Preparation of F(ab')2 fragments from mouse IgG of various subclasses

siRNA Targeting and Treatment of Gastrointestinal Diseases

RNA interference via small interfering RNA (siRNA) offers opportunities to precisely target genes that contribute to gastrointestinal (GI) pathologies, such as inflammatory bowel disease, celiac, and esophageal scarring. Delivering the siRNA to the GI tract proves challenging as the harsh environment of the intestines degrades the siRNA before it can reach its target or blocks its entry into its site of action in the cytoplasm. Additionally, the GI tract is large and disease is often localized to a specific site. This review discusses polymer and lipid‐based delivery systems for protection and targeting of siRNA therapies to the GI tract to treat local disease.

Evidence for intermolecular domain exchange in the Fab domains of dimer and oligomers of an IgG1 monoclonal antibody

Recombinant protein therapeutics have become increasingly useful in combating human diseases, such as cancer and those of genetic origin. One quality concern for protein therapeutics is the content and the structure of the aggregated proteins in the product, due to the potential immunogenicity of these aggregates. Collective efforts have led to a better understanding of some types of protein aggregates, and have revealed the diversity in the structure and cause of protein aggregation. In this work we used a broad range of analytical techniques to characterize the quinary structure (complexes in which each composing unit maintains native quaternary structure) of the stable non-covalent dimer and oligomers of a monoclonal IgG1λ antibody. The results supported a mechanism of intermolecular domain exchange involving the Fab domains of 2 or more IgG molecules. This mechanism can account for the native-like higher order (secondary, tertiary and disulfide bonding) structure, the stability of the non-covalent multimers, and the previously observed partial loss of the antigen-binding sites without changing the antigen-binding affinity and kinetics of the remaining sites (Luo et al., 2009, mAbs 1:491). Furthermore, the previously observed increase in the apparent affinity to various Fcγ receptors (ibid), which may potentially promote immunogenicity, was also explained by the quinary structure proposed here. Several lines of evidence indicated that the formation of multimers by the mechanism of intermolecular domain exchange took place mostly during expression, not in the purified materials. The findings in this work will advance our knowledge of the mechanisms for aggregation in therapeutic monoclonal antibodies.

Fab'-bearing siRNA TNFα-loaded nanoparticles targeted to colonic macrophages offer an effective therapy for experimental colitis

Patients suffering from inflammatory bowel disease (IBD) are currently treated by systemic drugs that can have significant side effects. Thus, it would be highly desirable to target TNFα siRNA (a therapeutic molecule) to the inflamed tissue. Here, we demonstrate that TNFα siRNA can be efficiently loaded into nanoparticles (NPs) made of poly (lactic acid) poly (ethylene glycol) block copolymer (PLA-PEG), and that grafting of the Fab' portion of the F4/80 Ab (Fab'-bearing) onto the NP surface via maleimide/thiol group-mediated covalent bonding improves the macrophage (MP)-targeting kinetics of the NPs to RAW264.7 cells in vitro. Direct binding was shown between MPs and the Fab'-bearing NPs. Next, we orally administered hydrogel (chitosan/alginate)-encapsulated Fab'-bearing TNFα-siRNA-loaded NPs to 3% dextran sodium sulfate (DSS)-treated mice and investigated the therapeutic effect on colitis. In vivo, the release of TNFα-siRNA-loaded NPs into the mouse colon attenuated colitis more efficiently when the NPs were covered with Fab'-bearing, compared to uncovered NPs. All DSS-induced parameters of colonic inflammation (e.g., weight loss, myeloperoxidase activity, and Iκbα accumulation) were more attenuated Fab'-bearing NPs loaded with TNFα siRNA than without the Fab'-bearing. Grafting the Fab'-bearing onto the NPs improved the kinetics of endocytosis as well as the MP-targeting ability, as indicated by flow cytometry. Collectively, our results show that Fab'-bearing PLA-PEG NPs are powerful and efficient nanosized tools for delivering siRNAs into colonic macrophages.

