Immunology of carbohydrate-based vaccines

Carbohydrates are considered as promising targets for vaccine development against infectious diseases where cell surface glycan's on many infectious agents are attributed to playing an important role in pathogenesis. Understanding the relationship between carbohydrates and immune components at a molecular level is crucial for the development of well-defined vaccines. Recently, carbohydrate immunology research has been accelerated by the development of new technologies that contribute to the design of optimum antigens, synthesis of antigens and the studies of antigen-antibody interactions, and as a result, several promising carbohydrate-based vaccine candidates have been prepared in recent years. This article briefly presents the mechanistic pathways of polysaccharide, glycoconjugate, glycolipid and zwitterionic vaccines and the interplay between carbohydrate antigen and immune response.

Maximum-Entropy Models of Sequenced Immune Repertoires Predict Antigen-Antibody Affinity

The immune system has developed a number of distinct complex mechanisms to shape and control the antibody repertoire. One of these mechanisms, the affinity maturation process, works in an evolutionary-like fashion: after binding to a foreign molecule, the antibody-producing B-cells exhibit a high-frequency mutation rate in the genome region that codes for the antibody active site. Eventually, cells that produce antibodies with higher affinity for their cognate antigen are selected and clonally expanded. Here, we propose a new statistical approach based on maximum entropy modeling in which a scoring function related to the binding affinity of antibodies against a specific antigen is inferred from a sample of sequences of the immune repertoire of an individual. We use our inference strategy to infer a statistical model on a data set obtained by sequencing a fairly large portion of the immune repertoire of an HIV-1 infected patient. The Pearson correlation coefficient between our scoring function and the IC50 neutralization titer measured on 30 different antibodies of known sequence is as high as 0.77 (p-value 10-6), outperforming other sequence- and structure-based models.

Tissue factor in antiphospholipid antibody-induced pregnancy loss: a pro-inflammatory molecule

Fetal loss in patients with antiphospholipid antibodies (aPL) has been ascribed to thrombosis of placental vessels. However, we have shown that inflammation, specifically complement activation with generation of the anaphylotoxin C5a, is an essential mediator of fetal injury. We have analysed the role of tissue factor (TF) in a mouse model of aPL-induced pregnancy loss. TF is the major cellular activator of the coagulation cascade but also has cell signaling activity. Mice that received aPL-IgG showed strong TF staining throughout the decidua and on embryonic debris. This TF staining was not associated with either fibrin staining or thrombi in deciduas. The absence of fibrin deposition and thrombi suggests that TF-dependent activation of coagulation does not mediate aPL-induced pregnancy loss.We found that either blockade of TF with a monoclonal antibody in wild type mice or a genetic reduction of TF prevented aPL-induced inflammation and pregnancy loss indicated a pathogenic role for TF in aPL-induced pregnancy complications. In response to aPL-generated C5a, neutrophils express TF potentiating inflammation in the deciduas and leading to miscarriages. Importantly, we showed that TF in myeloid cells, but not fetal-derived cells (trophoblasts), was associated with fetal injury, suggesting that the site for pathologic TF expression is neutrophils. We found that TF expression in neutrophils contributes to respiratory burst and subsequent trophoblast injury and pregnancy loss induced by aPL. The identification of TF, acting as an important pro-inflammatory mediator in aPL-induced fetal injury, provides a new target for therapy to prevent pregnancy loss in the aPL syndrome.

The conservative physiology of the immune system. A non-metaphoric approach to immunological activity

Historically, immunology emerged as a biomedical science, concerned with host defense and production of anti-infectious vaccines. In the late 50s, selective theories were proposed and from then on, immunology has been based in a close association with the neo-Darwinian principles, such as random generation of variants (lymphocyte clones), selection by extrinsic factors (antigens)—and, more generally, on genetic determinism and functionalism. This association has had major consequences: (1) immunological jargon is full of “cognitive” metaphors, founded in the idea of “foreignness”; (2) the immune system is described with a random clonal origin, coupled to selection by random encounters; and (3) physiological events are virtually absent from immunological descriptions. In the present manuscript, we apply systemic notions to bring forth an explanation including systemic mechanisms able to generate immunological phenomena. We replace “randomness plus selection” and the notion of foreignness by a history of structural changes which are determined by the coherences of the system internal architecture at any given moment. The importance of this systemic way of seeing is that it explicitly attends to the organization that defines the immune system, within which it is possible to describe the conservative physiology of the immune system. Understanding immune physiology in a systemic way of seeing also suggests mechanisms underlying the origin of immunopathogeny and therefore suggests new insights to therapeutic approaches. However, if seriously acknowledged, this systemic/historic approach to immunology goes along with a global conceptual change which modifies virtually everything in the domain of biology, as suggested by Maturana.

Mesangial autoantigens in IgA nephropathy: matrix synthesis and localization

Primary IgA nephropathy, a chronic nephritis with variable prognosis, is characterized by mesangial immunoglobulin A, frequently with codeposition of other immunoglobulin isotypes and complement components accompanying matrix expansion typically preceding glomerular scarring. Glomerular immunoglobulin G, when present, is localized to the mesangial periphery found variably in repeat biopsies. IgG anti-mesangial cell autoantibodies (IgG-MESCA) in sera of patients with IgA nephropathy, specific by F(ab')(2) binding to 48- and 55-kD autoantigen(s) could account for these deposits, but their in vivo localization, and the functional role in promoting scarring is unknown. A specific monoclonal antibody raised previously to these human mesangial cell autoantigen fractions, in this study localized to similar glomerular sites, reinforcing the view that immunoglobulin G deposition in vivo is a result of antibody-autoantigen binding. The propensity for immunoglobulin G more than other isotypes to enhance inflammation prompted study of its functional role in vitro. Using cultured human mesangial cells in a complement-free tritiated glycosaminoglycan synthesis single outcome assay, purified IgG fractions from patient sera increased matrix production in a dose-dependent manner compared with controls. At a constant total IgG concentration, matrix synthesis was proportional to the titre of IgG-MESCA. Autoreactive IgG stimulated matrix synthesis when compared with controls or IgA fractions. These findings are consistent with IgG-MESCA autoantibodies enhancing mesangial matrix synthesis in vitro, which suggests that in IgA nephropathy, similar prosclerotic autoimmune mechanisms might operate. Recombinant TGFbeta(1) also induced matrix synthesis, raising the possibility that both autoimmune mechanisms and those TGFbeta(1)-dependent are functional or inter-related. The pathogenesis of glomerular scarring and loss in IgA nephropathy may include, in part, these mechanisms.

