Structure-based Development of Human Interleukin-1β-Specific Antibody That Simultaneously Inhibits Binding to Both IL-1RI and IL-1RAcP

Interleukin-1β (IL-1β) is a potent pleiotropic cytokine playing a central role in protecting cells from microbial pathogen infection or endogenous stress. After it binds to IL-1RI and recruits IL-1 receptor accessory protein (IL-1RAcP), signaling culminates in activation of NF-κB. Many pathophysiological diseases have been attributed to the derailment of IL-1β regulation. Several blocking reagents have been developed based on two mechanisms: blocking the binding of IL-1β to IL-1RI or inhibiting the recruitment of IL-1RAcP to the IL-1β initial complex. In order to simultaneously fulfill these two actions, a human anti-IL-1β neutralizing antibody IgG26 was screened from human genetic phage-display library and furthered structure-optimized to final version, IgG26AW. IgG26AW has a sub-nanomolar binding affinity for human IL-1β. We validated IgG26AW-neutralizing antibodies specific for IL-1β in vivo to prevent human IL-1β-driving IL-6 elevation in C56BL/6 mice. Mice underwent treatments with IgG26AW in A549 and MDA-MB-231 xenograft mouse cancer models have also been observed with tumor shrank and inhibition of tumor metastasis. The region where IgG26 binds to IL-1β also overlaps with the position where IL-1RI and IL-1RAcP bind, as revealed by the 26-Fab/IL-1β complex structure. Meanwhile, SPR experiments showed that IL-1β bound by IgG26AW prevented the further binding of IL-1RI and IL-1RAcP, which confirmed our inference from the result of protein structure. Therefore, the inhibitory mechanism of IgG26AW is to block the assembly of the IL-1β/IL-1RI/IL-1RAcP ternary complex which further inhibits downstream signaling. Based on its high affinity, high neutralizing potency, and novel binding epitope simultaneously occupying both IL-1RI and IL-1RAcP residues that bind to IL-1β, IgG26AW may be a new candidate for treatments of inflammation-related diseases or for complementary treatments of cancers in which the role of IL-1β is critical to pathogenesis.

Refinement of immunizing antigens to produce functional blocking antibodies against the AniA nitrite reductase of Neisseria gonorrhoeae

The emergence of multi-drug resistant Neisseria gonorrhoeae has generated an urgent need for novel therapies or a vaccine to prevent gonococcal disease. In this study we investigate the potential of targeting the surface exposed nitrite reductase, AniA, to block activity by producing functional blocking antibodies. AniA activity is essential for anaerobic growth and biofilm formation of N. gonorrhoeae and functional blocking antibodies may prevent colonisation and disease. Seven peptides covering regions adjacent to the active site were designed based on the AniA structure. Six of the seven peptide conjugates generated immune responses. Peptide 7, GALGQLKVEGAEN, was able to elicit antibodies capable of blocking AniA activity. Antiserum raised against the peptide 7 conjugate detected AniA in 20 N. gonorrhoeae clinical isolates. Recombinant AniA protein antigens were also assessed in this study and generated high-titre, functional blocking antibody responses. Peptide 7 conjugates or truncated recombinant AniA antigens have potential for inclusion in a vaccine against N. gonorrhoeae.

Structural insight into allosteric modulation of protease-activated receptor 2

Protease-activated receptors (PARs) are a family of G-protein-coupled receptors (GPCRs) that are irreversibly activated by proteolytic cleavage of the N terminus, which unmasks a tethered peptide ligand that binds and activates the transmembrane receptor domain, eliciting a cellular cascade in response to inflammatory signals and other stimuli. PARs are implicated in a wide range of diseases, such as cancer and inflammation. PARs have been the subject of major pharmaceutical research efforts but the discovery of small-molecule antagonists that effectively bind them has proved challenging. The only marketed drug targeting a PAR is vorapaxar, a selective antagonist of PAR1 used to prevent thrombosis. The structure of PAR1 in complex with vorapaxar has been reported previously. Despite sequence homology across the PAR isoforms, discovery of PAR2 antagonists has been less successful, although GB88 has been described as a weak antagonist. Here we report crystal structures of PAR2 in complex with two distinct antagonists and a blocking antibody. The antagonist AZ8838 binds in a fully occluded pocket near the extracellular surface. Functional and binding studies reveal that AZ8838 exhibits slow binding kinetics, which is an attractive feature for a PAR2 antagonist competing against a tethered ligand. Antagonist AZ3451 binds to a remote allosteric site outside the helical bundle. We propose that antagonist binding prevents structural rearrangements required for receptor activation and signalling. We also show that a blocking antibody antigen-binding fragment binds to the extracellular surface of PAR2, preventing access of the tethered ligand to the peptide-binding site. These structures provide a basis for the development of selective PAR2 antagonists for a range of therapeutic uses.

Structure of malaria invasion protein RH5 with erythrocyte basigin and blocking antibodies

Invasion of host erythrocytes is essential to the life cycle of Plasmodium parasites and development of the pathology of malaria. The stages of erythrocyte invasion, including initial contact, apical reorientation, junction formation, and active invagination, are directed by coordinated release of specialized apical organelles and their parasite protein contents. Among these proteins, and central to invasion by all species, are two parasite protein families, the reticulocyte-binding protein homologue (RH) and erythrocyte-binding like proteins, which mediate host-parasite interactions. RH5 from Plasmodium falciparum (PfRH5) is the only member of either family demonstrated to be necessary for erythrocyte invasion in all tested strains, through its interaction with the erythrocyte surface protein basigin (also known as CD147 and EMMPRIN). Antibodies targeting PfRH5 or basigin efficiently block parasite invasion in vitro, making PfRH5 an excellent vaccine candidate. Here we present crystal structures of PfRH5 in complex with basigin and two distinct inhibitory antibodies. PfRH5 adopts a novel fold in which two three-helical bundles come together in a kite-like architecture, presenting binding sites for basigin and inhibitory antibodies at one tip. This provides the first structural insight into erythrocyte binding by the Plasmodium RH protein family and identifies novel inhibitory epitopes to guide design of a new generation of vaccines against the blood-stage parasite.

Identification of Peptidyl Mimics of Bioactive Gibberellin Recognized by an Antibody

We screened a phage display peptide library for peptidyl mimotopes of gibberellin against anti-bioactive gibberellin antibody. The peptides obtained were grouped into two homologous sequences and their binding to the antibody was put in competition with free GA(4) but not with GA(4) methylester, suggesting that the peptides behave as mimics of GA(4). As an application, the phage display peptide was shown to work as a tracer for enzyme-linked immunosorbent assay (ELISA) analysis of GA(4).