Hydrophilic diol monolith for the preparation of immuno-sorbents at reduced nonspecific interactions

A polar organic polymer monolith (M1) was introduced for performing immunoaffinity chromatography (IAC) at reduced nonspecific interactions. The M1 monolith was prepared by the in situ polymerization of glyceryl methacrylate (GMM) and pentaerythritol triacrylate (PETA). Through its surface diol groups, M1 provided the functionalities to immobilize antibodies. Anti-haptoglobin antibody was used as the model antibody to study the overall behavior of the immuno monolith M1 in terms of its binding to the antigen and to evaluate its nonspecific binding with other proteins, especially the high-abundance human serum proteins. To better assess the suitability of M1 for IAC, other immuno monoliths were prepared and compared with the immuno monolith M1. Two monoliths were of the traditional ones: copolymers of (i) glycidyl methacrylate and ethylene glycol dimethacrylate (EDMA) and (ii) GMM and EDMA, referred to as M2 and M3, respectively. A fourth monolith involving the copolymerization of N-(3-aminopropyl)methacrylamide hydrochloride and EDMA (M4) was introduced to allow the site-directed immobilization of antibodies. Owing to its hydroxyl groups, the M1 exhibited negligible nonspecific hydrophobic interactions with proteins. On the other hand, M4 exhibited extensive electrostatic interactions, while the M2 and to a lesser extent M3 exhibited hydrophobic interactions.

Parkinson disease IgG and C5a-induced synergistic dopaminergic neurotoxicity: Role of microglia

Increasing evidence suggests the involvement of immune/inflammatory system in Parkinson's disease (PD). Many immune/inflammatory factors may synergistically participate in PD. In this study, we demonstrated that immunoglobulin G from the serum of 4/11 PD patients (PDIgG, 60microg/ml) and recombinant human C5a (0.1nM) synergistically induced selective dopaminergic neurodegeneration in rat mesencephalic neuron-glia cultures, while that PDIgG alone or C5a alone was minimally toxic or nontoxic. IgG from 17 disease controls and from 7 normal controls did not significantly induce dopaminergic neurotoxicity in the cultures even in the presence of C5a. Using mesencephalic neuron-enriched cultures, we found that the synergistic dopaminergic neurotoxicity was mediated by glia. The results from microglia-supplemented neuronal cultures, astroglia-supplemented neuronal cultures and neuron-astroglia cocultures indicated that microglia, not astroglia, played a pivotal role in the neurotoxicity. Through immunocytochemistry analysis and assay of proinflammatory factors, we observed that each of the four PDIgGs (60microg/ml) and C5a (0.1nM) synergistically induced microglia activation and production of superoxide and nitric oxide (NO) in neuron-glia cultures. Further investigations indicated that superoxide and NO were both responsible for the synergistic neurotoxicity. Finally, using F(ab')(2) fragments of PDIgG, we demonstrated that microglial Fc receptors may play an important role in the neurotoxicity. Our work provides new evidence for the involvement of the immune/inflammatory system in PD and helpful clues for studying the combined effect of antibody and complement on microglia.

ANCA-induced neutrophil F-actin polymerization: implications for microvascular inflammation

BACKGROUND

The antineutrophil cytoplasmic antibody (ANCA)-positive vasculitides are characterized by a necrotizing vasculitis of small vessels with neutrophil infiltration. The reasons behind the selectivity for small vessels remain unclear, but may relate to the necessity for neutrophils to deform in order to pass through capillaries. The resistance to deformation of neutrophils largely arises from their actin cytoskeleton. It is hypothesized that ANCA, by inducing actin polymerization, increases neutrophil rigidity and contributes to their sequestration in capillaries.

METHODS

To test this hypothesis, neutrophils were treated with IgG-ANCA and the following characterizations: formation of filamentous F-actin (by flow cytometry); changes in morphology (by fluorescence and electron microscopy); and the potential to obstruct microvessels (by measuring entry times into micropipettes with comparable diameters to capillaries). The neutrophil signaling mechanisms activated by IgG-ANCA were investigated using blocking antibodies to Fcgamma receptors and inhibitors of tyrosine phosphorylation. Protein tyrosine phosphorylation was examined by immunoblotting of cell lysates, and calcium fluxes were measured by spectrofluorimetry of Fura-2 pentakis (acetoxymethyl) ester (Fura 2-AM) labeled neutrophils.

RESULTS

IgG-ANCA led to a significant dose-dependent actin polymerization over about 10 minutes. Over the same period, neutrophils became distorted in shape and more resistant to micropipette aspiration. Treatment with normal IgG caused less marked and delayed changes in these parameters. Actin polymerization required engagement of FcgammaRIIa receptor, tyrosine phosphorylation, and calcium fluxes.