Ferrous Ions and Reactive Oxygen Species Increase Antigen-binding and Anti-inflammatory Activities of Immunoglobulin G

Polyspecific antibodies represent a first line of defense against infection and regulate inflammation, properties hypothesized to rely on their ability to interact with multiple antigens. We demonstrated that IgG exposure to pro-oxidative ferrous ions or to reactive oxygen species enhances paratope flexibility and hydrophobicity, leading to expansion of the spectrum of recognized antigens, regulation of cell proliferation, and protection in experimental sepsis. We propose that ferrous ions, released from transferrin and ferritin at sites of inflammation, synergize with reactive oxygen species to modify the immunoglobulins present in the surrounding microenvironment, thus quenching pro-inflammatory signals, while facilitating neutralization of pathogens.

A new concept of accommodation in ABO-incompatible kidney transplantation

This work focuses on the mechanism of acute antibody-mediated rejection leading to graft loss and the mechanisms of accommodation permitting graft survival in ABO-incompatible kidney transplantation. As previously noted, accommodation occurs only with (i) post-transplant suppression of glycosyltransferase, a product of ABO histo-blood group genes in the graft and (ii) prevention of antigen-antibody reactions and delayed hyperacute rejection due to reduced antigenicity of enzyme-regulated histo-blood group antigens. This article discusses the mechanism of ABO histo-blood group glycosyltransferase suppression. Accommodation is always established in successful ABO-incompatible organ grafts and ABO-minor mismatch bone marrow transplantation. In the former, accommodation develops even though ABO histo-blood types of the recipient and the donor are incompatible. In the latter, infusion of donor-derived bone marrow causes the recipient's blood to be eventually replaced by blood of the donor's type. However, the recipient's organs retain their original tissue type. In successful bone marrow engraftment, accommodation is established regardless of ABO-incompatibility. In organ transplantation the recipient's ABO histo-blood type regulates the graft's ABO histo-blood type, while in bone marrow transplantation the new ABO histo-blood type from the donor suppresses and regulates the ABO histo-blood type in recipient organs. In other words, bone marrow-derived histo-blood type regulates the histo-blood type of the organs.

Development, characterisation and epitope mapping of novel monoclonal antibodies for DJ-1 (PARK7) protein

Mutations in DJ-1 (PARK7) were recently identified as the cause for an autosomal recessive early onset form of familial Parkinson's disease, however, the function of the protein in the brain is yet to be elucidated. Here we report on the development, characterisation and epitope mapping, of two novel monoclonal antibodies to DJ-1. One of them (DJ-1 "clone16") has its epitope between amino acids 56-78 of the human DJ-1 protein and has very similar properties to a commercially available DJ-1 antibody clone 3E8. The second antibody recognised both the rat and human DJ-1 (DJ-1 "clone 48") and its epitope is between amino acids 26-56. We have used immunohistochemistry with these two antibodies to compare the distribution of DJ-1 in human and rat brain tissue. Both antibodies gave similar patterns of labelling in human brain with marked astrocytic expression. Neuronal labelling was weak or absent and the antibodies did not label Lewy bodies or Lewy neurites. In the rat brain, DJ-1 was ubiquitously expressed in neurones but exhibited low expression in astrocytes. These antibodies could be exploited as important tools in dissecting out DJ-1 expression in different species and examination of the role of DJ-1 in Parkinson's disease.

Transfusion-Related Acute Lung Injury and the ICU

Transfusion-related acute lung injury (TRALI) has been the leading cause of transfusion-related deaths reported to the United States Food and Drug Administration for three consecutive years. Although traditionally TRALI has been viewed as having a one event pathogenesis (passive donor anti-leukocyte antibody interacting with a cognate antigen on the recipients leukocytes), emerging evidence suggests that TRALI is a multifactorial syndrome, and a true two-event subtype of ALI. Both recipient predisposition and biological response modifiers, generated during storage of cellular blood products, appear to play major pathogenetic roles. This review highlights recent advances in our knowledge of the pathophysiology of TRALI and recent progress towards a consensus definition of TRALI. It also guides the reader as to the recognition, investigation, and clinical management of TRALI.

[Normobaric hypoxia effects on some parameters of cellular immunity of persons with different blood groups]

We investigated influence of the normobaric hypoxia on separate parameters of cellular immunity of persons with different groups of blood (system ABO). It was established presence of varied direction of immunity changes, which expressiveness depend on the certain antigens (system ABO) The most sensible to hypoxia immunostimulation was immune system of persons with II group of blood, the lowest- with the IV group.

Comparison of antibody--antigen interactions on collagen measured by conventional immunological techniques and atomic force microscopy

We have developed a means of using atomic force microscopy (AFM) to repeatedly localize a small area of interest (4 x 4 microm(2)) within a 0.5-cm(2) area on a heterogeneous sample, to obtain and localize high-resolution images and force measurements on nonideal samples (i.e., samples that better reflect actual biological systems, not prepared on atomically flat surfaces). We demonstrate the repeated localization and measurement of unbinding forces associated with antibody--antigen (ab--ag) interactions, by applying AFM in air and in liquid to visualize and measure polyclonal ab--ag interactions, using chicken collagen as a model system. We demonstrate that molecular interactions, in the form of ab--ag complexes, can be visualized by AFM when secondary antibodies are conjugated to 20-nm colloidal gold particles. We then compare those results with established immunological techniques, to demonstrate broader application of AFM technology to other systems. Data from AFM studies are compared with results obtained using immunological methods traditionally employed to investigate ab--ag interactions, including enzyme-linked immunosorbent assay, immunoblotting, and in situ immunofluorescence. Finally, using functionalized AFM tips with a flexible tether [poly(ethylene glycol) 800] to which a derivatized antibody was attached, we analyzed force curve data to measure the unbinding force of collagen antibody from its antigen, obtaining a value of approximately 90 +/- 40 pN with a MatLab code written to automate the analyses of force curves obtained in force--volume mode. The methodology we developed for embedded collagen sections can be readily applied to the investigation of other receptor--ligand interactions.

