Rapid method for measuring ScFv thermal stability by yeast surface display

We have characterized a simplified method to determine the relative thermal stability of single-chain antibodies by following the irreversible denaturation of scFv fusions on the surface of yeast by flow cytometry. The method was highly reproducible and correlated well with other methods used to monitor thermal denaturation of the soluble proteins. We found a range of thermal stabilities for wild-type single-chain antibodies with half-maximum denaturation temperatures between 43 and 61 degrees C. The ability to quantitate thermal stability of antibodies or other proteins that are immobilized on the surface of yeast allows rapid comparisons of primary structural information with stability. Thermal denaturation could be a useful parameter to consider in the choice of scFv fragments for various applications.

Comparison of techniques for monitoring antibody fragment production in E. coli fermentation cultures

The use of an optical biosensor for monitoring antibody fragment accumulation following induction in a batch fermentation of recombinant E. coli is compared to the more traditional method of ELISA quantification. Using the biosensor, concentration data can be obtained within minutes of sample addition to the device, compared to an average assay time of 3-4 h for the ELISA. We describe two biosensor assays developed as an alternative to ELISA and compare them with ELISA in the ability to provide quantitative product accumulation profiles during fermentation. Discrepancies in titers recorded by the assays are explained by a combination of differences in product variants detected by each assay and interference from sample contaminants. Method of sample preparation is also shown to be important if accurate concentration data is required. Both biosensor assays are shown to be capable of providing product accumulation profiles comparable to those obtained by ELISA. The use of a rapid extraction technique would allow such data to be obtained during process operation, enabling improved fermentation control and more rapid process development.

Affinity-reversed-phase liquid chromatography assay to quantitate recombinant antibodies and antibody fragments in fermentation broth

An automated dual-column liquid chromatography assay comprised of affinity and reversed-phase separations that quantifies the majority of antibody-related protein species found in crude cell extracts of recombinant origin is described. Although potentially applicable to any antibody preparation, we here use samples of anti-CD18 (Fab'2LZ) and a full-length antibody, anti-tissue factor (anti-TF), from various stages throughout a biopharmaceutical production process to describe the assay details. The targeted proteins were captured on an affinity column containing an anti-light-chain (kappa) Fab antibody (AME5) immobilized on controlled pore glass. The affinity column was placed in-line with a reversed-phase column and the captured components were transferred by elution with dilute acid and subsequently resolved by eluting the reversed-phase column with a shallow acetonitrile gradient. Characterization of the resolved components showed that most antibody fragment preparations contained a light-chain fragment, free light chain, light-chain dimer and multiple forms of Fab'. Analysis of full-length antibody preparations also resolved these fragments as well as a completely assembled form. Co-eluting with the full-length antibody were high-molecular-mass variants that were missing one or both light chains. Resolved components were quantified by comparison with peak areas of similarly treated standards. By comparing the two-dimensional polyacrylamide gel electrophoresis patterns of an Escherichia coli blank run, a production run and the material affinity captured (AME5) from a production run, it was determined that the AME5 antibody captured isoforms of light chain, light chain covalently attached to heavy chain, and truncated light chain isoforms. These forms comprise the bulk of the soluble product-related fragments found in E. coli cell extracts of recombinantly produced antibody fragments.

GST fusion proteins cause false positives during selection of viral movement protein specific single chain antibodies

Glutathione S-transferase (GST) fusion proteins are used frequently for investigating protein-protein and protein-DNA interactions. The present study demonstrates that the use of GST fusion proteins caused false positives during selection of phage-displayed single-chain antibody fragments (scFvs) specific for three domains of the movement protein (NS(M)) of tomato spotted wilt virus (TSWV). To identify and exclude the false positives when using GST as a fusion partner linked to the antigen of interest, indirect phage enzyme-linked immunosorbent assay (ELISA) was compared with capture phage ELISA. Of 210 enriched phage clones, indirect phage ELISA identified 106 clones specific for binding to GST-domain fusions but not to GST. In contrast, using capture phage ELISA, all 106 selected clones were identified as false positives, reacting with the GST fusion proteins and GST. This was confirmed by characterization of soluble scFv antibodies. The data indicate that GST fusion proteins seem unsuitable for screening of phage-displayed antibody fragments and it is essential to use capture phage ELISA, instead of the indirect phage ELISA used commonly to exclude false positives in characterization of selected clones with GST fusion proteins.