CONCLUSION

These novel findings reveal signaling mechanisms that underlie ANCA-induced actin polymerization and might explain the predilection for small vessels in IgG-ANCA-associated vasculitis.

Airway IgG counteracts specific and bystander allergen-triggered pulmonary inflammation by a mechanism dependent on Fc gamma R and IFN-gamma

Besides IgE, the Ab isotype that gives rise to sensitization and allergic asthma, the immune response to common inhalant allergens also includes IgG. Increased serum titers of allergen-specific IgG, induced spontaneously or by allergen vaccination, have been implicated in protection against asthma. To verify the interference of topical IgG with the allergen-triggered eosinophilic airway inflammation that underlies asthma, sensitized mice were treated by intranasal instillation of specific IgG, followed by allergen challenge. This treatment strongly reduced eosinophilic inflammation and goblet cell metaplasia, and increased Th1 reactivity and IFN-gamma levels in bronchoalveolar lavage fluid. In contrast, inflammatory responses were unaffected in IFN-gamma-deficient mice or when applying F(ab')(2). Although dependent on specific allergen-IgG interaction, inflammation triggered by bystander allergens was similarly repressed. Perseverance of inflammation repression, apparent after secondary allergen challenge, and increased allergen capture by alveolar macrophages further characterized the consequences of topical IgG application. These results assign a novel protective function to anti-allergen IgG namely at the local level interference with the inflammatory cascade, resulting in repression of allergic inflammation through an FcgammaR- and IFN-gamma-dependent mechanism. Furthermore, these results provide a basis for topical immunotherapy of asthma by direct delivery of anti-allergen IgG to the airways.

Identification of a putative pathway for the muscle homing of stem cells in a muscular dystrophy model

Attempts to repair muscle damage in Duchenne muscular dystrophy (DMD) by transplanting skeletal myoblasts directly into muscles are faced with the problem of the limited migration of these cells in the muscles. The delivery of myogenic stem cells to the sites of muscle lesions via the systemic circulation is a potential alternative approach to treat this disease. Muscle-derived stem cells (MDSCs) were obtained by a MACS(R) multisort method. Clones of MDSCs, which were Sca-1+/CD34-/L-selectin+, were found to adhere firmly to the endothelium of mdx dystrophic muscles after i.v. or i.m. injections. The subpopulation of Sca-1+/CD34- MDSCs expressing L-selectin was called homing MDSCs (HMDSCs). Treatment of HMDSCs with antibodies against L-selectin prevented adhesion to the muscle endothelium. Importantly, we found that vascular endothelium from striate muscle of young mdx mice expresses mucosal addressin cell adhesion molecule-1 (MAdCAM-1), a ligand for L-selectin. Our results showed for the first time that the expression of the adhesion molecule L-selectin is important for muscle homing of MDSCs. This discovery will aid in the improvement of a potential therapy for muscular dystrophy based on the systemic delivery of MDSCs.

High-performance affinity chromatography for characterization of human immunoglobulin G digestion with papain

Reactive continuous rods of macroporous poly(glycidyl methacrylate-co-ethylene dimethacrylate) were prepared within the confines of a stainless steel column. Then papain was immobilized on these monoliths either directly or linked by a spacer arm. In a further step, a protein A affinity column was used for the characterization of the digestion products of human immunoglobulin G (IgG) by papain. The results showed that papain immobilized on the monolithic rod through a spacer arm exhibits higher activity for the digestion of human IgG than that without a spacer arm. The apparent Michaelis-Menten kinetic constants of free and immobilized papain, K(m) and V(max), were determined. The digestion conditions of human IgG with free and immobilized papain were optimized. Comparison of the thermal stability of free and immobilized papain showed that the immobilized papain exhibited higher thermal stability than the free enzyme. The half-time of immobilized papain reaches about a week under optimum pH and temperature conditions.

