, these results show that MAP-1 is a highly stable glycosylated human serum protein found in complex with Ficolin-3, Ficolin-2 and MBL.

The atherogenic bacterium Porphyromonas gingivalis evades circulating phagocytes by adhering to erythrocytes

A relationship between periodontitis and coronary heart disease has been investigated intensively. A pathogenic role for the oral bacterium Porphyromonas gingivalis has been suggested for both diseases. We examined whether complement activation by P. gingivalis strain ATCC 33277 allows the bacterium to adhere to human red blood cells (RBCs) and thereby evade attack by circulating phagocytes. On incubation with normal human serum, the P. gingivalis strain efficiently fixed complement component 3 (C3). Incubation of bacteria with washed whole blood cells suspended in autologous serum resulted in a dose- and time-dependent adherence to RBCs. The adherence required functionally intact complement receptor 1 (CR1; also called CD35) on the RBCs and significantly inhibited the uptake of P. gingivalis by neutrophils and B cells within 1 min of incubation (by 64% and 51%, respectively) and that by monocytes after between 15 min and 30 min of incubation (by 66% and 53%, respectively). The attachment of C3b/iC3b to bacterium-bearing RBCs decreased progressively after 15 min, indicating that conversion of C3 fragments into C3dg occurred, decreasing the affinity for CR1 on RBCs. We propose that P. gingivalis exploits RBCs as a transport vehicle, rendering it inaccessible to attack by phagocytes, and by doing so plays a role in the development of systemic diseases.

Generation of a C3c specific monoclonal antibody and assessment of C3c as a putative inflammatory marker derived from complement factor C3

There is a general need for markers of systemic inflammation in acute or chronic diseases, where complement activation is involved. Available methods to monitor complement activation are elaborate and of low sensitivity; they include haemolytic assays (CH50), quantification of fluid phase terminal complex (C5b-C9) and quantification of complement split products by precipitation-in-gel techniques (e.g. C3d). We have developed a mouse monoclonal antibody (mAb) that is able to detect fluid phase C3c without interference from other products generated from the complement component C3. The C3c specific mAb was tested in different ELISA combinations with various types of in vitro activated sera and with plasma or serum samples from factor I deficient patients. The specificity of the mAb was evaluated in immunoprecipitation techniques and by analysis of eluted fragments of C3 after immunoaffinity chromatography. The C3c mAb was confirmed to be C3c specific, as it showed no cross-reactivity with native (un-cleaved) C3, with C3b, iC3b, or with C3d. Also, no significant reaction was observed with C3 fragments in factor I deficient sera or plasma. This antibody forms the basis for the generation of a robust ELISA that allows for a quick and reliable evaluation of complement activation and consumption as a marker for inflammatory processes. We established the C3c plasma range in 100 healthy Danish blood donors with a mean of 3.47 μg/ml and a range of 2.12-4.92 μg/ml. We believe that such an antibody might be of potential value in the assessment of in vivo complement activity during the inflammatory processes.

MBL-associated serine protease-3 circulates in high serum concentrations predominantly in complex with Ficolin-3 and regulates Ficolin-3 mediated complement activation

BACKGROUND

The human lectin complement pathway (LCP) involves circulating complexes consisting of mannose-binding lectin (MBL) or ficolins in association with serine proteases named MASP-1, -2 and -3 and a non-enzymatic protein, sMAP. MASP-3 originates from the MASP1 gene through differential splicing and little is known about its biological characteristics. For this reason we expressed recombinant MASP-3 and generated specific monoclonal antibodies to establish biochemical characteristics and to determine the serum levels, the interactions with the LCP recognition molecules and the influence on complement activation of MASP-3.

METHODS

We expressed rMASP-3 in CHO-DG44 cells and used SDS-PAGE and Western blotting for biochemical characterization. We generated monoclonal antibodies against MASP-3 and developed a quantitative MASP-3 assay to establish the serum levels in 100 Danish blood donors. In addition we assessed the association levels between MASP-3 and Ficolin-2, -3 and MBL using both ELISA and immunoprecipitation techniques. Moreover, we assessed the influence on complement factor C4 deposition.