Tagging bloodmeals with phagemids allows feeding of multiple-sample arrays to single cages of mosquitoes (Diptera: Culicidae) and the recovery of single recombinant antibody fragment genes from individual insects

A recombinant single-chain variable-region human antibody fragment (scFv) was expressed in Escherichia coli, extracted in hypertonic sucrose, mixed directly with blood and fed to Anopheles gambiae Giles mosquitoes. When E. coli containing the phagemids that encode these scFv were included in bloodmeals, phagemids could be recovered from the mosquito midgut for up to 3 d after feeding. Furthermore, large arrays of such gene-tagged scFv-containing bloodmeals could be fed to cages of mosquitoes using microtiter plates. Arrays of phagemids with and without an antibody insert were fed to single cages of mosquitoes to test whether individual mosquitoes fed from single wells of such arrays. Phagemids were recovered from 95% of blood-fed females and > 80% of these phagemids were monoclonal. Therefore, it is possible to feed multiple sample arrays of recombinant proteins to single cages of mosquitoes and to recover the genetic material that encodes for only one of the array elements from individual mosquitoes. This demonstration indicates that multiple-sample feeding and recovery strategies are feasible and may represent a viable strategy for future rapid screening of biologically active genes, gene products or microorganisms in live arthropods.

In vivo selection of single-chain antibodies using a yeast two-hybrid system

The current methodology for screening libraries of single-chain fragments of immunoglobulin variable domains (sFvs) utilizes bacterial phage systems. We have developed a unique in vivo selection protocol combining a modified yeast two-hybrid assay with a novel prey vector expressing sFvs. The viability of the system is demonstrated with the screen of a sFv library cloned into a yeast two-hybrid prey vector for molecules that target the bait ATF-2, a member of the CREB/ATF family of transcriptional regulatory proteins. The isolated sFv was capable of recognizing ATF-2 in vitro on Western blots and in vivo in mammalian cells.

Fasciola hepatica: parasite-secreted proteinases degrade all human IgG subclasses: determination of the specific cleavage sites and identification of the immunoglobulin fragments produced

The study was focused on the relationship of Fasciola hepatica-secreted proteinases and human IgG subclasses. Each IgG was incubated at different pH values and lengths of time with either the adult parasite excretion-secretion products or the purified cysteinyl proteinases cathepsin L1 and cathepsin L2. The Ig fragments produced were isolated and characterized by Western blot analysis, and the specific cleavage sites were determined by amino acid sequence analysis. Parasite excretion-secretion products and both cathepsins L produced similar degradation patterns and cleaved all human IgG subclasses at the hinge region, yielding at pH 7.3 and 37 degrees C Fab and Fc fragments in the case of IgG1 and IgG3 or Fab(2) and Fc in IgG2 and IgG4. While IgG1 and IgG3 were readily degraded by E/S products either in the presence or in the absence of reducing agents, IgG2 and IgG4 were resistant to proteolysis and were only digested in the presence of 0.1 M dithiothreitol. The cathepsins L needed the presence of dithiothreitol to digest IgG1, IgG2, and IgG4 whereas IgG3 was identically cleaved under both reducing and nonreducing conditions. The main cleavage sites produced by E/S products, CL1, or CL2 were located at the positions peptide bonds: His237-Thr238, Glu237-Cys239, Gly233-Asp234, and Ser241-Cys242 for gamma1, gamma2, gamma3, or gamma4, respectively. The enzymes gave additional splitting sites on the middle hinge of IgG3 to produce shorter Fc fragments and also produce Fd degradation of the IgG4. No cleavage specificity differences were found between CL1 and CL2, but they differed in the kinetics of IgG3 degradation. By lowering the pH, only the E/S products produced concomitant destruction of the Fc while preserving the Fab portion. Under all the conditions assayed the enzymes produced an Fc'-like fragment of 14-15 kDa corresponding to the whole CH3 domain of the immunoglobulin. Contrary to the extensive degradation produced by cathepsins on digested proteins, its actions on IgG subclasses were specific and restricted; thus, all the fragments produced could be potentially involved in the mechanisms used by the parasite to evade the host immune response.