Role of Fcgamma receptors in nigral cell injury induced by Parkinson disease immunoglobulin injection into mouse substantia nigra

Immune/inflammatory factors have been implicated in the pathogenesis of Parkinson's disease (PD). Immunoglobulin G (IgG) from patients with PD can induce injury of dopaminergic neurons following stereotaxic injection into rat substantia nigra (SN). The PD IgG can be demonstrated in vitro to activate microglia via the Fcgamma receptor (Fcgamma R) and induce dopaminergic cell injury. To confirm the involvement of microglia and their Fcgamma R in IgG-induced lesions of SN in vivo we analyzed the tyrosine hydroxylase (TH)-positive cell loss in SN par compacta (SNpc) in mice lacking Fcgamma receptors (Fcgamma R(-/-)) and wild type (Fcgamma R(+/+)). At 1 day after stereotaxic injection of PD IgG into the SN of Fcgamma R(+/+) mice there was a 27% increase in the number of CD11b-positive microglial cells and no significant loss of TH-positive cells. At 14 days after the stereotaxic injection, the number of microglial cells was increased by 42%, accompanied by a 40% loss of TH-positive neurons in the SNpc. PD IgG injection in Fcgamma R(-/-) mice resulted in no significant increase of microglia and no loss of TH-positive cells in the SNpc at any time point. The injection of F(ab')(2) fragments of PD IgG was able to induce TH-positive neuronal loss in the SNpc only when the injected animals raised antibodies against the injected human IgG fragments, which confirmed the importance of the Fcgamma R in microglial activation and nigral injury.

Synthesis of bifunctional antibodies for immunoassays

The synthesis of bifunctional antibodies using the principle of solid-phase synthesis is described. Two Fab' fragments were chemically linked together via a bismaleimide crosslinking reagent. The F(ab')(2) fragments from intact immunoglobulin G (IgG) were prepared using an immobilized pepsin column. Goat, mouse, and human antibodies were digested completely within 4 h. The F(ab')(2) fragments thus produced did not contain any IgG impurities. Fab' fragments were produced by reducing the heavy interchain disulfide bonds using 2-mercaptoethylamine. Use of the solid-phase reactor in the preparation of the bifunctional antibodies eliminated many of the time-consuming separation steps between the fragmentation and conjugation steps. This procedure facilitates the automation of bifunctional antibody preparation and the rapid optimization of reaction conditions.

Papain digestion of different mouse IgG subclasses as studied by electrospray mass spectrometry

On-line liquid chromatography-electrospray ionization mass spectrometry (LC/ESI-MS) has been utilized to monitor the papain digestion of mouse monoclonal antibodies (mAb) of different subclasses (IgG1, IgG2a, IgG2b, and IgG3). The method is simple, rapid, sensitive, and allows for simultaneous determination of digestion products and the identification of microheterogenous fragments. The results provide important insight into the mechanism of papain digestion of mouse IgGs of different subclasses.

Evaluation of a high IgE-responder mouse model of allergy to bovine beta-lactoglobulin (BLG): development of sandwich immunoassays for total and allergen-specific IgE, IgG1 and IgG2a in BLG-sensitized mice

An animal model of food allergy represents an important tool for studying the mechanisms of induction and repression of an allergic reaction, as well as for the development of an immunotherapy to prevent or minimize such an adverse reaction. IgE and IgG1 (Th2 response) vs. IgG2a (Th1 response) are good markers for the induction of an allergic response in mice. Nevertheless, while the total serum concentrations of these isotypes are easy to measure using classical sandwich immunoassays, this is not the case for allergen-specific isotypes. To develop an animal model of allergy to bovine beta-lactoglobulin (BLG), we set up quantitative assays for total and for allergen-specific IgE, IgG1 and IgG2a. Microtiter plates coated either with anti-isotype antibodies (Abs) or with allergen were used for Ab capture, while anti-isotype Fab' fragments coupled to acetylcholinesterase were used for visualization. These assays of anti-BLG specific Abs are original in two ways. First, assay calibration is performed using anti-BLG specific mAbs, thus allowing good quantification of the different isotypes and subclasses of serum antibodies. Second, the detection of all anti-BLG specific Abs, i.e., those recognizing both the native and denatured forms of the protein, is achieved through indirect coating of BLG using biotin-streptavidin binding. The present assays are quantitative, specific to the isotype (cross-reactivity <0.5%), very sensitive (detection limit in the 10 pg/ml range), and reproducible (coefficient of variation less than 10%). Applied to the humoral response in mice sensitized with BLG adsorbed on alum, these assays proved to be a very useful tool for monitoring high IgE-responder mice following BLG immunization, and for an immunotherapy directed at polarizing the immune response.