RESULTS

We found the mean serum MASP-3 concentration to be 6.4mg/l (range: 2-12.9mg/l) and that MASP-3 in serum is primarily found in complex with Ficolin-3. In contrast to this the MASP-3 association with Ficolin-2 and especially with MBL seems to be less evident. rMASP-3 significantly inhibited Ficolin-3 mediated C4 deposition, while the opposite was the case for rMASP-1.

CONCLUSION

Our results show that MASP-3 is present in relatively high serum concentrations. Moreover, Ficolin-3 is the primary acceptor molecule of MASP-3 among the LCP activator molecules, but MASP-3 appears to down-regulate Ficolin-3 mediated complement activation through the lectin pathway.

Coimmunoprecipitation and proteomic analyses

Defining protein-protein interaction networks is a major goal of proteomics. Here, we present a protocol for coimmunoprecipitation, a technique suitable for the isolation of whole protein complexes in vivo and their subsequent identification by either immunoblotting or mass spectrometric sequencing combined to database search.

Integrating molecular detection and response to create self-signalling antibodies

Monoclonal antibodies are reproducible, specific, and cost-effective molecular probes; use outside the laboratory is, however, restricted by technical limitations. Addressing these constraints, the first self-signalling antibodies are now described, where specific antigen binding causes release of bound reporter from bispecific antibodies (BsAb) to generate a detectable signal. The report examines the concept that two different antibody binding sites in close proximity can promote interaction between molecules recognised by these sites, generating a signal by molecular crowding. Signal strength is found to increase with increasing homogeneity for a BsAb reactive with multimeric surfactant antigen; signal response is linear for a BsAb reactive with univalent small analyte deoxypyridinoline. Self-signalling is consistent with intramolecular steric hindrance. This is the first report detailing integration of two different functions, molecular detection and signal response, into BsAbs and with detection of large and small analytes, has generic application to antibody-based systems.

Comparison of different ligand densities for the manufacture of CB Hep-1 immunosorbents

Different ligand densities of monoclonal antibody (Mab) CB.Hep-1 were studied during covalent coupling on Sepharose CL-4B for recombinant hepatitis B surface antigen (rHBsAg) immunoaffinity purification. Ligand densities of 2.2, 3.2, 4.2 and 5.2 mg Mab/ml immunosorbents, respectively, were assayed during five cycles of immunoaffinity chromatography (IAC). Adsorption capacities averaged either 3.2 mg/ml (0.57 mg rHBsAg/ml immunosorbent/5.42 mg of total purified protein) or 5.2 mg/ml (0.56 mg rHBsAg/ml immunosorbent/5.05 mg total purified protein). Immunosorbents showed ligand leakage levels below 3 ng Mab/microg rHBsAg. Antigen purity was higher than 95% in all cases. The results suggest that a ligand density (LD) of 3.2 mg Mab/ml immunosorbent should be used for immunoaffinity chromatography because no significant differences were found in the ligand densities studied (P-value=0.012), which saves 40% of CB.Hep-1 immunosorbent manufacturing cost in comparison with 5 mg Mab/ml immunosorbent, which is currently used in large-scale production.

The solid phase in affinity chromatography: strategies for antibody attachment

Antibodies (Ab) are commonly used in affinity chromatography (AC) as a versatile and specific means of isolating target molecules from complex mixtures. A number of procedures have been developed to immobilize antibodies on the solid matrix. Some of these methods couple the antibody via chemical groups that may be important for specific recognition of antigen, resulting in loss of functionality in a proportion of the antibodies. In other methods, the outcome of immobilization is coupling via unique sites in the Fc region of the antibody molecule, ensuring orientation of the antibody combining sites (Fab) towards the mobile phase. This review discusses the advantages and disadvantages of the various methods available for immobilization and outlines protocols for site-directed, covalent coupling of the antibody to the solid phase that essentially retains the activity of the antibody.