Deciphering antibody properties that lead to potent botulinum neurotoxin neutralization

Monoclonal antibodies (mAbs) have been developed that bind to the toxin binding domain (H(C)) of botulinum toxin type A. These mAbs recognize with high affinity nonoverlapping epitopes on native toxin. The potency of a combination of three of the mAbs is almost 100 times greater than that reported for human polyclonal botulinum immune globulin. Potency appears to result largely from a marked increase in binding affinity for toxin that results when antibodies are combined. Precise epitope, or even domain recognized, seems to be of much less importance. The very high affinity required for toxin neutralization suggests why single mAbs that potently neutralize toxin have not been reported. Such affinities are not typically generated by the immune response.

Antibody binding in altered gravity: implications for immunosorbent assay during space flight

A single antibody-incubation step of an indirect, enzyme-linked immunosorbent assay (ELISA) was performed during microgravity, Martian gravity (0.38 G) and hypergravity (1.8 G) phases of parabolic flight, onboard the NASA KC-135 aircraft. Antibody-antigen binding occurred within 15 seconds; the level of binding did not differ between microgravity, Martian gravity and 1 G (Earth's gravity) conditions. During hypergravity and 1 G, antibody binding was directly proportional to the fluid volume (per microtiter well) used for incubation; this pattern was not observed during microgravity. These effects in microgravity may be due to "fluid spread" within the chamber (observed during microgravity with digital photography), leading to greater fluid-surface contact and subsequently antibody-antigen contact. In summary, these results demonstrate that: i) ELISA antibody-incubation and washing steps can be successfully performed by human operators during microgravity, Martian gravity and hypergravity; ii) there is no significant difference in antibody binding between microgravity, Martian gravity and 1 G conditions; and iii) a smaller fluid volume/well (and therefore less antibody) was required for a given level of binding during microgravity. These conclusions indicate that reduced gravity would not present a barrier to successful operation of immunosorbent assays during spaceflight.

Kinetic analysis of interactions between bispecific monoclonal antibodies and immobilized antigens using a resonant mirror biosensor

A resonant mirror biosensor (IAsys) protocol is described for the comparative kinetic analysis of the ability of monoclonal antibodies (Mabs) and bispecific antibodies (Babs) to bind immobilized antigens. The protocol has been optimized and validated using the panel of affinity-purified antibodies, including two parental Mabs, one specific to human immunoglobulin G (hIgG) and another specific to horseradish peroxidase (HRP), and a Bab derived thereof by cell fusion (anti-hIgG/HRP Bab). The real-time kinetic analysis of antigen-antibody interactions using this protocol allows to demonstrate the differences in the avidity of bivalently binding Mabs and monovalent Babs. As shown in our previous study [J. Immunol. Methods 261 (2002) 103], the observed equilibrium association constants (Kass) determined by IAsys using this protocol yield figures almost overlapping with those obtained by solid-phase radioimmunoassay (RIA). The described protocol is suited for the investigation of the effects of valency on the binding properties of antibodies. It also may be applied for the selection of Mabs and Babs with desired features, for different fields of application.

Complement-mediated enhancement of HIV-1 neutralisation by anti-HLA antibodies derived from polytransfused patients

We have recently shown that 'alloimmune sera' derived from polytransfused patients (PTP sera) are able to recognise and neutralise HIV in vitro. In this study we try to identify the protein(s), which are recognised by the PTP sera and elucidate mechanisms responsible for the neutralising capacity of these sera. The PTP sera allowed immunoprecipitation (IP) of HLA class II molecules on HIV-infected cells. To detect a potential cross-reactivity of alloreactive antibodies (Ab) with the HIV envelope protein gp160 or its subunits gp120/gp41 and HLA proteins, ELISA and FACS analyses were performed. The lack of reactivity of the PTP sera against rsgp160 in ELISA or FACS analysis indicated that recognition of cells was independent of HIV infection. To clarify whether interaction of the PTP sera with target cells has any effect on the infection process, virus neutralisation assays were performed. Inhibition of HIV infection was observed only when virus was pre-incubated with the PTP sera. Complement enhanced neutralisation of HIV-1 significantly. This enhancement was not due to complement-mediated lysis, because pre-incubation of the target cells with PTP sera did not inhibit HIV replication. Therefore, the neutralising effect of the Ab was due to blocking of the viral attachment/fusion process and not to negative signalling after infection. Since steric hindrance is possible only when HLA and gp120/gp41 are in close vicinity, isolation of rafts and IP assays were performed. These experiments revealed that gp120 and MHC class II molecules are indeed co-localised. The close physical association of gp120/gp41 and HLA strongly supports a mechanism for neutralisation of HIV by anti-HLA-Ab based on steric hindrance.

Thermodynamic and kinetic aspects of antibody evolution during the immune response to hapten

We determined thermodynamic and kinetic parameters for the antigen-antibody interaction using a group of anti-(4-hydroxy-3-nitrophenyl)acetyl monoclonal antibodies whose differences in amino acid sequences had arisen only from somatic hypermutation. These monoclonal antibodies were considered to have originated from a common ancestor clone and to represent progression along the affinity maturation pathway. The kinetic measurements showed that both association and dissociation rate constants of the antigen-antibody interaction decreased during maturation. Thermodynamic measurements revealed that an increase in affinity was obtained by an increase in entropy without any significant change in enthalpy. These results suggested that the mechanism for the antigen-antibody interaction shifted from a "zipper" type to a "lock-and-key" type during antibody evolution.