Bivalency and epitope specificity of a high-affinity IgG3 monoclonal antibody to the Streptococcus group A carbohydrate antigen. Molecular modeling of a Fv fragment

The binding of Strep 9, a mouse monoclonal antibody (mAb) of the IgG3 subclass directed against the cell-wall polysaccharide of Group A Streptococcus (GAS), has been characterized. The intact antibody and proteolytic fragments of Strep 9 bind differently to GAS: the intact mAb and F(ab)2' have greater affinity for the carbohydrate epitope than the monomeric Fab or F(ab)'. A mode of binding in which Strep 9 binds bivalently to portions of the polysaccharide on adjacent chains on GAS is proposed. A competitive ELISA protocol using a panel of carbohydrate inhibitors shows that the branched trisaccharide, beta-D-GlcpNAc-(1-->3)-[alpha-L-Rhap-(1-->2)]-alpha-L-Rhap, and an extended surface are key components of the epitope recognized by Strep 9. Microcalorimetry measurements with the mAb and two synthetic haptens, a tetrasaccharide and a hexasaccharide, show enthalpy-entropy compensation as seen in other oligosaccharide-protein interactions. Molecular modeling of the antibody variable region by homology modeling techniques indicates a groove-shaped combining site that can readily accommodate extended surfaces. Visual docking of an oligosaccharide corresponding to the cell-wall polysaccharide into the site provides a putative model for the complex, in which a heptasaccharide unit occupies the site and the GlcpNAc residues of two adjacent branched trisaccharide units occupy binding pockets within the groove-shaped binding site.

Processing of antibodies to the MHC class II antigen by B-cell lymphomas: release of Fab-like fragments into the medium

Lym-1, an anti-MHC class II Ab, displayed a unique processing pathway after binding to the surface of Raji B-lymphoma cells, in which Fab-like fragments were gradually released into the medium. The fragments had reduced interchain disulfide bonds. Fragmentation was markedly reduced by inhibitors of intracellular catabolism, namely ammonium chloride, chloroquine and leupeptin. The capacity of the process was high, and fragmentation of approximately 5x10(6) Ab molecules per cell per day was measured directly, in what can be considered to be a minimum estimate. Five other Abs to the MHC class II antigen were tested similarly on Raji and on three other B-cell lymphomas: none showed the same high level of fragmentation seen with Lym-1 binding to Raji, but significant fragmentation did occur with some of the Abs, particularly EDU-1 and L243. The level of fragmentation depended on the cell line as well as on the particular Ab. The other 5 Abs were all catabolized, to low molecular weight material, much more extensively than Lym-1. Part of the difference between Abs can probably be attributed to the fortuitous, preferential labeling of Lym-1 on the light chain, since the data suggest that the Fc fragment is fully degraded while the Fab-like fragment is released into the supernatant. This pathway of Ab processing is likely to be related to the physiology of the MHC class II antigen, which recycles into a mildly proteolytic intracellular compartment.

Identification of a novel surface molecule, RM3/1, that contributes to the adhesion of glucocorticoid-induced human monocytes to endothelial cells

The functions of different populations of peripheral blood monocytes in the course of an inflammatory reaction are presently not fully understood. In particular, the mechanisms for their specific recruitment to an inflammatory site are not yet known. We investigated a dexamethasone (Dex)-inducible monocyte subtype and its adhesion to either unstimulated or lipopolysaccharide (LPS)- or interferon (IFN)-gamma-stimulated human umbilical vein endothelial cells (HUVEC). The Dex-induced monocytes were characterized by the expression of the surface glycoprotein RM3/1. It was found that pretreatment of monocytes with Dex increased their adhesion to unstimulated and stimulated HUVEC. This increase in adhesion was paralleled by the expression of the RM3/1 surface molecule. Treatment with cyclosporin A (CsA) caused a down-regulation of the RM3/1 density per cell by 67% and also decreased adhesion to HUVEC. In contrast, the expression of other adhesion molecules remained unaffected by Dex or CsA treatment. Treatment of Dex-induced monocytes with antibodies against RM3/1, CD11a, CD11b, CD11c, CD14 and CD18 resulted in suppression of adhesion to stimulated HUVEC by 46%, 18%, 17%, 12%, 25% and 15%, respectively. Antibodies to the known adhesion molecules on endothelial cells (vascular cell adhesion molecule-1, E-selectin) did not block adhesion of Dex-induced monocytes. However, the combination of antibodies to RM3/1 and CD14 inhibited adhesion to LPS-stimulated HUVEC by 74%. These effects were also seen on IFN-gamma-stimulated HUVEC, where adhesion of Dex-induced monocytes was blocked with antibodies to RM3/1 + CD14 by 63%. From this, it is concluded that the RM3/1-molecule is a novel surface molecule that contributes to the adhesion of cortisone-induced monocytes to LPS or cytokine-stimulated endothelial cells.