Fully human antibodies against the Protease-Activated Receptor-2 (PAR-2) with anti-inflammatory activity

PAR-2 belongs to a family of G-protein coupled Protease-Activated Receptors (PAR) which are activated by specific proteolytic cleavage in the extracellular N-terminal region. PAR-2 is activated by proteases such as trypsin, tryptase, proteinase 3, factor VIIa, factor Xa and is thought to be a mediator of inflammation and tissue injury, where elevated levels of proteases are found. Utilizing the HuCAL GOLD® phage display library we generated fully human antibodies specifically blocking the protease cleavage site in the N-terminal domain. In vitro affinity optimization resulted in antibodies with up to 1000-fold improved affinities relative to the original parental antibodies with dissociation constants as low as 100 pM. Corresponding increases in potency were observed in a mechanistic protease cleavage assay. The antibodies effectively inhibited PAR-2 mediated intracellular calcium release and cytokine secretion in various cell types stimulated with trypsin. In addition, the antibodies demonstrated potent inhibition of trypsin induced relaxation of isolated rat aortic rings ex vivo. In a short term mouse model of inflammation, the trans vivo DTH model, anti-PAR-2 antibodies showed inhibition of the inflammatory swelling response. In summary, potent inhibitors of PAR-2 were generated which allow further assessment of the role of this receptor in inflammation and evaluation of their potential as therapeutic agents.

Specificity tuning of antibody fragments to neutralize two human chemokines with a single agent

Chemokines are important mediators of the immune response that are responsible for the trafficking of immune cells between lymphoid organs and migration towards sites of inflammation.Using phage display selection and a functional screening approach, we have isolated a panel of single-chain fragment variable (scFv) capable of neutralizing the activity of the human chemokine CXCL10 (hCXCL10). One of the isolated scFv was weakly cross-reactive against another human chemokine CXCL9,but was unable to block its biological activity. We diversified the complementarity determining region 3 (CDR3) of the light chain variable domain (VL) of this scFv and combined phage display with high throughput antibody array screening to identify variants capable of neutralizing both chemokines. Using this approach it is therefore possible to engineer pan-specific antibodies that could prove very useful to antagonize redundant signaling pathways such as the chemokine signaling network.

Rapid isolation of intrabody candidates by using an optimized non-immune phage antibody library

Phage antibody library is a promising tool for rapidly creating in vitro single-chain Fv (scFv) antibodies to various antigens. The scFv can also act like a subcellularly-expressed antibody, known as intrabody, and can either be used as a novel research tool or used efficiently for targeted molecular therapy. However, there are only a few existing reports about the successful expression of scFvs as functional antibodies in the cell, mainly because poor quality scFv phage antibody libraries were used to isolate the intrabody clones. The aim of this study was to isolate intrabody-forming scFv clones from the nonimmune scFv phage antibody library we have generated. Using this library, we isolated a scFv clone against the apoptosis-related intracellular protein Bid in two weeks. To evaluate the intrabody-forming quality of this anti-Bid scFv clone, we expressed it in cultured mammalian cells after fusing it with the fluorescent protein Venus. The expression of the soluble form of anti-Bid scFv-Venus fusion protein was confirmed by fluorescence microscopy analysis. These results show that our scFv phage library is not only optimized for antibody production but can also be used to efficiently generate intrabodies.

A synthetic camel anti-lysozyme peptide antibody (peptibody) with flexible loop structure identified by high-resolution affinity mass spectrometry

We describe the synthesis and characterisation of the fully functional molecular recognition structure of a 26-amino acid residue peptide antibody, referred to as peptibody, designed from a monoclonal single-domain antibody fragment derived from a camel heavy-chain antibody. The CDR3 region (CDR = complementarity determining region) of the cAbLys3 camel antibody fragment, which binds to the active site of hen eggwhite lysozyme (HEL) and acts as a potent enzyme inhibitor by mimicking an oligosaccharide substrate, was prepared by solid-phase peptide synthesis. To obtain a closed loop-like structure resembling that in the crystal structure, N- and C-terminal cysteine residues were added to the linear peptide and oxidised to a cyclic disulfide-bridged peptide by using dimethylsulfoxide. A further, internal cysteine-12 residue was acetamidomethyl-protected to prevent possible oxidative byproducts. Affinity separation on a lysozyme microcolumn combined with MALDI-TOF mass spectrometry revealed that the peptide resumed high affinity to lysozyme only after deprotection of Cys-12, suggesting the importance of this paratope sequence for epitope recognition. The complex of lysozyme and active peptibody was characterised directly by conducting high-resolution ESI-FTICR mass spectrometry, which provided a molecular comparison of affinities for linear and cyclic peptibodies.

Function blocking antibodies to neuropilin-1 generated from a designed human synthetic antibody phage library

Non-immune (naïve) antibody phage libraries have become an important source of human antibodies. The synthetic phage antibody library described here utilizes a single human framework with a template containing human consensus complementarity-determining regions (CDRs). Diversity of the libraries was introduced at select CDR positions using tailored degenerate and trinucleotide codons that mimic natural human antibodies. Neuropilin-1 (NRP1), a cell-surface receptor for both vascular endothelial growth factor (VEGF) and class 3 semaphorins, is expressed on endothelial cells and neurons. NRP1 is required for vascular development and is expressed widely in the developing vasculature. To investigate the possibility of function blocking antibodies to NRP1 as potential therapeutics, and study the consequence of targeting NRP1 in murine tumor models, panels of antibodies that cross-react with human and murine NRP1 were generated from a designed antibody phage library. Antibody (YW64.3) binds to the CUB domains (a1a2) of NRP1 and completely blocks Sema3A induced neuron collapse; antibody (YW107.4.87) binds to the coagulation factor V/VIII domains (b1b2) of NRP1 and blocks VEGF binding and VEGF induced cell migration. YW107.4.87 inhibits tumor growth in animal xenograft models. These antibodies have provided valuable tools to study the roles of NRP1 in vascular and tumor biology.

The antigenic determinants on HIV p24 for CD4+ T cell inhibiting antibodies as determined by limited proteolysis, chemical modification, and mass spectrometry

In the last decade, mass spectrometry has been employed by more and more researchers for identifying the proteins in a macromolecular complex as well as for defining the surfaces of their binding interfaces. This characterization of protein-protein interfaces usually involves at least one of several different methodologies in addition to the actual mass spectrometry. For example, limited proteolysis is often used as a first step in defining regions of a protein that are protected from proteolysis when the protein of interest is part of a macromolecular complex. Other techniques used in conjunction with mass spectrometry for determining regions of a protein involved in protein-protein interactions include chemical modification, such as covalent cross-linking, acetylation of lysines, hydrogen-deuterium exchange, or other forms of modification. In this report, both limited proteolysis and chemical modification were combined with several mass spectrometric techniques in efforts to define the protein surface on the HIV core protein, p24, recognized by two different monoclonal human antibodies that were isolated from HIV+ patients. One of these antibodies, 1571, strongly inhibits the CD4+ T cell proliferative response to a known epitope (PEVIPMFSALSEGATP), while the other antibody, 241-D, does not inhibit as strongly. The epitopes for both of these antibodies were determined to be discontinuous and localized to the N-terminus of p24. Interestingly, the epitope recognized by the strongly inhibiting antibody, 1571, completely overlaps the T cell epitope PEVIPMFSALSEGATP, while the antibody 241-D binds to a region adjacent to the region of p24 recognized by the antibody 1571. These results suggest that, possibly due to epitope competition, antibodies produced during HIV infection can negatively affect CD4+ T cell-mediated immunity against the virus.