The conservative physiology of the immune system

Current immunological opinion disdains the necessity to define global interconnections between lymphocytes and regards natural autoantibodies and autoreactive T cells as intrinsically pathogenic. Immunological theories address the recognition of foreignness by independent clones of lymphocytes, not the relations among lymphocytes or between lymphocytes and the organism. However, although extremely variable in cellular/molecular composition, the immune system preserves as invariant a set of essential relations among its components and constantly enacts contacts with the organism of which it is a component. These invariant relations are reflected, for example, in the life-long stability of profiles of reactivity of immunoglobulins formed by normal organisms (natural antibodies). Oral contacts with dietary proteins and the intestinal microbiota also result in steady states that lack the progressive quality of secondary-type reactivity. Autoreactivity (natural autoantibody and autoreactive T cell formation) is also stable and lacks the progressive quality of clonal expansion. Specific immune responses, currently regarded as the fundament of the operation of the immune system, may actually result from transient interruptions in this stable connectivity among lymphocytes. More permanent deficits in interconnectivity result in oligoclonal expansions of T lymphocytes, as seen in Omenn's syndrome and in the experimental transplantation of a suboptimal diversity of syngeneic T cells to immunodeficient hosts, which also have pathogenic consequences. Contrary to theories that forbid autoreactivity as potentially pathogenic, the physiology of the immune system is conservative and autoreactive. Pathology derives from failures of these conservative mechanisms.

Strategies for designing vaccines eliciting Th1 responses in humans

There is currently a major interest in designing vaccines capable of eliciting strong cellular immune responses. The induction of cytotoxic and Th1 helper cellular responses is for example highly desirable for vaccines targeting either chronic infectious diseases or cancers (therapeutic vaccines). Similarly, Th1 vaccines would be useful in redirecting inappropriate antigen-specific immune responses in patients with autoimmune diseases and allergies. Importantly, emerging technologies and a better understanding of the physiology of immune responses offer new avenues to rationally design such vaccines. Approaches based on the identification and selection of immunogens containing T cell epitopes can be used, together with epitope-enhancement strategies, to increase binding to MHC, or to improve recognition by T cell receptor complexes. Optimized immunogens can subsequently be presented to the immune system with appropriate vectors allowing to target professional antigen-presenting cells, such as dendritic cells. Such antigen presentation platforms can be used alone or in association, as part of mixed immunization regimens (heterologous prime-boosts), in order to elicit broad immune responses. The rational design of Th1 adjuvants can also benefit from our better understanding of the nature of proinflammatory signals leading to the initiation of both innate and adaptive immune effector mechanisms. Candidate Th1 vaccines (or components such as vectors or adjuvants) will have to be tested in exploratory clinical studies, implying a need for new assays and methods allowing to assess in a qualitative and quantitative manner low-frequency T cell responses in humans.

Modulating targeted adhesion of an ultrasound contrast agent to dysfunctional endothelium

The early stages of atherosclerosis are characterized by increased endothelial cell (EC) surface expression of leukocyte adhesion molecules (LAMs). Ultrasound detection of acoustically active LAM-targeted microbubbles might provide a means to noninvasively assess the functional status of the endothelium. Toward this end, a lipid-based perfluorobutane-filled microbubble was synthesized with various densities of anti-ICAM-1 monoclonal antibodies conjugated to the bubble shell. We hypothesized that modulating the surface antibody density would permit regulation of the adhesion characteristics of the microbubbles, and that microbubble adhesion would be dependent on local wall shear rate. Coverslips of cultured human coronary artery ECs were exposed to microbubbles with various surface antibody densities (1%, 5%, 10%, 50%, 75%, and 100% of maximum coverage) at various wall shear rates (100, 175, 250, 350, and 500 s-1) in a parallel plate perfusion chamber. ECs were either normal or activated by interleukin-1 beta to overexpress ICAM-1. Adhesion was greater to activated vs. normal ECs (p < 0.001), increased with increasing surface antibody density (p < 0.01), and decreased with increasing wall shear rate (p = 0.02). We conclude that shell antibody density and wall shear rate are critical parameters controlling differential microbubble adhesion. This phenomenon might ultimately permit imaging of clinically relevant LAM expression in vivo.

Characterization of an anti-MUC1 monoclonal antibody with potential as a cancer vaccine

The monoclonal antibody (MAb) AR20.5 is a murine MAb, generated against the tandem repeat protein backbone of the tumor-associated antigen MUC1. MAb AR20.5 reacts strongly with either the soluble form or the cell surface epitope of MUC1 on many human cancer cell lines. It also reacts with a 23-amino acid MUC1 peptide, E23, which includes the core tandem repeat sequence. Epitope mapping confirmed that MAb AR20.5 recognizes a minimum of six residues with the sequence DTRPAP. Inhibition of glycosylation of MUC1 resulted in decreased binding of MAb AR20.5 to cell surface MUC1, suggesting that MAb AR20.5 binding is carbohydrate dependent. The antibody was studied in a human PBL-SCID/beige mouse model to evaluate its effect on progression of NIH:OVARCAR-3 tumors. Tumor reduction was observed in mice injected with MAb AR20.5, but not in mice treated with control murine antibody or PBS (p < 0.001 and p < 0.05, respectively). An anti-tumor effect could also be demonstrated in a CB6F1 mouse model with the MUC1 transfectoma 413BCR.

Steered molecular dynamics investigations of protein function

Molecular recognition and mechanical properties of proteins govern molecular processes in the cell that can cause disease and can be targeted for drug design. Single molecule measurement techniques have greatly advanced knowledge but cannot resolve enough detail to be interpreted in terms of protein structure. We seek to complement the observations through so-called Steered Molecular Dynamics (SMD) simulations that link directly to experiments and provide atomic-level descriptions of the underlying events. Such a research program has been initiated in our group and has involved, for example, studies of elastic properties of immunoglobulin and fibronectin domains as well as the binding of biotin and avidin. In this article we explain the SMD method and suggest how it can be applied to the function of three systems that are the focus of modern molecular biology research: force transduction by the muscle protein titin and extracellular matrix protein fibronectin, recognition of antibody-antigene pairs, and ion selective conductivity of the K+ channel.