Online single-step analysis of blood proteins: the transferrin story

The serum iron transport protein human transferrin (hTf) is a glycoprotein (MW approximately 79.6 kDa) containing two Asn-linked sites of glycosylation. The presence of specific glycoforms of hTf has been used as an indicator of carbohydrate-deficient glycoprotein syndrome (CDGS) or an indicator of alcohol abuse. The exact nature of the glycoforms described in the literature is controversial. In this work we demonstrate that the altered hTf glycoforms have lost one or both complete glycan side chains. Furthermore, we demonstrate using a combination of online immunoaffinity-postconcentration-mass spectrometry in conjunction with a blood spot cartridge that we can determine the relative quantities of the hTf glycoforms using <5 microL blood in under 30 min. This is in contrast to previous methods that used 1 mL and took 4 days. We show that this method can be useful to analyze hTf from CDGS and alcoholic patients.

Stirrer tank: an appropriate technology to immobilize the CB.Hep-1 monoclonal antibody for immunoaffinity purification

The CB.Hep-1 monoclonal antibody was coupled to CNBr-activated Sepharose CL 4B at three different immobilization scales for purification of recombinant hepatitis B surface antigen. Standard laboratory apparatus to obtain immunosorbents of 1 l (scale I) and 3 l (scale II) as well as a stirrer tank to prepare 6 l immunosorbents (scale III) were used. The binding capacity at scale III was 2- and 1.5-fold higher with respect to the scales II and I, while a reduction in the ligand leakage of 5- and 2-folds was observed. Immunosorbents from scale II showed a significantly reduced adsorption, and an increased ligand leakage. Differences in the coupling efficiency were not observed. Antigen purity eluted from the immunosorbents was always above 85%.

Rapid Determination of Transferrin Isoforms by Immunoaffinity Liquid Chromatography and Electrospray Mass Spectrometry

Background: Congenital disorders of glycosylation (CDG) are autosomal recessive disorders that produce increased serum carbohydrate-deficient transferrin (CDT) isoforms. Methods to resolve CDT from fully glycosylated transferrin (Trf) have been based on a neutral shift in the isoelectric focusing (IEF) pattern or on a reduction in the negative charge, allowing resolution by anion-exchange chromatography. Our purpose was to develop a method of resolution and relative quantification of Trf isoforms using online immunoaffinity liquid chromatography–mass spectrometry (LC-MS).

Methods: Serum (25 μL) was diluted with 100 μL of water before application to an immunoaffinity column that sequestered Trf isoforms. Trf isoforms were eluted from the immunoaffinity column, concentrated on a C4 column, eluted from the C4 column, and introduced into the mass spectrometer. Analysis of the Trf isoforms was entirely automated and completed in &lt;10 min per sample.

Results: The LC-MS method demonstrated that the major abnormal Trf isoforms in CDG lack one complete oligosaccharide structure (mono-oligosaccharide) or both oligosaccharide structures (a-oligosaccharide), but not the sialic acids, as presumed on the basis of IEF methods. Calculation of relative ratios among three possible species (mono-/di-oligosaccharide and a-/di-oligosaccharide) is reproducible [mean intra- and interassay CVs were 9.3% (n = 10) and 10% (n = 5), respectively]. A reference range for patients &lt;18 years was determined by analysis of 209 samples (for mono-/di-oligosaccharide, the median was 0.041 and the range was 0.018–0.083; for a-/di-oligosaccharide, the median was 0.007 and the range was 0.002–0.036). Comparison of data obtained with an affinity chromatography-IEF method and the LC-MS method demonstrated equivalence in the interpreted results (n = 170).

Conclusions: Advantages of the LC-MS method include improved sensitivity, minimal sample preparation, and an analysis time of &lt;10 min. The method was automated, which allowed high throughput, with &gt;100 samples analyzed in a single day. Moreover, the nature of the oligosaccharide defect in CDG is accurately reflected by mass resolution, and subtle oligosaccharide truncations may also be detected by this method.