Solid phase synthesis of bifunctional antibodies

Bifunctional antibodies were prepared using the principle of solid-phase synthesis. The two Fab' fragments were chemically linked together via a bismaleimide crosslinking reagent. The F(ab')2 fragments from intact IgG were prepared using an immobilized pepsin column. Goat, mouse and human antibodies were digested completely within 4 h. The F(ab')2 fragments thus produced did not contain any IgG impurities. The Fab' fragments were produced by reducing the inter-heavy chain disulfide bonds using 2-mercaptoethylamine. The use of the solid-phase reactor in the preparation of the bifunctional antibodies eliminated many of the time-consuming separation steps between the fragmentation and conjugation steps. This procedure facilitates the automation of the bifunctional antibody preparation and the rapid optimization of reaction conditions.

A novel strategy affords high-yield coupling of antibody Fab' fragments to liposomes

A new assay for the production of reactive sulfhydryl-bearing antibody Fab' fragments has been utilized to develop conditions affording high efficiencies of coupling of mouse and rabbit IgG-derived Fab' fragments to lipid vesicles containing maleimidyl-functionalized phospholipids. Cysteine and mercaptoethylamine, but not dithiothreitol, reduce antibody F(ab')2 to Fab' fragments in very good yields under conditions where overreduction to heavy and light chains is minimized. Surprisingly, however, a large fraction of the Fab' fragments generated under these conditions can lack maleimide-reactive sulfhydryl groups, as demonstrated using a maleimidyl-poly(ethylene glycol) conjugate to shift selectively the electrophoretic mobility of the reactive sulfhydryl-bearing Fab' fragments. After modification of F(ab')2 reduction conditions specifically to maximize the yield of the latter fraction, it is possible to achieve high and very reproducible coupling of functional Fab' fragments to liposomes (equivalent to coupling of ca. 70% of total input protein and almost 100% of the reactive sulfhydryl-bearing Fab' fraction). A novel phospholipid-poly(ethylene glycol)-maleimide 'anchor' allows particularly efficient coupling of Fab' fragments to liposomes, even using relatively low liposome concentrations and molar percentages of the liposome-incorporated 'anchor' species. These results demonstrate that with appropriate optimization of the conditions for Fab' production and liposome coupling, Fab' fragments can be coupled to liposomes with efficiencies comparable to or exceeding those reported for coupling of intact antibodies. These results should facilitate the wider use of Fab' fragments as a potentially advantageous alternative to intact antibodies for liposomal targeting in various applications.

Anti-endotoxin monoclonal antibodies inhibit secretion of tumor necrosis factor-alpha by two distinct mechanisms

OBJECTIVE

To determine whether monoclonal antibodies (mAbs) directed against lipopolysaccharide (LPS, endotoxin) act by promoting LPS neutralization, LPS uptake by macrophages, or both processes, the authors assessed the effects of these agents on LPS-induced cytokine secretion and cellular uptake of LPS.

SUMMARY BACKGROUND DATA

MAbs directed against LPS have been shown to attenuate LPS-induced macrophage tumor necrosis factor-alpha (TNF-alpha) secretion, a process that may contribute to protective capacity. The mechanisms by which this process occurs have not been established.

METHODS

MAbs directed against LPS were evaluated in vitro for their capacity to (1) inhibit TNF-alpha secretion, and (2) alter fluorescein isothiocyanate-labeled LPS uptake (employing flow cytometry analysis and fluorescence microscopy) by the macrophage-like cell line RAW 264.7.