Immunoglobulins of the human amniotic fluid

PROBLEM

Except for the description of a secretory immunoglobulin (S-Ig) of a low size, no recent study has investigated the molecular status of antibodies in the human amniotic fluid.

METHOD

After separation with a high performance chromatography, we analyzed the different isotypes of amniotic Igs by immunoblotting and ELISA.

RESULTS

IgG is found to be the major isotype and to contain mother-derived tetanus antitoxins. IgA is much less abundant, whereas no IgM can be detected. IgA is monomeric, with a low level of secretory IgA and with various amounts of free secretory component (SC). The presence of a low level of SC-containing immunoglobulin of a low size is confirmed during the last trimester of pregnancy. This molecule contains no alpha chain but includes a Fabgamma fragment noncovalently associated with SC. IgG, IgA, and SC are detected in the fetal urine and, therefore, can reach the amniotic fluid by this route.

CONCLUSION

In addition to the predominant maternal IgG, the amniotic fluid contains different molecular forms of fetal immunoglobulins. Their function as an immune barrier against infection and against mother-derived autoantibodies is discussed.

Active concentration measurements of recombinant biomolecules using biosensor technology

Whereas the concentration of a biomolecule simply refers to the amount of chemical substance per unit of volume, its active concentration refers to a relational parameter that has meaning only with respect to the molecule's ability to interact specifically with one particular ligand. When proteins are studied in a biological context, it is the biologically active concentration that is relevant, and not the total concentration of correctly and incorrectly folded molecules. Using a biosensor instrument the concentration of active biomolecules in a preparation can be measured by injecting the preparation at different flow rates onto a sensor chip surface presenting a high concentration of a specific ligand. The method can be used under conditions of partial mass transport limitation and does not require a pre-established standard curve. When the method was used to measure the active concentration of several recombinant proteins it was found that the active concentration was much lower than the nominal concentration determined by conventional methods. The active concentration also depended on the ligand used in the binding assay, reflecting the fact that active concentration can only be defined with respect to one specific probe. Such discrepancies in concentration values, if undetected, may lead to erroneous conclusions regarding the properties and behaviour of recombinant proteins tested in different assays.

Characterization of anti-mouse Fc gamma RII single-chain Fv fragments derived from human phage display libraries

BACKGROUND

Few antibodies are available to study the function of the Fc gamma RII murine immunoglobulin receptor. Human phage display libraries represent a potential source of single-chain Fv (sFv) to facilitate the study of the Fc gamma RII murine immunoglobulin receptor.

OBJECTIVES

To isolate human sFv specific for mouse Fc gamma RII.

STUDY DESIGN

Two human phage display libraries were selected for reactivity to mouse Fc gamma RII. Those human anti-mouse Fc gamma RII sFv that were derived from the libraries were characterized with respect to kinetics, cellular binding, epitope specificity and amino acid sequence.

RESULTS

Nine anti-mouse Fc gamma RII sFv molecules were isolated from two human phage display libraries (Marks et al., J Mol Biol 1991;222:581-597; Sheets et al., Proc Natl Acad Sci USA, in press). Surface plasmon resonance (SPR) analysis revealed that the human anti-mouse Fc gamma RII sFv had off-rates ranging from 10(-2) to 10(-3) s-1, with KD values calculated to range between 10(-7) and 10(-9) M. The binding of the FITC-labeled human anti-mouse Fc gamma RII sFv to mouse peritoneal neutrophils was not detected by flow cytometry, due to the rapid off-rates of these monomeric proteins. However, when the human anti-mouse Fc gamma RII sFv were coated on yellow-green latex particles, all of the human sFv were found to specifically bind to mouse peritoneal neutrophils. Deglycosylation of mouse Fc gamma RII did not diminish the binding of these sFv, suggesting that the sFv molecules recognize a polypeptide epitope on murine Fc gamma RII. In contrast, denaturation of mouse Fc gamma RII dramatically reduced the binding of the human sFv, suggesting that the epitopes are conformational. Sequence analysis of the human anti-mouse Fc gamma RII sFv revealed a high degree of structural similarity among the nine sFv. The DP73 VH gene segment was utilized by four of the nine sFv, while seven of the nine sFv contained the DPL16 V lambda gene segment. The sequence similarities between these sFv suggested that several of the human sFv may recognize a common epitope on mouse Fc gamma RII. Epitope mapping studies demonstrated that eight of the nine human anti-mouse Fc gamma RII sFv recognized overlapping epitopes. All of these human anti-mouse Fc gamma RII sFv competed with the 2.4G2 rat monoclonal anti-mouse Fc gamma RII/III antibody for binding with mouse Fc gamma RII, suggesting that the targeted epitopes reside in or near the Fc binding pocket of mouse Fc gamma RII.