Optimization of anti-tumor necrosis factor-alpha single chain Fv displayed on phages for creation of functional antibodies

In this study, we converted the immunoglobulin-type anti-human tumor necrosis factor-alpha (TNF-alpha) monoclonal antibody (Mab) to a scFv-type antibody in order to assess its basic properties. The immunoglobulin VH and VL genes were isolated from the hybridoma that produced an anti-TNF-alpha neutralizing Mab, and they were then linked together to create scFvs of the VL-VH or VH-VL-form. The binding affinity to TNF-a was retained in both scFvs. Interestingly, the VL-VH-type scFv effectively inhibited the TNF-alpha-mediated cytotoxicity, while this neutralization activity was dramatically decreased in the VH-VL-type scFv. These results suggest that the VL-VH-type scFv is a suitable template to create improved versions of the anti-TNF-alpha antibody using a phage display system, and they also show that the structural format must be taken into account in manufacturing scFvs.

Production of Soluble and Active Transferrin Receptor-Targeting Single-Chain Antibody using Saccharomyces cerevisiae

PURPOSE

This study describes the soluble production, purification, and functional testing of an anti-transferrin receptor single-chain antibody (OX26 scFv) using the yeast Saccharomyces cerevisiae.

METHODS

The yeast secretion apparatus was optimized by modulating expression temperature, the folding environment of the endoplasmic reticulum, and gene dosage. Secreted scFv was purified using immobilized metal affinity chromatography, and tested for binding and internalization into the RBE4 rat brain endothelial cell line.

RESULTS

Secretion of OX26 scFv was optimal when expression was induced at 20 degrees C. Co-overexpression of heavy chain binding protein and protein disulfide isomerase elevated scFv expression levels by 10.4 +/- 0.3-fold. Optimization of scFv gene dosage increased secretion by 7.1 +/- 0.2-fold, but the overall benefits of binding protein and protein disulfide isomerase overexpression were diminished. Purified OX26 scFv yields of 0.5 mg/L secreted protein were achieved, and the scFv was actively internalized into RBE4 cells with a pattern similar to that observed with intact OX26 monoclonal antibody.

CONCLUSIONS

The optimized S. cerevisiae expression system is amenable to production of soluble and active brain targeting OX26 scFv, and the yeast-produced scFv has potential for the targeting and delivery of small molecules, proteins, or drug carriers across the blood-brain barrier (BBB).

Use of a blocking antibody method for the flow cytometric measurement of ZAP-70 in B-CLL

BACKGROUND

In this study we developed a method to measure the amount of ZAP-70 [zeta accessory protein] in B-CLL cells without relying on the ZAP-70 expression of patient B or T cells to normalize fluorescence intensity.

METHODS

B-CLL cells were fixed with formaldehyde before surface staining with gating antibodies CD19PC5 and CD5FITC. The cells were permeabilized with saponin, and the ZAP-70 antigen was blocked in one tube with unlabeled antibody to ZAP-70 [clone 1E7.2]. Zap-70-PE was then added to this tube. ZAP-70-PE was added to a second tube without unlabeled antibody to ZAP-70. The mean fluorescence intensity of the ZAP-70 in the tube without unlabeled antibody divided by the mean fluorescence intensity of the ZAP-70 in the tube with unlabeled antibody equals the RATIO of total fluorescence to non-specific ZAP-70 fluorescence in the B-CLL cells. In a second method of analysis, a region is created in the histogram showing ZAP-70 fluorescence intensity in the tube with unlabeled antibody to ZAP-70. This region is set to 0.9% positive cells. This same region is then used to measure the % positive [%POS] ZAP-70 cells in the tube without unlabeled antibody to ZAP-70. The brighter the ZAP-70 fluorescence above the non-specific background, the higher the %POS.

RESULTS

Due to the varying amount of non-specific staining between patient B-CLL cells and other cells, the blocking antibody method yielded a more quantitative and reproducible measure of ZAP-70 in B-CLL cells than other methods, which use the ratio of B-CLL fluorescence to normal B or T-cell fluorescence. Using this improved method, ZAP-70 was determined to be negative if the RATIO was less than 2:1 and positive if the RATIO was greater than 2:1. ZAP-70 was determined to be negative if the %POS was less than 5% and positive if the %POS was greater than 5%, a cut-off value lower than previous values published, due to exclusion of non-specific staining. Both cut-offs were based upon patient specimen distribution profiling.

CONCLUSIONS

Use of a blocking antibody resulted in a robust, reproducible clinical B-CLL assay that is not influenced by the need to measure the amount of ZAP-70 in other cells. ZAP-70 results segre gate patients into indolent and aggressive groups suggested by published clinical outcomes.

Development of Antibodies and Chimeric Molecules for Cancer Immunotherapy

Monoclonal antibodies are among the most rapidly expanding class of therapeutics for cancer treatment. Monoclonal antibodies targeting non-Hodgkin's lymphoma (NHL), Her-2/neu highly expressing metastatic breast cancer, colorectal cancer, acute myelogenous leukemia, and B-cell chronic lymphocytic leukemia (CLL) have received FDA approval. Promising new targets for antibody therapy include cellular growth factor receptors, mediators of tumor-driven neo-angiogenesis, as well as host negative immunoregulatory checkpoints that impede an effective immune response to neoplasia. Antibody efficacy has been increased by genetic engineering to humanize the antibodies and to increase their effector functions including antibody dependent cellular cytotoxicity. Furthermore, antibodies have been armed with cytokines, chemotherapeutic agents, toxins, and radionuclides to augment their efficacy as tumor cytotoxic agents. As a consequence of these advances, 30 years after their first development, monoclonal antibodies have become an important standard approach for the therapy of neoplasia with 19 therapeutic monoclonal antibodies now approved by the FDA including 8 for the treatment of cancer.

Characterization of a C3a Receptor in Rainbow Trout andXenopus: The First Identification of C3a Receptors in Nonmammalian Species

Virtually nothing is known about the structure, function, and evolutionary origins of the C3aR in nonmammalian species. Because C3aR and C5aR are thought to have arisen from the same common ancestor, the recent characterization of a C5aR in teleost fish implied the presence of a C3aR in this animal group. In this study we report the cloning of a trout cDNA encoding a 364-aa molecule (TC3aR) that shows a high degree of sequence homology and a strong phylogenetic relationship with mammalian C3aRs. Northern blotting demonstrated that TC3aR was expressed primarily in blood leukocytes. Flow cytometric analysis and immunofluorescence microscopy showed that Abs raised against TC3aR stained to a high degree all blood B lymphocytes and, to a lesser extent, all granulocytes. More importantly, these Abs inhibited trout C3a-mediated intracellular calcium mobilization in trout leukocytes. A fascinating structural feature of TC3aR is the lack of a significant portion of the second extracellular loop (ECL2). In all C3aR molecules characterized to date, the ECL2 is exceptionally large when compared with the same region of C5aR. However, the exact function of the extra portion of ECL2 is unknown. The lack of this segment in TC3aR suggests that the extra piece of ECL2 was not necessary for the interaction of the ancestral C3aR with its ligand. Our findings represent the first C3aR characterized in nonmammalian species and support the hypothesis that if C3aR and C5aR diverged from a common ancestor, this event occurred before the emergence of teleost fish.