Affinity purification of polyclonal antibodies using immobilized multimeric peptides

The possibility of using multiple antigenic peptides (MAP) not only for the production and characterisation of antibodies but also for their purification by affinity chromatography, has been explored with two different tetrameric MAPs synthesised starting from a tetradentate lysine core. Recognition selectivity and specificity of the multimeric antigens were retained after immobilization on preactivated affinity supports, allowing convenient antibody purification directly from crude sera in a single chromatographic step. Since antibodies raised against MAPs recognise very frequently the N-terminal portion of the peptide antigen, results suggest that only a limited number of peptide chains remains covalently linked to the solid phase, leaving the others uncoupled and free to interact fully with the antibody. Recovery of antibody immunoreactivity from affinity purifications on MAP-columns was much higher than that obtained from columns prepared by immobilizing at the same density the corresponding linear peptide antigen. The purity of thus obtained antibodies is also far superior, as detected by SDS-PAGE analysis. Retention of the multimeric peptide recognition properties for the corresponding antibodies after immobilization on solid supports suggests that production, characterization, and even the affinity purification of anti-peptide antibodies, could be carried out simply and conveniently via the synthesis of a single multimeric antigen, without additional steps.

Comparison of methods for immobilization to carboxymethyl dextran sensor surfaces by analysis of the specific activity of monoclonal antibodies

The authors have recently described the development of a carboxymethyl dextran-based sensor surface for biospecific interaction analysis by surface plasmon resonance. Ligands are immobilized via primary amine groups after activation of the carboxymethyl groups on the sensor surface with a mixture of N-hydroxysuccinimide and N-ethyl-N'-(dimethylaminopropyl) carbodiimide. Methods have now been developed for efficient immobilization via thiol/disulfide exchange, aldehyde coupling and biotin-avidin coupling. The specific activity of monoclonal antibodies immobilized by the four different methods was investigated by altering the immobilization conditions, e.g., activation time, protein concentration, ionic strength and the degree of modification, etc. Investigations have also been made concerning possible differences in the specific activity for antibodies immobilized using optimized conditions with respect to the four different chemistries. These studies show that, with the flexible carboxymethyl dextran matrix used here, the immobilization methods give rise to only minor differences in specific activity. Thus, with this solid support, a 'site directed' immobilization strategy for monoclonal antibodies has no advantage. In general the specific activity for optimized systems was approximately 75% for the binding of beta 2 mu-globulin to an immobilized monoclonal antibody directed against beta 2 mu-globulin. Reduced specific activities of immobilized antibodies induced by variation of the coupling conditions could be attributed to the deterioration of the active site of the antibody.

Streptococcal erythrogenic toxin type C is not a phosphorylated protein. Description of two different purification procedures and investigation of its phosphorylation state

Erythrogenic toxin type C (ETC) from different streptococcal group A strains was successively purified by absorption on phenylsepharose, acidic dialysis of the eluate at 40% saturated ammonium sulphate solution, CM-Sepharose chromatography, finally by immunoaffinity chromatography on monoclonal antibodies. Second, after growing of bacteria in the presence of [32P]orthophosphate to phosphorylate ETC, the ETC was purified with phenylsepharose following immunoaffinity chromatography. The occurrence of phosphoamino acids in the purified ETC was investigated by an immunoassay. No phosphoamino acids could be detected in the ETC molecule. Also after radiolabelling with 32P it was not possible to demonstrate a radioactive signal. The treatment with alkaline phosphatase has no influence on the mitogenicity or position of ETC in isoelectric focusing. The results obtained led to the conclusion that in contrast to the literature, ETC is not a phosphorylated protein.