CONCLUSIONS

The availability of novel sFv recognizing mouse Fc gamma RII will facilitate the study of receptor triggering events. Such sFv may prove useful to engage murine Fc gamma RII for targeted cytotoxicity or immunization strategies.

Selection of an scFv phage antibody that recognizes bluetongue virus from a large synthetic library and its use in ELISAs to detect viral antigen and antibodies

A filamentous phage library displaying a vast repertoire of synthetic single chain fragment variable (scFv) antibody fragments was subjected to affinity selection on purified bluetongue virus (BTV) particles. After four rounds of selection and amplification, 73 out of a total of 90 fusion phage clones tested were found to bind to purified BTV in ELISA. One of these, the clone producing the highest ELISA signal, was selected for an investigation of its potential as an immunodiagnostic reagent. The binding of this phage antibody (designated A12) could be inhibited by free virus and by antibodies in immune serum. Inhibition with antibodies in guinea-pig sera suggested that it recognized an antigenic region on BTV that was similar on at least 10 different BTV serotypes. A sandwich ELISA utilizing antibody A12 was capable of detecting approximately 60 ng of purified BTV.

Construction of mono- and bivalent human single-chain Fv fragments against the D antigen in the Rh blood group: multimerization effect on cell agglutination and application to blood typing

An expression system for mono- and bivalent single-chain Fv fragments (scFv) of a human antibody against D antigen in the Rh blood group system was established in Escherichia coli. The cDNA encoding the Fv fragment of the anti-D monoclonal antibody D10 was cloned using the polymerase chain reaction and expressed in E.coli by fusing with a peptide tag link in the C-terminus of the light chain variable region. The scFv fragment expressed by the bacteria produced specific agglutination of human D positive red cells in the presence of an anti-peptide tag antibody. Flow cytometric analysis clearly indicated that the bacterially prepared scFv showed high specificity and affinity for D antigen, which was identical with that of the parental IgG. In order to construct bivalent D10 scFv for use in direct cell agglutination, the scFv was fused with a dimeric protein, bacterial alkaline phosphatase (BAP). The fusion protein produced significant agglutination of human red blood cells with D antigen, confirming that the bacterially expressed fusion protein is a functional bivalent antibody fragment. Specific agglutination of D positive red cells by D10 scFv-BAP was enhanced in the presence of anti-BAP antibody, suggesting that further multimerization of scFv led to highly efficient cell agglutination. By grafting BAP enzymatic activity into the scFv fragment (enzyme-linked scFv), blood typing could conveniently be performed. These results indicate that bacterially expressed scFv and scFv-BAP would be of practical use in blood typing. The system reported here could also be applied to the examination of other cell surface antigens and cell agglutination.

Detection of identical Hodgkin-Reed Sternberg cell specific immunoglobulin gene rearrangements in a patient with Hodgkin's disease of mixed cellularity subtype at primary diagnosis and in relapse two and a half years later

BACKGROUND

The malignant nature of Hodgkin-Reed Sternberg (H-RS) cells has been questioned due to their scarcity in lymphoma tissues. Recently, using micromanipulation of H-RS cells and single cell PCR evidence was obtained that H-RS cells represent a clonal B-cell population. In these studies H-RS cells were isolated from each one lymph node for a given case. In classical Hodgkin's disease (HD) it thus could not be ruled out that H-RS cell clonality reflected a locally restricted clonal proliferation. We analysed biopsy specimens from a patient suffering from HD for the presence of clonally related H-RS cells at primary diagnosis and during relapse of the disease.