Bifunctional Peptides Derived from Homologous Loop Regions in the Laminin α Chain LG4 Modules Interact with both α2β1 Integrin and Syndecan-2

Laminin alpha chains show diverse biological functions in a chain-specific fashion. The laminin G-like modules (LG modules) of the laminin alpha chains consist of a 14-stranded beta-sheet sandwich structure with biologically active sequences found in the connecting loops. Previously, we reported that connecting loop regions between beta-strands E and F in the mouse laminin alpha chain LG4 modules exhibited chain-specific activities. In this study, we focus on the homologous loop regions in human laminin alpha chain LG4 modules using five synthetic peptides (hEF-1-hEF-5). These homologous peptides induced chain-specific cellular responses in various cell types. Next, to examine the dual-receptor recognition model, we synthesized chimeras (cEF13A-cEF13E) derived from peptides hEF-1 and hEF-3. All of the chimeric peptides promoted fibroblast attachment as well as the parental peptides. Attachment of fibroblasts to cEF13A and cEF13B was inhibited by anti-integrin alpha2 and beta1 antibodies and by heparin, while cell adhesion to cEF13C, cEF13D, and cEF13E was blocked only by heparin. Actin organization of fibroblasts on cEF13C was not different from that on hEF-3, but cEF13B induced membrane ruffling at the tips of the actin stress fibers. These results suggest that cEF13B had bifunctional effects on cellular behaviors through alpha2beta1 integrin and heparin/heparan sulfate proteoglycan. We conclude that the approach utilizing chimeric peptides is useful for examining cellular mechanisms in dual-receptor systems.

N-terminal residues of the chemotaxis inhibitory protein of Staphylococcus aureus are essential for blocking formylated peptide receptor but not C5a receptor

Staphylococcus aureus excretes a factor that specifically and simultaneously acts on the C5aR and the formylated peptide receptor (FPR). This chemotaxis inhibitory protein of S. aureus (CHIPS) blocks C5a- and fMLP-induced phagocyte activation and chemotaxis. Monoclonal anti-CHIPS Abs inhibit CHIPS activity against one receptor completely without affecting the other receptor, indicating that two distinct sites are responsible for both actions. A CHIPS-derived N-terminal 6 aa peptide is capable of mimicking the anti-FPR properties of CHIPS but has no effect on the C5aR. Synthetic peptides in which the first 6 aa are substituted individually for all other naturally occurring amino acids show that the first and third residue play an important role in blocking the FPR. Using an Escherichia coli expression system, we created mutant CHIPS proteins in which these amino acids are substituted. These mutant proteins have impaired or absent FPR- but still an intact C5aR-blocking activity, indicating that the loss of the FPR-blocking activity is not caused by any structural impairment. This identifies the first and third amino acid, both a phenylalanine, to be essential for CHIPS blocking the fMLP-induced activation of phagocytes. The unique properties of CHIPS to specifically inhibit the FPR with high affinity (kd=35.4 +/- 7.7 nM) could be an important new tool to further stimulate the fundamental research on the mechanisms underlying the FPR and its role in disease processes.

PPARalpha activators down-regulate CYP2C7, a retinoic acid and testosterone hydroxylase

Peroxisome proliferators (PP) are a large class of structurally diverse chemicals that mediate their effects in the liver mainly through the peroxisome proliferator-activated receptor alpha (PPARalpha). Exposure to PP results in down-regulation of CYP2C family members under control of growth hormone and sex steroids including CYP2C11 and CYP2C12. We hypothesized that PP exposure would also lead to similar changes in CYP2C7, a retinoic acid and testosterone hydroxylase. CYP2C7 gene expression was dramatically down-regulated in the livers of rats treated for 13 weeks by WY-14,643 (WY; 500 ppm) or gemfibrozil (GEM; 8000 ppm). In the same tissues, exposure to WY and GEM and to a lesser extent di-n-butyl phthalate (20,000 ppm) led to decreases in CYP2C7 protein levels in both male and female rats. An examination of the time and dose dependence of CYP2C7 protein changes after PP exposure revealed that CYP2C7 was more sensitive to compound exposure compared to other CYP2C family members. Protein expression was decreased after 1, 5 and 13 weeks of PP treatment. CYP2C7 protein expression was completely abolished at 5 ppm WY, the lowest dose tested. GEM and DBP exhibited dose-dependent decreases in CYP2C7 protein expression, becoming significant at 1000 ppm or 5000 ppm and above, respectively. These results show that PP exposure leads to changes in CYP2C7 mRNA and protein levels. Thus, in addition to known effects on steroid metabolism, exposure to PP may alter retinoic acid metabolism.

Activity and safety of CTLA-4 blockade combined with vaccines in cynomolgus macaques

The immune modulatory molecule CTLA-4 (CD152), through interactions with the B7 costimulatory molecules, has been shown to be a negative regulator of T cell activation in various murine model systems. Abs that block CTLA-4 function can enhance immune responses that mediate potent antitumor activity. However, CTLA-4 blockade can also exacerbate autoimmune disease. The safety and activity of anti-CTLA-4 Abs in primates has not been addressed. To that end, we generated human Abs against CTLA-4 using transgenic mice expressing human Ig genes. A high affinity Ab (10D1) that blocked the binding of CTLA-4 to the B7-1 and B7-2 ligands and had cross-reactivity with macaque CTLA-4 was chosen for further development. Administration of 10D1 to cynomolgus macaques significantly enhanced Ab responses to hepatitis surface Ag and a human melanoma cell vaccine. Anti-self Ab responses as measured by immunoassays using lysate from melanocyte-rich tissues were elicited in those animals receiving the melanoma cell vaccine and anti-CTLA-4 Ab. Remarkably, chronic administration of 10D1 did not result in measurable polyclonal T cell activation, significant alteration of the lymphocyte subsets, or induce clinically observable autoimmunity. Repeated dosing of the 10D1 did not elicit monkey anti-human Ab responses in the monkeys. These observations support the development of CTLA-4 blockade for human immunotherapy.

Physical-chemical features of non-detergent sulfobetaines active as protein-folding helpers

Some non-detergent sulfobetaines had been shown to prevent aggregation and improve the yield of active proteins when added to the buffer during in vitro protein renaturation. With the aim of designing more efficient folding helpers, a series of non-detergent sulfobetaines have been synthesized and their efficiency in improving the renaturation of a variety of proteins (E. coli tryptophan synthase and beta-D-galactosidase, hen lysozyme, bovine serum albumin, a monoclonal antibody) have been investigated. Attempts to correlate the structure of each sulfobetaines with its effect on folding revealed some molecular features that appear important in helping renaturation. This enabled us to design and synthesize new non-detergent sulfobetaines that act as potent folding helpers.

Identification of tissue transglutaminase as a novel molecule involved in human CD8+ T cell transendothelial migration

During inflammation, T lymphocytes migrate out of the blood across the vascular endothelium in a multistep process. The receptors mediating T cell adhesion to endothelium are well characterized; however, the molecules involved in T cell transendothelial migration (TEM) subsequent to lymphocyte adhesion to the endothelium are less clear. To identify receptors mediating TEM, mAbs were produced against human blood T cells adhering to IFN-gamma-activated HUVEC in mice and tested for inhibition of lymphocyte TEM across cytokine-activated HUVEC. Most of the mAbs were against beta(1) and beta(2) integrins, but one mAb, 6B9, significantly inhibited T cell TEM across IFN-gamma, TNF-alpha, and IFN-gamma plus TNF-alpha-stimulated HUVEC, and did not react with an integrin. 6B9 mAb did not inhibit T cell adhesion to HUVEC, suggesting that 6B9 blocked a novel pathway in T cell TEM. The 6B9 Ag was 80 kDa on SDS-PAGE, and was expressed by both blood leukocytes and HUVEC. Immunoaffinity purification and mass spectrometry identified this Ag as tissue transglutaminase (tTG), a molecule not known to mediate T cell TEM. Treatment of HUVEC with 6B9 was more effective than treatment of T cells. 6B9 blockade selectively inhibited CD4(-), but not CD4(+), T cell TEM, suggesting a role for tTG in recruitment of CD8(+) T lymphocytes. Thus, 6B9 is a new blocking mAb to human tTG, which demonstrates that tTG may have a novel role in mediating CD8(+) T cell migration across cytokine-activated endothelium and infiltration of tissues during inflammation.