Crystal structure of the antigen-binding fragment of apoptosis-inducing mouse anti-human Fas monoclonal antibody HFE7A

Binding of Fas ligand to Fas induces apoptosis. The Fas-Fas ligand system plays important roles in many biological processes, including the elimination of autoreactive lymphoid cells. The mouse anti-human Fas monoclonal antibody HFE7A (m-HFE7A), which induces apoptosis, has been humanized based on a structure predicted by homology modeling. A version of humanized HFE7A is currently under development for the treatment of autoimmune diseases such as rheumatoid arthritis. For a deeper understanding of the protein engineering aspect of antibody humanization, for which information on the three-dimensional structure is essential, we determined the crystal structure of the m-HFE7A antigen-binding fragment (Fab) by X-ray crystallography at 2.5 A resolution. The main-chain conformation of the five loops in the six complementarity-determining regions (CDRs) was correctly predicted with root-mean-square deviations of 0.30-1.04 A based on a comparison of the crystal structure with the predicted structure. The CDR-H3 conformation of the crystal structure, which was not classified as one of the canonical structures, was completely different from that of the predicted structure but adopted the conformation which followed the "H3-rules." The results of charge distribution analysis of the antigen-binding site suggest that electrostatic interactions may be important for its binding to Fas.

Evidence of an affinity threshold for IgE-allergen binding in the percutaneous skin test reaction

BACKGROUND

Atopy is an aberrant immune response involving allergen-specific IgE production, though serum IgE concentration is not an entirely reliable diagnostic tool, particularly for epidemiological and genetic studies. There is no clear correlation between IgE and other indicators of atopy such as skin prick tests (SPT)s, and physiological associations are difficult to justify in cases with detectable IgE but negative SPT results.

OBJECTIVE

IgE reflects the number of molecules available to produce an atopic response, but the degree of the response is determined by the binding strength (affinity) between receptor-bound IgE and the allergen. We sought to determine if there was an association between binding affinity and SPT results in people with histories of atopy.

METHODS

Standard SPTs (whole allergen extracts) were administered to people with histories of sensitivities to ragweed and house dust mite. The concentrations and affinities of serum allergen-specific IgEs were determined using the purified allergens Amb a 1 and Der p 1.

RESULTS

There was a positive correlation between weal area and allergen-specific IgE among SPT-positive donors. However, for those individuals with detectable amounts of allergen-specific IgE, there was considerable overlap of IgE values between SPT-positive and -negative groups. Among sensitized donors, IgE-allergen interactions were characterized by two or three specific reactions of very high affinity (K(A) range 10(8) -10(11) M). Negative SPT reactions were associated with lowered IgE binding affinities to major allergens. This delimited two groups with atopic disorders: specific IgE(+)/ SPT(+) and specific IgE(+)/SPT(-).

CONCLUSION

The product of antibody affinity and concentration, which we define as antibody capacity (CAP = K(A) x IgE), is more informative with regard to describing allergen sensitivity than antibody concentration alone. Antibody binding capacity provides physiological evidence of atopy in some subjects who do not test positively by common methods and suggests an affinity threshold to produce a positive SPT reaction.

Molecular recognition in a reconstituted tumor cell membrane

The design of an immunoliposome system for molecular recognition using reconstituted, hydrogel-supported bilayer lipid membranes (sb-BLMs) is described. By monitoring the electrical properties, two kinds of recognition are feasible: (i) the human bladder tumor cells, Ej and its antibody BDI-1, the lifetime of the reconstituted membrane is 42 min; and (ii) the human rectum tumor cells, LOVO, the life of the reconstructed membrane is more than 40 min, the same as conventional BLM. Further, the anticancer drug, Adriamycin (Anticancer Res., 20 (2000) 1391), was shown to be effective in such reconstituted systems, the life of which is less than 5 min. In these experiments, the active ingredients of the Ej and LOVO cells were determined on reconstituted sb-BLMs. The key point is that the component part being recognized on the BLM must be kept in its native state.

Stereoselective recognition of monolayers of cholesterol, ent-cholesterol, and epicholesterol by an antibody

The interaction between a monoclonal antibody and four distinct monolayers with varying degrees of structural, chemical, and stereochemical similarity were studied and quantified. The antibody, raised and selected against cholesterol monohydrate crystals, interacts with cholesterol monolayers stereospecifically, but not enantiospecifically. Monolayers of ent-cholesterol molecules, which are chemically identical to cholesterol and whose structure is the exact mirror image of the cholesterol monolayer, interact with the antibody to the same extent as the cholesterol monolayers. The affinity of the antibody for both enantiomeric monolayers is extremely high. However, the antibody does not interact with monolayers of epicholesterol, which is an epimer of cholesterol: The hydroxy group in epicholesterol is in the 3alpha position rather than in the 3beta position, imposing a different angle between the hydroxy group and the rigid steroid backbone, and a different packing of the molecules. Monolayers of triacontanol, a long-chain primary aliphatic alcohol, interact with the antibody to a lesser extent than the cholesterol and ent-cholesterol monolayers, presumably due to the structural flexibility of the triacontanol molecule. The lack of chiral discrimination by the antibody is thus correlated to the level at which the chirality is exposed at the surface of the monolayers.