Coupling of antibody-binding fragments to solid-phase supports: site-directed binding of F(ab')2 fragments

A method to covalently bind antibody fragments, via their carboxyl termini to solid supports, is presented. The strategy involves: (1) reversibly blocking all the accessible carboxyl groups on the antibody molecule with phenylhydrazine, (2) exposing the carboxyl termini of the fragment by enzymatic digestion with pepsin and (3) subsequently coupling the fragment to an appropriate support. Experiments with an anti-bovine serum albumin monoclonal antibody and C-14 phenylhydrazine revealed that the blocking step was nearly completely reversible with a dilute solution of FeCl3. Radioiodinated blocked F(ab')2 fragments were then coupled to an amino-functionalized Sepharose 4B column, and characterized as to their coupling capacity (mass of protein coupled/ml of bead), and antigen-binding activity. The coupling capacity of the blocked fragments was found to be 12%, half the coupling efficiency of unmodified radioiodinated F(ab')2. The antigen-binding capacity (mol antigen bound per mol antibody coupled) for the blocked F(ab')2, on the other hand, was found to be 1.9, which was approx. 3.5-times greater than for the unmodified F(ab')2. Comparisons with other conventional coupling techniques were also made. These preliminary studies suggest that this technique can provide one with the means to obtain more uniform and active populations of immobilized antibody fragments.

The topology of the glutamine and ATP binding sites of human asparagine synthetase

Human asparagine synthetase was examined using a combination of chemical modifiers and specific monoclonal antibodies. The studies were designed to determine the topological relation between the nucleotide binding site and the glutamine binding site of the human asparagine synthetase. The purified recombinant enzyme was chemically modified at the glutamine binding site by 6-diazo-5-oxo-L-norleucine (DON), and at the ATP binding site by 8-azidoadenosine 5'-triphosphate (8-N3ATP). The effects of chemical modification with DON included a loss of glutamine-dependent reactions, but no effect on ATP binding as measured during ammonia-dependent asparagine synthesis. Similarly, modification with 8-N3ATP resulted in a loss of ammonia-dependent asparagine synthesis, but no effect on the glutaminase activity. A series of monoclonal antibodies was also examined in relation to their epitopes and the sites modified by the two covalent chemical modifiers. It was found that several antibodies were prevented from binding by specific chemical modification, and that the antibodies could be classified into groups correlating to their relative binding domains. These results are discussed in terms of relative positions of the glutamine and ATP binding sites on asparagine synthetase.

Group V allergens in grass pollens: IV. Similarities in amino acid compositions and NH2-terminal sequences of the group V allergens from Lolium perenne, Poa pratensis and Dactylis glomerata

Monoclonal antibodies (PpV4) raised against Phleum pratense group V allergen were used for immuno-affinity chromatography of cross-reacting group V allergens from related grass species. Fractions enriched in group V allergen were obtained from Lolium perenne, Poa pratense and Dactylis glomerata extracts. The major components in these fractions were found in the Mwr range 25-28 kD. IgE binding to these components was shown using a pool of grass allergic sera, by SDS-PAGE immunoblotting. These fractions were electroblotted from tricine SDS-PAGE gels onto a polyvinylidene-difluoride membrane and selected group V bands were directly cut out and used for amino acid analysis and NH2-terminal sequencing. Both the amino acid compositions and the NH2-terminal sequences obtained for each group V allergen were almost similar to each other and to the sequence and composition of the previously described allergen Phl p V from Phleum pratense. A common trait of the investigated allergens, is the very high contents of alanine (25-32%) and the presence of the modified amino acid, hydroxyproline.

Immunoaffinity purification: Basic principles and operational considerations

Immunoaffinity purification has become an important technique in biotechnology. In this review the basic principles of immunoaffinity separations are described with respect to the stages of operation and potential application. The most commonly used support materials, activation procedures, and coupling chemistries are compared to one another for suitability in various applications. Individual operational steps for fixed bed immunoadsorbents including loading, washing, elution and regeneration are described in terms of both theory and practice. Factors influencing adsorbent stability are identified, and alternative operation and configuration strategies are discussed in light of their application to immunoaffinity systems.

Immunoassay in the presence of water-soluble polymers

To overcome the adverse consequences of antibody immobilization (impairment of the antigen-binding parameters) the interaction of a number of antigens with both soluble and covalently immobilized antibodies in the presence of water-soluble polymers has been investigated. Incorporation of some water-soluble polymers (Ficoll, Dextran) into the assay mixture was shown to substantially increase the antigen-binding capacity of both soluble and immobilized antibodies. The use of dextran T70 enhanced the sensitivity of competitive radioimmunoassays for CEA and beta 2-microglobulin 3-4-fold. This procedure may be also applied to shorten the incubation period when performing an assay.