IL-18 receptor beta-induced changes in the presentation of IL-18 binding sites affect ligand binding and signal transduction

IL-18 is a pleiotropic proinflammatory cytokine that is involved in induction of inflammatory mediators, regulation of the cytotoxic activity of NK cells and T cells, and differentiation and activation of both Th1 and Th2 cells. IL-18 signals through its specific cell surface receptor IL-18R, which comprises two subunits: IL-18R alpha and IL-18R beta. IL-18R alpha alone has a weak affinity for IL-18 binding, while the IL-18R alpha/beta complex has a high affinity. By using several anti-IL-18 mAbs and IL-18 binding protein, we have examined whether these site-specific inhibitors could block the binding of IL-18 to IL-18R alpha and to the IL-18R alpha/beta complex. Here we show that IL-18 binding to IL-18R alpha was inhibited by a neutralizing mAb, 125-2H, while binding of IL-18 to the alpha/beta receptor complex was not. This suggests that IL-18R beta-induced conformational changes may occur in IL-18R alpha upon dimerization, leading to changes in the presentation of IL-18 binding sites. Epitope mapping of 125-2H using human-mouse IL-18 chimeras identified a region in IL-18 that was required for 125-2H recognition. This region, as examined by IL-18R binding and functional analysis, appeared to be critical for triggering signal transduction through the heterodimeric receptor.

Molecular cloning and chimerisation of an inhibitory anti-cathepsin B antibody and its expression in Chinese hamster ovary cells

The lysosomal cysteine protease cathepsin B is one of several proteases that have been linked to tumour progression. Its increased expression and secretion in tumour cells may facilitate the degradation of extracellular matrix proteins, leading to tumour cell invasion and metastasis. Specific inhibitory monoclonal antibodies are a possible alternative to synthetic inhibitors as a therapeutic tool for cancer treatment. An inhibitory monoclonal antibody, which binds to an epitope near the active site of cathepsin B and inhibits its proteolytic activity, was prepared and its effect on invasion of ras-transformed MCF-10A neoT cells was tested in vitro. Here we present the nucleotide sequences of the heavy and light chains of the inhibitory antibody and compare them to the murine immunoglobulin germline sequences for possible somatic hypermutations. Since no harmful mutations were found, a mouse/human chimeric antibody was constructed by fusing murine V(H) and V(L) variable regions of the inhibitory antibody with human gamma 1 and K constant regions, respectively. Chinese hamster ovary K1 cells were co-transfected with expression vectors pcD-NA3L and pcDNA3H and the reactivity of the isolated chimeric antibody was tested by ELISA and Western blotting. We could demonstrate an inhibitory effect of the chimeric antibody.

Identification of the interface of a large protein-protein complex using H/D exchange and Fourier transform ion cyclotron resonance mass spectrometry

An infrared multiphoton dissociation (IRMPD) spectrum, obtained by Fourier transform ion cyclotron resonance mass spectrometry (FTICRMS), was used to dissociate and to identify fragment ions from recombinant human interleukin-6 (IL-6; 21 KDa). The entire sequence was assigned by a single IRMPD experiment, and the observed fragment ions reflected the IL-6 secondary structure. This method was combined with H/D off-exchange to identify IL-6 and anti-human IL-6 mouse monoclonal antibody MH166 (150-kDa) binding sites in the IL-6 molecule. To facilitate the data analysis, the protein complex formation and the hydrogen exchange were performed with an immobilized antibody. Quenching of the hydrogen exchange reaction and collection of the deuterated IL-6 were performed by elution under acidic conditions to measure the mass spectrum directly. IL-6 was dissociated by using IRMPD, and the interface of IL-6 bound to anti-IL-6 antibody MH166 was determined to analyze the deuterium incorporation level of each fragment ion. Thus, two discontinuous regions, Leu 126-Lys 131 and Asp 160-Met 184, were identified as the antibody binding sites. These regions are adjacent to each other on the tertiary structures determined by NMR and X-ray analyses.

Modulating pharmacokinetics of an anti-interleukin-8 F(ab')(2) by amine-specific PEGylation with preserved bioactivity

By covalently attaching biocompatible polyethylene-glycol (PEG) groups to epsilon-amino groups of the F(ab')(2) form of a humanized anti-interleukin-8 (anti-IL-8) antibody, we sought to decrease the in vivo clearance rate to give a potentially more clinically acceptable therapeutic. The in vivo clearance was modulated by changing the hydrodynamic size of the PEGylated antibody fragments. To achieve significant increases in the hydrodynamic size with minimal loss in bioactivity, high molecular weight linear or branched PEG molecules were used. Modification involved N-hydroxy-succinamide reaction of the PEGs with primary amines (lysines and/or the N-terminus) of the anti-IL-8 F(ab')(2). The process of adding up to four linear 20 kDa PEG, or up to two branched 40 kDa PEG, gave reproducible distribution of products. The components with uniform size (as assessed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis) were purified by a single-step ion-exchange high-performance liquid chromatography and showed no significant loss of biological activity in ligand binding and cell-based assays. Addition of a single branched 40 kDa PEG to a F(ab')(2) (molecular weight (MW)=1.6 million Da) or up to two 40 kDa branched PEG (MW=1.9 million Da) increased the serum half-life to 48 h as compared with the unPEGylated F(ab')(2) with a half-life of 8.5 h. This study shows that by attaching high molecular weight PEGs at a one or two sites, bioactive antibody fragments can be made reproducibly with sizes tailored to achieve the desired pharmacokinetics.

CD14 employs hydrophilic regions to "capture" lipopolysaccharides

CD14 participates in the host innate inflammatory response to bacterial LPS obtained from Escherichia coli and other Gram-negative bacteria. Evidence from several laboratories suggests that different regions of the amino-terminal portion of the molecule may be involved in LPS binding. In this report a series of single-residue serine replacement and charge reversal mutations were generated to further elucidate the mechanism by which this protein may bind a multitude of different LPS ligands. Single-residue CD14 mutation proteins were examined for their ability to bind LPS obtained from E. coli, Porphyromonas gingivalis, and Helicobacter pylori and facilitate the activation of E-selectin from human endothelial cells. In addition, the single-residue CD14 mutation proteins were employed to perform monoclonal epitope-mapping studies with three LPS-blocking Abs that bound tertiary epitopes. Evidence that several different hydrophilic regions of the amino-terminal region of CD14 are involved in LPS binding was obtained. Epitope-mapping studies revealed that these hydrophilic regions are located on one side of the protein surface. These studies suggest that CD14 employs a charged surface in a manor similar to the macrophage scavenger receptor to "capture" LPS ligands and "present" them to other components of the innate host defense system.