Differences between thyrotropin receptor antibody bioactivity and inhibition of 125I-bovine thyrotropin binding

Thyrotropin (TSHR) receptor antibodies that bind to the TSHR without stimulating the TSHR have been identified with a direct binding assay. Moreover, TSHR antibodies that exhibit thyroid epithelial cell stimulation without inhibition of 125I-bovine thyrotropin (bTSH) binding and vice versa have been described. These data suggest that stimulation or blocking of the TSHR by stimulating (TSAB) or blocking (TSBAB) TSHR antibodies could be possible without detectable bTSH-displacement activity. However, to date, possible differences between TSAB or TSBAB activity and inhibition of 125I-bTSH binding have not been systematically investigated. Therefore we compared inhibition of 125I-bTSH binding and TSAB or TSBAB activity of sera from 113 patients with Graves' disease treated with antithyroid drugs. To exclude the different assay conditions of previous investigations as possible confounding factors, we determined TSAB or TSBAB and inhibition of 125I-bTSH binding (TBIIW) with the same Chinese hamster ovary (CHO) cells expressing the human TSHR. Furthermore inhibition of 125I-bTSH binding was also determined as thyrotropin-binding inhibitory immunoglobulin (TBII) with solubilized porcine thyroid membranes (TRAK, Brahms, Berlin Germany) and the highly sensitive recombinant human TSH receptor assay (hTRAK, Brahms, Berlin Germany). Only 78% (54/69) of TSAB-positive and 78% (21/27) of TSBAB-positive sera detected with JP26 cells exhibit inhibition of 125I-bTSH binding measured as TBII or TBIIW. Furthermore, 59% (10/17) of sera without TSAB and TSBAB activity revealed inhibition of 125I-bTSH binding measured as TBII or TBIIW. We found significant differences between TSHR bioactivities (TSAB or TSBAB) and inhibition of 125I-bTSH binding. Moreover, there was no agreement between the detectable TSHR bioactivities (TSAB or TSBAB) and their detectable inhibition of 125I-bTSH binding. Therefore, it is very likely that TSH displacement by TSHR antibodies and stimulation or blocking of the TSHR by TSHR antibodies are different functions that do not need to occur together.

Inhibitory mechanism of aloe single component (alprogen) on mediator release in guinea pig lung mast cells activated with specific antigen-antibody reactions

We previously reported that the glycoprotein extracted from aloe strongly inhibited the mediator releases caused by the activation of guinea pig lung mast cells. Therefore, this study aimed to purify a single component that has an antiallergic effect from crude aloe extract and then to assess the effects of aloe single component (alprogen) on the mechanism of mediator releases caused by the mast cell activation. We purified aloe extracts by using various columns. We also purified mast cells from guinea pig lung tissues by using enzyme digestion, rough and discontinuous density Percoll gradient. Mast cells were sensitized with IgG(1) (anti-ovalbumin) and challenged with ovalbumin. Histamine was assayed by using a fluorometric analyzer and leukotrienes by radioimmunoassay. [Ca(2+)](i) level was analyzed by using a confocal laser scanning microscope. Protein kinase activity was determined by the protein phosphorylated with [gamma-(32)P]ATP. The phospholipase D activity was assessed by the labeled phosphatidylalcohol. The amount of mass 1,2-diacylglycerol (DAG) was measured by the [(3)H]DAG produced when prelabeled with [(3)H]myristic acid. Phospholipase A(2) activity was determined by measuring the lyso-phosphatidylcholine released from the labeled phospholipids. Alprogen significantly decreased histamine and leukotriene releases and blocked completely Ca(2+) influx during mast cell activation. The protein kinase C and phospholipase D activities were decreased by alprogen in dose-dependent manner. Alprogen inhibited mass DAG formation and the phospholipase A(2) activity during mast cell activation. The data suggest that alprogen purified from aloe inhibits multiple signals as well as blocking Ca(2+) influx caused by mast cells activated with specific antigen-antibody reactions and that then the inhibition of histamine and leukotriene release follows.

Operation of acoustic plate mode immunosensors in complex biological media

Acoustic wave based immunosensors have proven to facilitate the in situ detection of marker-free proteins in real time. However, the vast majority of these studies focuses on the interaction of a single type of antigen with immobilized receptors in pure buffer solutions. In an effort to evaluate the potential of acoustic plate mode immunosensors for operation in more complex biological environments, antigen/antibody reactions have been studied in pure buffer solution, in the presence of cells, and in human serum. It has been observed that the devices do not respond to cell adsorption and that antigen/antibody reactions can successfully be detected even if a thick layer of cells is deposited on the sensing surface. By varying the frequency of operation, it was shown that the sensitivity of the devices toward nonspecific protein adsorption is reduced at high frequencies of operation. Thus, spurious immunosensor response caused by non-specific adsorption processes can be suppressed by appropriately selecting device frequency. Using immunoglobulin G with minimum cross reactivity with human serum proteins, antigen/antibody reactions have also been monitored in human serum. While the observed frequency shifts are comparable to those measured in pure buffer solutions, the binding process is accompanied by additional acoustic loss, indicating changes in the viscoelastic properties of the interfacial layer.

Analysis of analyte-receptor binding kinetics for biosensor applications: an overview of the influence of the fractal dimension on the surface on the binding rate coefficient

An overview of fractal analysis is presented for analyte-receptor binding kinetics for different types of biosensor application. Data taken from the literature can be modelled by using (1) a single-fractal analysis, (2) a single- and a dual-fractal analysis, and (3) a dual-fractal analysis. Cases (2) and (3) represent a change in the binding mechanism as the reaction progresses on the surface. Predictive relationships developed for the binding rate coefficient as a function of the analyte concentration are of particular value because they provide a means by which the binding rate coefficients can be manipulated. Relationships are presented for the binding rate coefficients as a function of the fractal dimension, Df, or the degree of heterogeneity that exists on the surface. The binding rate coefficient is rather sensitive to the degree of heterogeneity, Df, that exists on the biosensor surface. For the examples analysed, the order of dependence of the binding rate coefficient on Df ranges from 1.4770 (k1), for the binding of intercalators and metabolites in solution to DNA immobilized at a positively charged surface, to 4.9434 for the binding of 5 nM nucleotide+GroEL in solution to GroES immobilized on a Ni2+-nitriloacetic acid sensor chip [Nieba, Nieba-Axmann, Persson, Hamalainen, Edebratt, Hansson, Lidholm, Magnusson, Karlsson and Pluckhun (1997) Anal. Biochem. 252, 217-228]. GroEl and GroES are two proteins (chaperones) which facilitate protein folding in the cell in an ATP-dependent manner [Hemmingson, Woolford, van der Vies, Tilly, Dennis, Georgopoulos, Henfrix and Ellis (1988) Nature (London) 333, 330-334]. The overview provides an overall analysis of the reaction parameters of importance observed and how they are influenced in antigen-antibody-binding kinetics for different biosensor applications. The predictive relationships presented provide further physical insights into the binding reactions on the surface, and should assist in enhancing biosensor performance. In general, the technique and the overview presented are applicable for the most part to other reactions occurring on different types of surface, for example cell-surface reactions.