Factors affecting the specific activity of immobilized antibodies and their biologically active fragments

Factors affecting the specific activity of immobilized antibodies and their biologically active fragments were studied with goat anti-mouse and goat anti-human immunoglobulin G. Antibodies were immobilized on HW 65 polymeric support matrix activated with carbonyldiimidazole, hydrazide and iodoacetic acid. The most significant factors influencing the specific activity of stochastic coupling of antibodies are multi-site attachment, multiple orientations and steric hindrance imposed by crowding of antibody and the size of the antigen. In oriented immobilization the specific activity is affected only by steric hindrance. The specific activity of immunosorbents prepared by immobilization of F(ab') fragments can be improved to almost 100% by limiting the amount of protein immobilization and the size of the antigen. The present study shows the protocols for optimizing immobilized antibody performance.

Selection of monoclonal antibodies for immunoaffinity chromatography: model studies with antibodies against soy bean trypsin inhibitor

To facilitate selection of monoclonal antibodies for immunoaffinity chromatography, an ELISA screening procedure was developed. The assay is based on the avidin-biotin system and provides a profile of the monoclonal antibody which is based on the binding characteristics of the antigen binding site when exposed to different elution reagents. The elution profiles of 5 monoclonal antibodies to soy bean trypsin inhibitor (SBTI) were determined and for 2 of the antibodies the results obtained in the ELISA were verified using column experiments. The affinity constants were determined for the same 5 monoclonal antibodies and no correlation was seen with the ease of elution. The elution profiles presented here are easily obtained and the results indicate that a general screening procedure for suitable combinations of antibodies and elution conditions can be carried out using an elution ELISA assay when modified as described herein.

Synthetic peptides of envelope proteins of two different strains of simian AIDS retrovirus (SRV-1 and SRV-2) represent unique antigenic determinants for serum neutralizing antibodies

There are at least three distinct serotypes of simian type D retrovirus (SRV) which exhibit extensive serological cross-reactivity, but no cross-reactivity exists at the level of serum neutralizing antibodies. Amino acid sequence analysis and hydrophobicity plots of SRV-1 and SRV-2 envelope proteins were compared in order to identify unique potential antigenic determinants to which respective neutralizing antibodies may be directed. Peptides representing residues 147-162 of SRV-1 and 96-102 of SRV-2 were synthesized and assessed for their immunoreactivity. Free peptide inhibition of strain-specific serum (rhesus) neutralizing antibodies to SRV-1 and SRV-2 was demonstrated using the SRV-1 147-162 peptide and the SRV-2 peptide, 96-102, respectively. Inhibition of serum neutralizing activity by these peptides was also strain-specific, showing no cross-inhibition. SRV-1 147-162 conjugated to a protein carrier and cross-linked to Sepharose beads specifically adsorbed neutralizing antibodies from SRV-1 immune rhesus sera. The antibodies eluted from the immunoadsorbent possessed SRV-1 neutralizing activity, but showed no effect on the infectivity of SRV-2. Peptide SRV-1 147-162 also exhibited the capacity to bind specifically with a mouse monoclonal antibody which neutralizes the infectivity of SRV-1. Mice immunized with a recombinant SRV-1 envelope protein or with whole, inactivated SRV-1 produced antibodies which bound the SRV-1 147-162 conjugate, but not the protein carrier itself. Mouse antibodies to the SRV-1 147-162 conjugate exhibited specific binding with both native SRV-1 and with recombinant SRV-1 envelope protein. These findings provide strong evidence that SRV-1 147-162 and SRV-2 96-102 constitute at least two unique antigenic determinants, or parts thereof, which participate in the strain-specific neutralizing antibody response. Moreover, the findings indicate that the SRV-1 neutralizing antibodies produced by monkeys and at least a certain population of neutralizing antibodies produced by mice recognize the same epitope of SRV-1.