RESULTS

MAb 8G9, an IgG3 directed against the O-antigen polysaccharide region of Escherichia coli 0111:B4 LPS, significantly reduced LPS-induced TNF-alpha secretion and promoted a more than 40-fold increase in LPS uptake by macrophages. The authors established that this was mediated by a Fc receptor-mediated process because 8G9 F(ab')2 fragments that lack the Fc portion of the IgG molecule were capable of inhibiting TNF-alpha secretion, but did not promote increased LPS uptake to the same degree. Cross-reactive, anti-deep core/lipid A mAb 1B6, an IgG2a, also promoted uptake of E. coli 0111:B4 LPS and O-antigen polysaccharide-deficient E. coli J5 LPS, but only inhibited TNF-alpha secretion induced by E. coli J5 LPS to which it binds most efficiently. MAb 3D10, an IgM also directed against the O-antigen polysaccharide region of E. coli 0111:B4 LPS, inhibited TNF-alpha secretion but did not increase cellular uptake of LPS, presumably acting solely due to LPS neutralization. Polymyxin B, an antibiotic that binds stoichiometrically to the lipid A portion of LPS, inhibited TNF-alpha secretion and prevented cellular LPS uptake.

CONCLUSIONS

These results suggest that IgG and IgM anti-LPS mAbs exert protective capacity by extracellular neutralization of LPS, while IgG Fc receptor-mediated cellular uptake also may serve to bypass macrophage activation and TNF-alpha secretion by promoting internalization and intracellular neutralization.

Leukocyte accumulation promoting fibrin deposition is mediated in vivo by P-selectin on adherent platelets

The glycoprotein P-selectin is a cell adhesion molecule of stimulated platelets and endothelial cells, which mediates the interaction of these cells with neutrophils and monocytes. It is a membrane component of cell storage granules, and is a member of the selectin family which includes E-selectin and L-selectin. P-selectin recognizes both lineage-specific carbohydrate ligands on monocytes and neutrophils, including the Lewis x antigen, sialic acid, and a protein component. In inflammation and thrombosis, P-selectin may mediate the interaction of leukocytes with platelets bound in the region of tissue injury and with stimulated endothelium. To evaluate the role of P-selectin in platelet-leukocyte adhesion in vivo, the accumulation of leukocytes within an experimental thrombus was explored in an arteriovenous shunt model in baboons. A Dacron graft implanted within an arteriovenous shunt is thrombogenic, accumulating platelets and fibrin within its lumen. These bound platelets express P-selectin. Here we show that antibody inhibition of leukocyte binding to P-selectin expressed on platelets immobilized on the graft blocks leukocyte accumulation and inhibits the deposition of fibrin within the thrombus. These results indicate that P-selectin is an important adhesion molecule on platelets, mediating platelet-leukocyte binding in vivo, that the presence of leukocytes in thrombi is mediated by P-selectin, and that these leukocytes promote fibrin deposition.

Production of functionally active murine and murine::human chimeric F(ab')2 fragments in COS-1 cells

We report here the synthesis, in nonlymphoid cells, of two functionally active recombinant F(ab')2 fragments directed against the tumor marker, human placental alkaline phosphatase (hPLAP). The truncated heavy chain (HC) sequences, E6Hf2 and E6Hy3f2, of the murine F(ab')2 fragment, E6F2, and of the murine::human chimeric F(ab')2 fragment, E6(Hy3,kappa)F2, respectively, were engineered by introducing an in-phase stop codon within the second constant domain of the corresponding parental HC sequence. The antibody-encoding genes were placed under control of the simian virus 40 late promoter and each HC sequence, together with the light chain (LC) sequence, was transiently expressed in COS-1 cells. The truncated HCs were correctly synthesized, processed and assembled with the murine LC and subsequently secreted into the culture medium as functionally active entities with stable hinge region interactions. These results indicate that, under the conditions used, the hinge region was sufficient for the formation of divalent molecules. However, Western blotting revealed the presence of hPLAP-binding half-molecules of E6F2, which was not the case for E6(Hy3,kappa)F2. Since E6F2 and E6(Hy3,kappa)F2 mainly differ by the length of their hinge region (22 and 62 aa residues, respectively) and the number of inter-HC disulfide bridges (four and eleven, respectively), it may be concluded that F(ab')2 fragments with an extended hinge region and several inter-HC disulfide bridges are formed more efficiently.

Single-step purification of F(ab')2 fragments of mouse monoclonal antibodies (immunoglobulins G1) by hydrophobic interaction high performance liquid chromatography using TSKgel Phenyl-5PW

Hydrophobic interaction high performance liquid chromatography (HPLC) using TSKgel Phenyl-5PW was applicable to single-step purification of F(ab')2 fragments from pepsin digests of mouse monoclonal antibodies of IgG1 class. The digests were applied to the gel equilibrated with phosphate-buffered saline containing 1 M ammonium sulfate. F(ab')2 fragments were adsorbed onto the gel using the same buffer, and eluted by reducing the ammonium sulfate concentration to 0 M. The fraction containing F(ab')2 fragments was homogeneous (purity: higher than 98%) by both sodium dodecyl sulfate-polyacrylamide gel electrophoresis and gel filtration HPLC. The recovery of the antigen binding site was 42-58%. The cycle time of the Phenyl-5PW HPLC was 45 min, and F(ab')2 of up to 2200 mg was purified in a cycle. This method could be useful especially for large scale purification of F(ab')2 fragments.