MATERIALS AND METHODS

In 1994 the H-RS cell line L1236 was generated from the peripheral blood of a patient suffering from a disseminating relapse of HD of mixed cellularity subtype. The patient had relapsed despite intensive treatment including high dose chemotherapy and autologous bone marrow transplantation. The clonal identity of this cell line with H-RS cells in situ was proven by amplifying identical Ig gene rearrangements of the cell line as well as of single H-RS cells picked from the patients bone marrow. Primers covering the CDR3 region were chosen from the H-RS cell specific VH1 gene rearrangement to detect H-RS cells of the identical clone by amplifying the rearranged VH1 genes in tissue samples obtained during disseminating relapsing disease and at primary diagnosis of HD in 1991.

RESULTS

The H-RS cell specific DNA sequence was detected in all affected tissues analysed including the cervical lymph node which has been exstirpated at primary diagnosis.

CONCLUSION

This finding indicates the existence of a clonal H-RS cell population during the first manifestation of HD and persistence and dissemination of this clone despite aggressive treatment. Thus, in the described case the malignant nature of H-RS cells defined by dissemination and recurrence of the identical H-RS cell clone in relapsing disease is proven.

Giant lamellar bodies in a pulmonary MALT lymphoma: a case report with ultrastructural and immunohistochemical studies

A 35-year-old, African-American man presented with a 7-year history of a persistent, enlarging pulmonary infiltrate in the right middle lobe associated with three episodes of right-sided pneumonia, recent 12-lb weight loss, and progressive shortness of breath. The nature of the right middle lobe infiltrate was unclear, but recurrent aspiration pneumonia and carcinoma of lung were important considerations. Exploratory thoracotomy with partial lobectomies revealed a low-grade B-cell lymphoma of mucosa-associated lymphoid tissue (MALT). Clusters of giant lamellar bodies were a unique finding in this lymphoma. Results of ultrastructural and immunohistochemical studies gave support to the views that these inclusions were derived from both products of cellular degeneration and surfactant. The pulmonary lymphoma subsequently spread to the gastric mucosa. The patient is alive with lymphoma 5 years after the initial diagnosis was made.

Reduction of wall adsorption in capillary zone electrophoresis of a basic single-chain antibody fragment by a cationic polymeric buffer additive

Reduction of adsorptive protein-wall interactions by poly(diallyldimethyl ammonium chloride), a permanently cationic polymer, at a concentration of 0.5% (w/v) is demonstrated for a basic single-chain antibody fragment (scFv, pI about 9.5) even in the range of physiological pH of around 7. The polymer additive forms a positively charged layer at the silica surface which reverses electroosmosis and leads to electrostatic repulsion of the positively charged basic protein.

Role of high-performance liquid chromatographic protein analysis in developing fermentation processes for recombinant human growth hormone, relaxin, antibody fragments and lymphotoxin

Development of efficient and reliable fermentation processes for protein pharmaceuticals is aided by the availability of accurate quantitative and qualitative product analyses. We have developed a variety of single and dual column chromatographic separations that meet the needs of process development and examples will be provided of how the resulting data has been used to optimize the culture process. For single column methods, reversed-phase chromatography has been the most versatile, permitting the reliable quantitation of many yeast, Chinese hamster ovary (CHO) cell and Escherichia coli-expressed products in the matrix of culture broth or cell extract. Analysis of secreted human growth hormone synthesized in E. coli, along with clipped and unprocessed forms, will be discussed. Another reversed-phase assay for direct analysis of a peptide product (B-chain relaxin) and its degradation products secreted into E. coli fermentation medium has allowed the purification of the responsible protease. Cation-exchange has proven extremely useful for the direct analysis of antibody fragment synthesized in E. coli, allowing the separation and quantitation of the desired Fab' and Fab'2, as well as the unwanted products of glutathione addition and translational read-through. Assay development is often complicated by the presence of host proteins with chromatographic behavior that is similar to that of the product. Commercial instrumentation now permits the facile development of multidimensional chromatographic assays. We show examples of coupled receptor affinity-reversed-phase assays for a mistranslation product and for covalent multimers of E. coli-synthesized lymphotoxin.