Long-term serological follow up and cross-challenge studies in rhesus monkeys experimentally infected with hepatitis E virus

BACKGROUND/AIMS

The aims of this study were to examine the decline of IgG anti-HEV antibodies over a period of 7 years in rhesus monkeys experimentally infected with hepatitis E virus, and to assess the protectivity of these antibodies by challenging the monkeys with a heterologous isolate of hepatitis E virus, 5 years after the primary inoculation.

METHODS

Nine rhesus monkeys (six non-pregnant and three pregnant at the time of hepatitis E virus inoculation) were followed serologically and biochemically for 7 years post-inoculation. Based on regression analysis, estimated time for IgG anti-HEV titers to reach 1:100 or 1:50 was calculated. Three of the monkeys inoculated initially with AKL-90 isolate and challenged 2 years later with PUN-85 isolate of hepatitis E virus were rechallenged with KOL-91 isolate of the virus, 5 years post-primary inoculation. Evidence of viral replication was assessed by measuring serum alanine aminotransferase levels, excretion of the virus in feces or bile (reverse-transcription polymerase chain reaction) and rise in IgG anti-HEV titers (ELISA).

RESULTS

None of the challenged monkeys showed evidence of disease. In contrast to extensive replication of the virus in anti-HEV-negative control monkeys, limited replication was noted in one of the challenged monkeys. The estimated time for the titers to reach 1:100 or 1:50 varied from 3.15 to 44.9 years (19.4+/-11.6 years) and 6.9 to 84.3 years (35.4+/-21.3 years), respectively. Decline in titers was independent of the pregnancy status at the time of infection or reexposure of the monkeys to HEV CONCLUSION: The results show persistence of IgG anti-HEV antibodies for a long time and protectivity of low titered antibodies against reinfection, leading to disease even after intravenous exposure to a heterologous isolate of hepatitis E virus.

Induction of experimental autoimmune neuritis with peripheral myelin protein-22

Two myelin proteins, P2 basic protein and P0 glycoprotein, can induce experimental autoimmune neuritis (EAN), a model of human inflammatory neuropathy. We investigated whether peripheral nerve myelin protein-22 (PMP22), the gene for which is duplicated in hereditary motor sensory neuropathy type la, can also induce EAN. PMP22 cDNA produced by the reverse transcriptase-polymerase chain reaction from rat sciatic nerve was expressed in Escherichia coli as a fusion protein with glutathione-S-transferase (GST). Ten Lewis rats were immunized with purified PMP22 fusion protein (50-100 microg) and eight controls with the same amount of GST. Two additional animals were immunized with each of two peptides (250 microg) of the human PMP22 extracellular sequences. Animals were examined daily until 20 days following immunization, when they underwent neurophysiological examination. A serum sample was then taken, prior to perfusion with glutaraldehyde and removal of the sciatic nerves and cauda equina. PMP22-immunized animals developed antibodies to the fusion protein and five out of 10 developed limp tails. No changes were observed in controls immunized with GST or in animals immunized with peptide. The mean compound motor action potentials elicited in the foot muscles by stimulation of the sciatic nerve at the sciatic notch and of the tibial nerve at the ankle were significantly reduced in the PMP22-immunized group (P < 0.05). Spinal roots from the group of animals immunized with PMP22 showed sparse infiltration of mononuclear cells, oedema and demyelination. PMP22 now deserves consideration as an autoantigen in human acute inflammatory demyelinating polyradiculoneuropathy.

Molecular characterization of antipeptide antibodies against the 5-HT1A receptor: evidence for state-dependent antibody binding

Differential immunohistochemical labeling is often observed using different antibodies against the same protein. Two polyclonal antipeptide antibodies against the 5-HT1A receptor have been generated by our group. The S1A-170 (aa 170-186) and 258 (aa 258-274) are specific for sites in the second extracellular loop and third intracellular loop, respectively [E.C. Azmtia, I. Yu, H.M. Akbari, N. Kheck, P.M. Whitaker-Azmitia and D.R. Marshak, Antipeptide antibodies against the 5-HT1A receptor, J. Chem. Neuroanat., 5 (1992) 289-298]. Comparison of the labeling patterns of these two antibodies and other antipeptide antibodies against the 5-HT1A receptor revealed that although similar populations of cells were labeled, individual antibodies favor certain staining patterns. Immunocytochemistry and western blotting results of transfected cell lines and brain tissue revealed the following: (1) both the S1A-170 and S1A-258 are specific for the 5-HT1A receptor when used for immunocytochemistry in transfected HEK-293 and COS-1 cells; (2) when expressed in cultured cell lines, the 5-HT1A receptor is differentially glycosylated dependent on cell type, and the S1A-258 is specific for only certain species on immunoblots; and (3) the S1A-258 and L5B7 [M. Riad, S. El Mestikawy, D. Derge, H. Gozlan, and M. Hamon, Visualization and quantification of central 5-HT1A receptors with specific antibodies, Neurochem. Int., 4 (1991) 413-423] label common bands at 40 and 70 kDa on immunoblots of hippocampal proteins, but show opposite staining intensities. These results provide evidence for the immunocytochemical specificity of both the S1A-170 and S1A-258 and suggest that the discrepancies noted in immunohistochemistry may be due in part to different molecular conformations.