High Level Escherichia coli Expression and Production of a Bivalent Humanized Antibody Fragment

Many clinical uses of antibodies will require large quantities of fragments which are bivalent and humanized. We therefore attempted to generate humanized F(ab')2 fragments by secretion from E. coli. Titers of 1-2 g l-1 of soluble and functional Fab' fragments have been routinely achieved as judged by antigen-binding ELISA. Surprisingly, this high expression level of Fab' in the periplasmic space of E. coli does not drive dimerization. However, we have developed a protocol to directly and efficiently recover Fab' with the single hinge cysteine in the free thiol state, allowing F(ab')2 formation by chemically-directed coupling in vitro. The E. coli derived humanized F(ab')2 fragment is indistinguishable from F(ab')2 derived from limited proteolysis of intact antibody in its binding affinity for the antigen, p185HER2, and anti-proliferative activity against the human breast tumor cell line, SK-BR-3, which over-expresses p185HER2. This system makes E. coli expression of bivalent antibody fragments for human therapy (or other uses) practical.

Anti-idiotypic antibody probes of neuronal nicotinic receptors

Monoclonal anti-idiotypic antibodies specific for the combining site on a monoclonal antinicotine were used in immunocytochemistry to localize nicotine binding sites on rat brain cortical sections and in immunoaffinity chromatography to isolate receptor from solubilized brain tissue. The receptor, which consists of two subunits with Mr values of 43 and 50 kDa, was eluted from the antiidiotype column with either pH3 citrate buffer or 25 mM (-)-nicotine, but was not present in eluates from immobilized anti-Electrophorus acetylcholine receptor or anti-methotrexate. The anti-idiotypes specifically inhibited [3H]nicotine binding to rat brain homogenate and (-)-nicotine inhibited anti-idiotype binding to brain sections based on abrogation of immunofluorescence staining. These results are consistent with the operational definition of the anti-idiotypes as the internal image of nicotine, and demonstrate their value as immunochemical probes of nicotinic receptors.

Monoclonal antibodies to the insulin receptor mimic metabolic effects of insulin but do not stimulate receptor autophosphorylation in transfected NIH 3T3 fibroblasts

The metabolic actions of insulin and anti-insulin receptor monoclonal antibodies were compared with their effects on insulin receptor phosphorylation in mouse NIH 3T3 fibroblasts transfected with human insulin receptor cDNA. In serum-starved NIH 3T3 HIR3.5 cells, uptake of 2-deoxy-[3H]glucose was stimulated up to 2-fold after 30 min with insulin, with a half-maximal effect at 0.1 nM insulin. Incorporation of [3H]thymidine was stimulated approximately 12-fold after a 16-hr preincubation with insulin, with a half-maximal effect at 2 nM insulin. Phosphorylation of insulin receptor beta-subunit in cells prelabeled with [32P]phosphate was increased 10- to 20-fold within 5 min of adding insulin, with a half-maximal effect at approximately 3 nM insulin. Monoclonal antibodies reacting with four different epitopes on the insulin receptor mimicked the effect of insulin on 2-deoxyglucose uptake. These antibodies also stimulated thymidine incorporation, although the maximum stimulation was only approximately 30% that of insulin. Two antibodies (25-49 and 83-14) showed a similar concentration dependence to insulin in their metabolic effects and in the inhibition of 125I-labeled insulin binding to cells. The other two antibodies (83-7 and 18-44) were somewhat less potent and did not inhibit insulin binding. None of the antibodies significantly increased insulin receptor phosphorylation at concentrations up to 100 nM, which at least in the case of 25-49 and 83-14 was sufficient for full receptor occupancy. It is concluded that the insulin-like metabolic effects of antibodies involve a mechanism of receptor activation that is independent of autophosphorylation and hence that receptor autophosphorylation is not an essential step in triggering at least some events in the insulin signaling pathway.