Human autoimmune anti-proteinase 3 scFv from a phage display library

This is the first study describing recombinant human antibody fragments directed to the autoantigen proteinase 3 (PR3) from an immune B cell source. Detection of these autoantibodies has proven valid for the diagnosis and monitoring of Wegener's granulomatosis. The described antibody fragment (scFv) was isolated from a phage display library prepared from the IgG-positive splenic lymphocytes of a patient with systemic autoimmunity. The cloning strategy was designed to maintain the diversity of the antibody variable gene repertoire, and sequencing of several variable genes demonstrated that all major heavy and light chain families were represented. We found an over-representation of particular heavy chain variable domains in splenic lymphocytes which differ from the ones frequently found in peripheral blood lymphocytes. It was possible to obtain specific scFv to PR3 after a single round of selection and the binding could be inhibited by the patients' sera. Although the antibody fragments in the splenic repertoire were found to be highly mutated, it was interesting to find that the selected scFv showed only limited somatic mutation. Furthermore, we could demonstrate that the removal of the mutations had no effect on binding specificity.

Thiolations, 99mTc labelings, and animal in vivo biodistributions of divalent monoclonal antibody fragments

A number of divalent monoclonal antibody fragments have been derivatized with a bifunctional reagent containing a latent thiol group, and the conjugates were thiol-deprotected by exposure to aqueous hydroxylamine. This two-step procedure enabled convenient 99mTc labeling of thiolated MAb divalent fragments, using either performed 99mTc-glucoheptonate or [99mTc] pertechnetate and single-vial lyophilized formulations of the conjugate and tin. Nonspecific incorporation of radiolabel was negligible, if any, when using nonthiolated antibodies. In animal biodistributions, in nude mice bearing LS174T human colon carcinoma xenografts, the 99mTc-labeled MAb divalent fragments studied were found to result in a 3-fold reduction in the kidney uptake of radioactivity at 24 h, compared to a 99mTc-Fab, and also to lead to improvements in other tumor:nontumor ratios.

Site-specific glycosylation of human immunoglobulin G is altered in four rheumatoid arthritis patients

Alterations in the glycosylation of human IgG have been shown to occur in rheumatoid arthritis (RA). However, the precise nature and location of these changes have not been fully established. Therefore we carried out a detailed analysis of the oligosaccharides chemically released from intact human serum IgG and fragments of the molecule. Serum samples were from three healthy ('normal') individuals, and from four patients with RA. Site-specific glycolsylation of the glycoprotein was shown to occur, which extended to sites even within the Fab fragment. These were differences in galactosylation, sialylation and the presence of a bisecting N-acetylglucosomide. Disease related alterations were also shown to be site-specific. In particular, an increase in the proportion of agalactosylated oligosaccharides occurred on the Fc fragment in RA (P=0.057), but, in contrast to previous reports there was an increase on the light chain in the proportion of fully galactosylated, bisected and core fucosylated oligosaccharides (from 13% of total in normal to between 18 and 35% in RA, P=0.057)). There was also an Fab-specific increase in oligosaccharides bearing a bisecting N-acetylglucosamine and a core fucose (P=0.075) The site-specific glycosylation changes described in this paper reveal the complexity of the regulatory mechanism, perhaps reflecting the many levels at which regulation can occur.

Abundant tyrosine residues in the antigen binding site in anti-osteosarcoma monoclonal antibodies TP-1 and TP-3: Application to radiolabeling

The variable (V) genes of TP-1 and TP-3 MAbs have been cloned and sequenced. Because of the potential use of these antibodies in the diagnosis and treatment of osteosarcoma, it is important to determine the presence and position of amino acid residues that may react with radiolabeling within the V domains. In this article, location of the tyrosine residues is determined using the knowledge of immunoglobulin structures in general. The TP-1V domains have a total of 19 tyrosines, whereas TP-3V domains have 18, with approximately half of these located within complementarity determining regions (CDRs). Thus, if equal reactivity of all tyrosines is assumed, smaller fragments of MAbs have a high probability of being radiolabeled at one of these sites with possible resultant loss of antigen binding.