Lymphocyte adhesion to epithelia and endothelia mediated by the lymphocyte endothelial-epithelial cell adhesion molecule glycoprotein

Upon encountering the relevant vascular bed, lymphocytes attach to endothelial adhesion molecules, transmigrate out of circulation, and localize within tissues. Lymphocytes may then be retained at microanatomic sites, as in tissues, or they may continue to migrate to the lymphatics and recirculate in the blood. Lymphocytes also interact transiently, but with high avidity, with target cells or APC that are infected with microbes or have taken up exogenous foreign Ags. This array of adhesive capabilities is mediated by the selective expression of lymphocyte adhesion molecules. Here, we developed the 6F10 mAb, which recognizes a cell surface glycoprotein designated lymphocyte endothelial-epithelial cell adhesion molecule (LEEP-CAM), that is distinct in biochemical characteristics and distribution of expression from other molecules known to play a role in lymphocyte adhesion. LEEP-CAM is expressed on particular epithelia, including the suprabasal region of the epidermis, the basal layer of bronchial and breast epithelia, and throughout the tonsillar and vaginal epithelia. Yet, it is absent from intestinal and renal epithelia. Interestingly, it is expressed also on vascular endothelium, especially high endothelial venules (HEV) in lymphoid organs, such as tonsil and appendix. The anti-LEEP-CAM mAb specifically blocked T and B lymphocyte adhesion to monolayers of epithelial cells and to vascular endothelial cells in static cell-to-cell binding assays by approximately 40-60% when compared with control mAbs. These data suggest a role for this newly identified molecule in lymphocyte binding to endothelium, as well as adhesive interactions within selected epithelia.

Development of a monoclonal antibody blocking-ELISA for detection of antibodies against Maedi-Visna virus

A monoclonal antibody (MAb) blocking ELISA (Blck-ELISA) was developed to detect antibodies against Maedi-Visna virus (MVV) in sheep sera. The assay employs a MAb directed against the envelope protein p90 of the virus in a sandwich blocking procedure. To determine whether the MAb was a potential antibody for developing a Blck-ELISA, a collection of three hundred sera obtained from several sheep flocks known to be infected with MVV were used to examine the sensitivity of the Blck-ELISA. A total of 50 serum samples originating from a flock free of MVV were tested to assess the specificity of the assay. The results were compared with a commercial indirect ELISA (I-ELISA) and samples giving a conflicting or doubtful result were tested by immunoblot. The Blck-ELISA proved to be specific, sensitive and it showed high reproducibility and low variability.

Human anti-porcine T cell response: blocking with anti-class I antibody leads to hyporesponsiveness and a switch in cytokine production

Intervention in the molecular interactions that lead to an immune response is possible at various stages of Ag recognition and T cell activation. Perturbation of the interaction of the TCR with the MHC/peptide ligand complex is one approach that has shown promise for autoimmunity and graft rejection in blocking T cell-activated responses. In this study, we investigated the effect of altering the target MHC class I molecule by blocking with Abs. We established a system that analyzed the human T cell response against MHC class I+/class II- porcine stimulatory cell targets. The primary human response against porcine smooth muscle cells was CD8+ T cell dependent. In the presence of F(ab')2 fragments of the MHC class I-reactive Ab, PT-85, the proliferative response was inhibited and production of IL-2 and IFN-gamma was blocked. Moreover, in a secondary response, proliferation was reduced and type 1 cytokine levels were inhibited. In contrast, levels of IL-10 and IL-4 were sustained or slightly increased. These findings indicate that Ab against MHC class I blocked the recognition of porcine cells by the human CD8+ T cells and altered the cytokine secretion profile. Thus, a single treatment with PT-85 F(ab')2 directed against the MHC class I molecule provides an attractive approach to the induction of T cell tolerance that may provide long-term graft survival in porcine-to-human cell transplantation.

Monoclonal antibodies to murine lipopolysaccharide (LPS)-binding protein (LBP) protect mice from lethal endotoxemia by blocking either the binding of LPS to LBP or the presentation of LPS/LBP complexes to CD14

Cellular responses to LPS, the major lipid component of the outer membrane of Gram-negative bacteria, are enhanced markedly by the LPS-binding protein (LBP), a plasma protein that transfers LPS to the cell surface CD14 present on cells of the myeloid lineage. LBP has been shown previously to potentiate the host response to LPS. However, experiments performed in mice with a disruption of the LBP gene have yielded discordant results. Whereas one study showed that LBP knockout mice were resistant to endotoxemia, another study did not confirm an important role for LBP in the response of mice challenged in vivo with low doses of LPS. Consequently, we generated rat mAbs to murine LBP to investigate further the contribution of LBP in experimental endotoxemia. Three classes of mAbs were obtained. Class 1 mAbs blocked the binding of LPS to LBP; class 2 mAbs blocked the binding of LPS/LBP complexes to CD14; class 3 mAbs bound LBP but did not suppress LBP activity. In vivo, class 1 and class 2 mAbs suppressed LPS-induced TNF production and protected mice from lethal endotoxemia. These results show that the neutralization of LBP accomplished by blocking either the binding of LPS to LBP or the binding of LPS/LBP complexes to CD14 protects the host from LPS-induced toxicity, confirming that LBP is a critical component of innate immunity.

Development and characterization of antibodies directed against the mouse D4 dopamine receptor

Polyclonal antibodies against the mouse D4 dopamine receptor have been developed in order to investigate the anatomical localization of this receptor in the mouse brain. Two antibodies were generated against specific peptides corresponding to predicted extracellular and intracellular regions of the D4 protein. Specificity of these antibodies was demonstrated on human embryonic kidney 293 (HEK 293) cells transfected with different dopamine receptor subtypes; immunoreactivity was detected only in cells transfected with the mouse D4 dopamine receptor cDNA. Following in vitro transcription/translation of the mouse D4 cDNA, a single protein band of 36 kDa was selectively immunoprecipitated with the anti-D4 antibodies. The antibodies also detected a single protein of 36 kDa in Western blot of HEK 293 cells transiently transfected with the mouse D4 receptor. These antibodies were able to detect the D4 receptor in several regions of the mouse brain. In the regions examined, D4 immunoreactivity was found in neurones located in layers II-VI of the frontal and piriform cortices, with the highest concentration in layer II; in scattered neurones in the caudate putamen and in larger neurones in the globus pallidus. In all experiments, both antibodies exhibit the same specificity, and all immunoreactivity could be abolished by preincubation with the corresponding peptide antigen.

Demonstration of fragments with thyroid stimulating activity from thyroid stimulation blocking antibodies-IgG molecules by papain digestion

OBJECTIVES

Thyroid stimulation blocking antibodies (TSBAb) inhibit TSH action and may have a role in the pathogenesis of hypothyroidism. In order to study the relationship between blocking and stimulating activities we have examined the biologically active fragments in TSBAb-IgG molecules after papain digestion.

DESIGN

Both thyroid stimulating (TS) activity (cAMP production in thyroid cells) and TSH binding inhibitory (TBI) activity (determined by TSH receptor assay) in sera from patients with primary hypothyroidism were examined after digestion with papain-Sepharose in the presence of cysteine. The digested IgG was separated into unbound (UF) and bound (BF) fractions on a Protein A-Sepharose column. Each fraction was then gel-filtrated on a Sephadex G-100 column.