Tresyl-activated support for high-performance affinity chromatography

A new activated support TSK gel Tresyl-5PW was evaluated for the coupling of antibodies, which was found to occur easily under mild conditions with high yields. Optimum coupling conditions were a 2-h reaction at 25 degrees C in 1 M phosphate buffer (pH 7.5) when 2-3 mg antibody/ml support is to be coupled and a 6-7-h reaction when ca. 10 mg antibody/ml support is to be coupled. When antibodies were coupled under these conditions, antibody coupling yields greater than 80% and antigen binding efficiencies of 70-80% were achieved, probably owing to a selective attachment of the Fc region of the antibodies. Antigens (human serum proteins) could be separated rapidly without denaturation on antibody-coupled Tresyl-5PW.

Production and use of rat monoclonal antibodies to the human myeloid cell nuclear differentiation antigen

A dot immunoblot screening assay was used to identify rat monoclonal antibodies to a human myeloid cell differentiation-specific nuclear antigen (MNDA). The selection was based on the positive reaction of hybridoma cell supernatants with a concentrated nuclear protein extract prepared from late stage human myeloid leukemia cells that express MNDA (HL-60) coincident with a negative reaction with the same extract prepared from a non-expressing more immature human myeloid leukemia cell line. The approach provided an efficient method for obtaining monoclonal antibodies to a specific low abundance nuclear antigen that has not been purified. Sixteen wells from three fusions contained antibody displaying a specific reaction with the nuclear protein fraction obtained from the HL-60 cells. Immunoblotting analysis revealed that all of the sixteen specific hybridoma cell lines produced antibody against the same Mr 55,000 nuclear antigen. Selecting hybridoma cells that produce antibody reactive with the native antigen provided antibody suitable for detecting MNDA in immunocytochemical tests. The rat monoclonal antibodies were purified and coupled to CNBr-activated agarose and carbonyldiimidazole-activated agarose. Although both antibody affinity matrices exhibited the same antigen binding capacities, the matrix prepared using carbonyldiimidazole-activated agarose bound the MNDA with a high level of specificity while the matrix prepared from CNBr-activated agarose bound numerous other nuclear proteins.

Isolation and characterization of monoclonal antibodies directed against plant plasma membrane and cell wall epitopes: identification of a monoclonal antibody that recognizes extensin and analysis of the process of epitope biosynthesis in plant tissues and cell cultures

Membranes from tobacco cell suspension cultures were used as antigens for the preparation of monoclonal antibodies. Use of solid phase and indirect immunofluorescence assays led to the identification of hybridomas producing antibodies directed against cell surface epitopes. One of these monoclonal antibodies (11.D2) was found to recognize a molecular species which on two-dimensional analysis (using nonequilibrium pH-gradient electrophoresis and SDS-PAGE) was found to have a high and polydisperse molecular mass and a very basic isoelectric point. This component was conspicuously labeled by [3H]proline in vivo. The monoclonal antibody cross-reacted with authentic tomato extensin, but not with potato lectin nor larch arabinogalactan. Use of the monoclonal antibody as an immunoaffinity reagent allowed the purification of a tobacco glycoprotein which was identical in amino acid composition to extensin. Finally, immunocytological analyses revealed tissue-specific patterns of labeling by the monoclonal antibody that were identical to those observed with a polyclonal antibody raised against purified extensin. We have concluded that monoclonal antibody 11.D2 recognizes an epitope that is carried exclusively by extensin. Analysis of cellular homogenates through differential and isopycnic gradient centrifugation revealed that biosynthesis of the extensin epitope was found on or within the membranes of the endoplasmic reticulum, Golgi region and plasma membrane. This result is consistent with the progressive glycosylation of the newly-synthesized extensin polypeptide during its passage through a typical eukaryotic endomembrane pathway of secretion. The 11.D2 epitope was not found in protoplasts freshly isolated from leaf tissues. However, on incubation of these protoplasts in appropriate culture media, biosynthesis of the epitope was initiated. This process was not impeded by the presence of chemicals that are reported to be inhibitors of cell wall production or of proline hydroxylation.