Rapid Ca2+ mobilization in single LGL cells upon interaction with K562 target cells--role of the CD18 and CD16 molecules

Changes in the intracellular Ca2+ levels of human large granular lymphocytes (LGL), loaded with the fluorescent Ca2+ indicator fura-2, have been studied upon addition of human chronic myelogenous leukemia K562 cells. The measurements, analyzed at the single-cell level using image analysis, indicate a rapid Ca2+ mobilization in the effector cell upon interaction with its target cell. This mobilization appeared to be localized to an area within the effector cell that was in physical contact with target cells. The LGL responded with different kinetics in a transient manner and about 19% of them could undergo two or more responses. Data obtained from experiments performed with anti-CD16- and anti-CD18-pretreated LGL in the presence of target cells indicate that the CD16 and CD18 molecules are not likely to be the triggers of the Ca2+ response, although they might participate in the recognition of the target cell.

Cloning, expression and characterization of a single-chain antibody fragment to the herbicide paraquat

New cost effective methods for the detection and removal of pesticides from water samples are required to meet modern safety standards. The recent development of techniques to produce antibody fragments in bacteria has provided the opportunity to exploit antibodies as specialized chemicals for affinity detection/removal technologies. The variable heavy and light polypeptide chains of the anti-paraquat monoclonal antibody PQXB1/2 have been cloned into the single-chain antibody (ScAb) expression vector pBG1. The construct was expressed in Escherichia coli and 0.4 mg functional antibody produced from 1 dm3 of induced culture. Characterization of ScAb by antigen binding profile and competition ELISA showed it to have a sensitivity one order of magnitude below that of the parent monoclonal. ScAb was purified as a monomer or dimer and analysed by HPLC size exclusion chromatography. When immobilized on polystyrene beads the ScAb could remove 85% of a paraquat-bovine serum albumin conjugate from solution in a single step.

An improved affinity tag based on the FLAG peptide for the detection and purification of recombinant antibody fragments

The commercially available monoclonal antibodies M1 and M2 were raised against and bind the FLAG sequence DYKDDDDK with high specificity. Using the calcium-dependent M1 antibody and the FLAG tag attached to the N terminus of various fragments of the antibody McPC603 expressed in Escherichia coli, we found that the M1 antibody binds with almost the same affinity to a much shorter version of this sequence (DYKD). Since most antibody light chains start with an aspartate, the addition of only three additional amino acids to the N terminus is sufficient to detect and quantify the expressed antibody fragments using standard immunological methods. Similarly, the heavy chain can be detected specifically with the sequence DYKD, which requires four additional amino acids since most heavy chains do not start with Asp. The signal sequence of both chains that is necessary for the transport of the chains to the periplasm of E. coli is processed correctly. Furthermore, we investigated the influence of the amino acid at the fifth position of the FLAG sequence on the binding affinity of the M1 antibody and found that a glutamate at this position increased the sensitivity in Western blots sixfold over the original long FLAG sequence containing an aspartate residue at this position. Together, the improved FLAG is a versatile tool for both sensitive detection and one-step purification of recombinant proteins.

Characterisation of a recombinant Fv fragment of anti-MUC1 antibody HMFG1

A recombinant Fv (variable fragment) has been produced for the murine monoclonal antibody HMFG1. This antibody was raised against human milk fat globules and reacts with an epitope (PDTR) in the protein core of MUC1 mucins, which are up-regulated in human breast and other carcinomas. Binding specificity of the Fv fragment has been demonstrated through immunoaffinity purification, and by radioimmunoassay. The affinity constants for this Fv fragment and for the proteolytically produced Fab (antigen binding fragment) of the related humanised antibody HuHMFG1 were determined by monitoring the fluorescence quenching of the antibody fragments whilst adding aliquots of MUC1 related antigenic peptides KAPDTRPAPG and VTSAPDTRPAPG. Using these techniques it has been demonstrated that the products of these different methods of antibody fragmentation are comparable, and suitable for solution structure analysis using nuclear magnetic resonance (NMR) spectroscopy.