RESULTS

TS activity was found within one hour after hydrolysis in 5 out of 7 antibodies, then gradually decreased after more prolonged incubation. Both TS and TBI activities in the UF and the BF from Protein A were found in Feb (Mr 50 kD) and the second protein peak (Fc with trace amounts of Fab), respectively. The biological activity in the second protein peak was suggested as being derived from Fab fraction, because the activity bound to the anti-F(ab')2 column. However, the first peak (undigested IgG) in the BF had neither TS nor TSB activity. The TS activity in the retarded fraction (less than Mr 20 kD) in the UF gradually increased with prolonged digestion.

CONCLUSIONS

The conversion of Thyroid stimulation blocking antibodies activity to thyroid stimulating activity by papain digestion suggests that the inherent thyroid stimulating activity located in the Fab portion of the IgG molecule is unmasked by papain cleavage. We also suggest that the thyroid stimulating activity in the retarded fraction in the unbound fraction may be released from hydrolysis of the Fab portion of the IgG molecule.

Interaction of chemokine receptor CCR5 with its ligands: multiple domains for HIV-1 gp120 binding and a single domain for chemokine binding

CCR5 is a chemokine receptor expressed by T cells and macrophages, which also functions as the principal coreceptor for macrophage (M)-tropic strains of HIV-1. To understand the molecular basis of the binding of chemokines and HIV-1 to CCR5, we developed a number of mAbs that inhibit the various interactions of CCR5, and mapped the binding sites of these mAbs using a panel of CCR5/CCR2b chimeras. One mAb termed 2D7 completely blocked the binding and chemotaxis of the three natural chemokine ligands of CCR5, RANTES (regulated on activation normal T cell expressed and secreted), macrophage inflammatory protein (MIP)-1alpha, and MIP-1beta, to CCR5 transfectants. This mAb was a genuine antagonist of CCR5, since it failed to stimulate an increase in intracellular calcium concentration in the CCR5 transfectants, but blocked calcium responses elicited by RANTES, MIP-1alpha, or MIP-1beta. This mAb inhibited most of the RANTES and MIP-1alpha chemotactic responses of activated T cells, but not of monocytes, suggesting differential usage of chemokine receptors by these two cell types. The 2D7 binding site mapped to the second extracellular loop of CCR5, whereas a group of mAbs that failed to block chemokine binding all mapped to the NH2-terminal region of CCR5. Efficient inhibition of an M-tropic HIV-1-derived envelope glycoprotein gp120 binding to CCR5 could be achieved with mAbs recognizing either the second extracellular loop or the NH2-terminal region, although the former showed superior inhibition. Additionally, 2D7 efficiently blocked the infectivity of several M-tropic and dual-tropic HIV-1 strains in vitro. These results suggest a complicated pattern of HIV-1 gp120 binding to different regions of CCR5, but a relatively simple pattern for chemokine binding. We conclude that the second extracellular loop of CCR5 is an ideal target site for the development of inhibitors of either chemokine or HIV-1 binding to CCR5.

A ligand for human CD48 on epithelial cells

CD48 is a member of the Ig superfamily with a high degree of sequence homology to CD58 (LFA-3). In rodents, CD48 is the ligand for CD2 whereas in humans, CD58 is the ligand for CD2. Despite intensive efforts, no ligand for human CD48 has been convincingly demonstrated. We now show that a ligand for human CD48 is present on epithelial cells. The ligand was detected based on the ability of epithelial cells to bind both a decameric, soluble CD48 IgM fusion protein and monomeric CD48 immobilized on plastic dishes. mAbs raised to the ligand completely block binding of CD48 to all epithelial cells tested. We further show that the cell surface proteoglycan CD44 plays an auxiliary role in the binding of epithelial cells to CD48 and that this interaction involves the glycosaminoglycan binding site of CD44. No interaction of human CD48 with CD2 was detected. This is the first clear demonstration that human CD48 can function as an adhesion molecule and suggests a role for CD48 in lymphocyte epithelial cell interactions.

Characterization of a novel adhesion function blocking monoclonal antibody to rat/mouse P-selectin generated in the P-selectin-deficient mouse

P-selectin is an important adhesion molecule involved in leukocyte migration. However, to date, no monoclonal antibodies (MAb) generated against rat P-selectin have been identified which block P-selectin mediated leukocyte adhesion. Most studies in the rat have utilized crossreacting antibodies generated against P-selectin in higher species. In a P-selectin deficient mouse we generated an anti-rat/mouse P-selectin MAb, designated RMP-1, by immunization with activated rat platelets. This IgG2a MAb immunoprecipitates a 140 kDa protein under reducing conditions from rat platelet lysate. By ELISA and immunofluorescence flow cytometry, MAb RMP-1 reacts with thrombin-activated but not unactivated rat platelets. In addition, by ELISA MAb RMP-1 binds to activated mouse platelets and recombinant rat and mouse P-selectin. MAb RMP-1 inhibited adhesion of HL-60 myeloid cells to immobilized mouse P-selectin by 97% and to activated rat and mouse platelets by 100% under static conditions, confirming the adhesion function blocking activity of MAb RMP-1. This novel MAb should be useful for studying P-selectin function in vitro and in vivo in both rat and mouse inflammation models.

A novel monoclonal antibody mNI-58A against the alpha-chain of leukocyte function-associated antigen-1 (LFA-1) blocks the homotypic cell aggregation and actively regulates morphological changes in the phorbol myristate acetate (PMA)-activated human monocyte-like cell line, U937

A monoclonal antibody (mAb), designated mNI-58A, was produced by immunizing mice with the lipopolysaccharide (LPS)-stimulated monocyte-like cell line, U937. The antigen defined by mNI-58A was widely expressed on various lymphoid cells and all cell lines examined except the erythroid cell line, K562. When the reactive patterns between mNI-58A and the mAbs to various human differentiation antigens (CD11a, CD11b, CD11c, CD14, CD16, CD18, CD23, CD28, CD29, CD31, CD43, CD44, CD45RA, CD50, CD54, CD58, CD80, CD102, CD106, HLA-class I and-class II antigen) were compared, that of mNI-58A was found to be similar to those of the leukocyte function-associated antigen-1 (LFA-1) mAbs. Using a competitive immunofluorescence binding assay it was found that the preincubation with one of the CD11a mAbs, 2F12 completely blocked the subsequent binding of mNI-58A. mNI-58A prevented the homotypic cell aggregation of the phorbol myristate acetate (PMA)-activated U937 cells (referred to as PMA-U937) and PMA-activated Epstein-Barr virus (EBV)-transformed B cell lines, B-85 and Mann. mNI-58A markedly induced the spread formation of the PMA-U937 cells following this blocking of the homotypic cell aggregation, whereas 2F12 did not under the same condition. The spread formation induced by mNI-58A was completely blocked by cytochalasin B (CyB), cytochalasin D (CyD), cycloheximide (CHX) or protein kinase C inhibitors, sphingosine and H-7. The U937 cells markedly adhered to the tumor necrosis factor-alpha (TNF-alpha)-stimulated human umbilical vein endothelial cells (HUVECs) and also to the extracellular matrix protein, fibronectin, but mNI-58A did not enhance or block these adhesion process. mNI-58A precipitated two glycoproteins with molecular weight 180 kDa and 95 kDa as determined by SDS-PAGE analysis, which were identical to the LFA-alpha (CD11a) and beta (CD18) chains of leukocyte integrin precipitated by the CD11a mAbs, respectively. Sequential immunoprecipitation studies using the CD11a mAb (2F12) also indicate that mNI-58A recognizes an epitope on the alpha-chain of the LFA-1 molecule. The ability of mNI-58A to block the PMA-U937 cells and to induce the spread formation of these cells suggests that mNI-58A is a novel mAb reacting with an epitope on the alpha-chain of LFA-1 different from those recognized with the existing CD11a mAbs.

An E-selectin binding assay based on a polyacrylamide-type glycoconjugate

Here we show that biotinylated polyacrylamide-type glycoconjugates which contain sialyl Lewis X (sLex-polymer) or sialyl Lewis A (sLea-polymer) are ligands for E-selectin. sLea-polymer bound E-selectin with higher affinity than sLex-polymer. Based on this property we used the sLea-polymer to establish a sensitive cell-free binding assay for the characterization of E-selectin antagonists. The assay involves complexation of the biotinylated sLea-polymer with streptavidin-peroxidase. This complex is incubated with E-selectin mouse Ckappa fusion protein immobilized onto microtiter plates. Bound complex is detected by the peroxidase reaction. sLea-polymer bound in a Ca2+-dependent manner consistent with the function of E-selectin as a C-type lectin. Control glycoconjugates with sialic acid (alpha-Neu5Ac), Lewis A (Lea), or beta-D-glucose residues instead of sLea failed to interact with the E-selectin. Neutralizing anti-E-selectin antibodies blocked completely binding to E-selectin. This demonstrates specificity of the assay system. sLex blocked binding of the sLea-polymer to E-selectin by 50% at a concentration of 550 microM (IC50). The assay was used to characterize sLea-polymers with differing sLea content as multivalent inhibitors of E-selectin binding. The inhibitory activity of these polymeric forms of sLea increased with their sLea content up to IC50s in the low micromolar range. The binding assay described is sensitive, rapid, and simple and of low variability. Therefore it should be advantageous for the identification and characterization of novel E-selectin antagonists.

Structural diversity of monoclonal CD4 antibodies and their capacity to block the HIV gp120/CD4 interaction

A number of monoclonal antibodies have been raised against CD4, the receptor on T cells for the HIV envelope glycoprotein gp120. In the present paper we describe biological activities and sequence analysis of seven CD4 MAb. Five of these MAb preparations compete with HIV/gp120 for CD4 binding. The sequences of the variable regions for these MAb were determined in order to ascertain any correlation with selective V gene usage. A relationship was found between the expressed variable region genes and the CD4 recognition pattern. The VH genes that are used can be subdivided into two major groups expressing either a VH gene belonging to the J558 family or to the VGam family. The usage of the VL genes varies, indicating that the epitope specificity is predominantly determined by the rearranged VH genes. The distinct cross-reactivity pattern of these MAb also correlates with their capacity to block binding of recombinant gp120 to CD4 in vitro. Although five of these MAb were able to block gp120 binding none of the CDR sequences shows a relevant homology to the gp120 sequence. This indicates a steric hinderence mechanism for blocking gp120 binding and not a direct interaction with the receptor binding site on CD4. The data also confirm the failure of these MAb as a potential target for receptor mimicry.

An indirect double-antibody sandwich enzyme-linked immunosorbent assay (ELISA) using baculovirus-expressed antigen for the detection of antibodies to glycoprotein E of pseudorabies virus and comparison of the method with blocking ELISAs

Antibodies in porcine sera against glycoprotein E (gE) of pseudorabies virus (PRV) are usually measured in blocking enzyme-linked immunosorbent assays (ELISAs) with one or two murine monoclonal antibodies (MAbs) directed against gE. Our aim was to develop a confirmation assay which is based on another principle and which is able to detect antibodies directed against most potential binding sites on gE with high specificity. Therefore, we developed an indirect double-antibody sandwich assay (IDAS) using recombinant gE expressed by baculovirus (BacgE960). A fragment of the gE gene consisting of nucleotide positions +60 to +1020 of gE, coding for the major antigenic sites of gE but not the transmembrane region, was cloned behind the signal sequence of PRV gG and the p10 promoter in a baculovirus vector. Immunoblot analysis showed that the expressed protein reacted with MAbs directed against five of the six antigenic sites on gE. Although the conformation of some antigenic sites, notably antigenic sites E and C, was not identical to their natural conformation, the expressed protein bound gE-specific antibodies in porcine sera in Western blots (immunoblots) and ELISAs. For the IDAS, a coating MAb directed against the nonimmunodominant antigenic site A on gE was chosen. A major obstacle in binding ELISAs, such as the IDAS, appeared to be the high nonspecific binding activity observed in porcine sera. As a result, sera could be tested only in relatively high dilutions in the BacgE960 IDAS, in contrast to the testing of sera in blocking ELISAs. The sensitivity and specificity of the newly developed BacgE960 IDAS were evaluated and compared with those of five commercially available blocking ELISAs by using several sets of sera of known PRV disease history. The BacgE960 IDAS assay had a high diagnostic specificity and a moderate sensitivity. The five blocking ELISAs differed remarkably in sensitivity and specificity, thereby illustrating the need for standardization and confirmation. We conclude that the BacgE960 IDAS is a useful and specific additional (confirmatory) test for the detection of antibodies to gE.

Identification of thyroid blocking antibodies and receptor epitopes in autoimmune hypothyroidism by affinity purification using synthetic TSH receptor peptides

To examine the interaction of immunoglobulins from patients with newly diagnosed hypothyroidism with the TSH receptor (TSHr), we tested protein-A purified IgG in an ELISA assay with a series of peptides representing the entire extracellular domain (ECD) of human TSHr. Antibodies bound, on average, 4.1 peptides (range 0-16) per patient, and antibodies from 26 of 30 patients (86.6%) demonstrated binding to at least one peptide. Six of the 20-mer peptides (61, 151, 181, 301, 361, 376) were most frequently recognized. These were used to construct affinity columns and separate IgGs from 10 patients into bound and unbound fractions. All fractions were tested for their ability to stimulate and inhibit cAMP generation in FRTL-5 cells. Inhibitory IgGs were purified from 9 patients (90%), suggesting that the incidence of blocking antibodies (TBAb) in autoimmune hypothyroidism is higher than previously reported. 7 of 10 patients had antibodies that recognized peptide 361 further supporting the importance of this epitope in TBAb binding. Anti-microsomal and anti-thyroglobulin antibodies did not co-purify with inhibitory antibodies, and were always in the unbound fractions. We found no correlation between the pattern of antibody binding or bioactivity with clinical manifestations of hypothyroidism.

CONCLUSIONS

(1) The majority of patients with autoimmune hypothyroidism have antibodies against the TSHr-ECD that recognized linear epitopes. Most have antibodies directed at more than one site and the pattern is quite heterogeneous. (2) Six sites (noted above) are most frequently recognized. (3) Inhibitory antibodies are distinct from anti-microsomal and anti-thyroglobulin antibodies.