Neurite outgrowth is enhanced by anti-idiotypic monoclonal antibodies to the ganglioside GM1

Exogenously added gangliosides enhance sprouting, neurite outgrowth, and other neuronal activities; this effect may be initiated when a ganglioside binds to a membrane protein or when a ganglioside intercalates into the plasma membrane. To test whether binding to membrane proteins is sufficient for ganglioside-mediated activity, anti-idiotypic antibodies were generated that mimic the functional binding sites of the ganglioside GM1 as described by M. J. Riggott and W. D. Matthew (1996, Glycobiology, 6, 581-589). These anti-idiotypic antibodies are proteinaceous probes that model the biochemical and biological effects of gangliosides. Those anti-idiotypic ganglioside (AIG) monoclonal antibodies (mAb's) were selected based on their ability to bind a known GM1 binding protein, the beta-subunit of cholera toxin. These studies described neuronal cell surface proteins that were identified by immunocytochemistry and Western blotting using these AIG mAb's. Here we show that AIG mAb's mimic the functional properties of GM1 in that they facilitate neurite outgrowth from central and peripheral nervous system neurons in in vitro bioassays. In addition, AIG mAb binding modulates second messenger activity, suggesting that membrane protein binding alone is sufficient to invoke intracellular activation. The similarity in the pattern of protein tyrosine phosphorylation evoked by GM1 and the anti-idiotypic ganglioside antibodies suggests that the AIG mAb's modulate neurite outgrowth in a manner similar to that of GM1. Because antibodies cannot intercalate into the plasma membrane, these results suggest that the ganglioside GM1 can mediate neuronal cellular activity by binding to cell surface proteins.

Influence of diffusion to fractal surfaces on the binding kinetics for antibody-antigen, analyte-receptor, and analyte-receptorless (protein) systems

The diffusion-limited binding kinetics of antigen-antibody, ligand-receptor, analyte-receptorless systems for biosensor applications is analyzed within a fractal framework. The analysis presented applies equally well to these types of systems. For example, for the binding of 2-(p-toluidiny)-naphthalene-6-sulfonic acid (2,6-TNS) to beta-cyclodextrin (ligand-receptor system) immobilized on a fiber-optic base inclusate biosensor, an increase in temperature from 4 to 30 degrees C leads to an increase in the fractal dimension, D1 and to a decrease in the binding rate coefficient, k1. For the binding of TRITC-labeled low-density proteins (LDL) directly to an optical fiber-based sensor (analyte-receptorless system), an increase in the LDL concentration from 5 to 50 micrograms ml-1 in solution leads to a decrease in the fractal dimension, D1 and to an increase in the binding rate coefficient, k1. Also, during the binding of human chorionic gonadotropin (hCG) to anti-hCG antibody immobilized on a HPLC column (antigen-antibody system), an increase in temperature from 4 to 50 degrees C leads to an increase in the fractal dimension, D1 and in the binding rate coefficient. k1. The different examples analyzed and presented together for the three different types of systems provide one means of a 'unified analysis,' and a method by which the forward binding rate coefficient, k1 may be controlled, that is, by changing the fractal dimension or 'disorder' on the surface. The analysis should assist in improving the stability, sensitivity, and response time of biosensors wherein different types of binding systems are utilized in the analysis method. More-or-less all of the treatment presented should be applicable to the above types of binding systems occurring in non-biosensor applications also. However, the single-fractal analysis is unable to describe the data over the full time course of some of the experiments.

Molecular interaction of growth hormone with two monoclonal antibodies recognizing distinct epitopes

Two monoclonal antibodies (mAb), designated PS-7.6 and PS-11.2, were generated against recombinant porcine growth hormone (pGH) and shown to enhance the hormonal activity in promoting the growth of animals. The mAb were compared and their functional relationship investigated. It was demonstrated by radioimmunoassay that PS-11.2 did not compete, but rather enhanced binding of 125I-pGH tracer to PS-7.6, suggesting that both mAb recognized distinct epitopes and also were additive in their antigen bindings. Surface plasmon resonance analysis using optical BIAcore technology (Pharmacia Biosensor, Piscataway NJ, USA) provided additional data to support this idea because pGH, after being captured by PS-11.2, remained capable of interacting with PS-7.6. An anti-idiotypic mAb was employed and shown to interact with PS-7.6 but not PS-11.2, implying that the differences in the Fab variable regions of these two mAb might contribute to their epitope specificity. Binding kinetics were determined by the BIAcore and the individual affinities of PS-7.6 and PS-11.2 to pGH were 6.8 x 10(-8) and 1.2 x 10(-9) mol/L, respectively. When these mAb were sequentially subjected to the BIAcore, however, their affinities decreased by approximately 100-fold. Therefore, binding of pGH with one mAb significantly impaired a subsequent interaction with another mAb despite the fact that both mAb targeted different epitopes. Hypophysectomized rats were used for functional analysis and pGH was active in promoting growth of these GH-deficient animals. The hormonal effect was further improved by incubating pGH with either PS-7.6 or PS-11.2 prior to administration. However, enhancement by individual mAb was completely abolished when pGH was treated with both mAb together, indicating their unpredictable biological interference with each other. Therefore, the present findings clearly demonstrate that although PS-7.6 and PS-11.2 recognize separate epitopes, their individual interactions with pGH are closely interrelated both immunologically and biologically.

Generation of a panel of related human scFv antibodies with high affinities for human CEA

BACKGROUND

A human single chain Fv (scFv) specific for human carcinoembryonic antigen (CEA) has been isolated from a 2.0 x 10(9) phage display library from unimmunised human donors. The dissociation constant of the scFv has been measured by surface plasmon resonance (SPR) and found to be 7.7 x 10(-9) M, with an off-rate component of 6.2 x 10(-3) s-1. In order to investigate directly whether increased affinity leads to improved targeting of CEA-positive tumours, this scFv has been affinity matured by both targeted mutagenesis of the CDRs of heavy and light chains, and by light chain shuffling.

STUDY DESIGN

A partial randomisation scheme, biased towards amino acids commonly found as somatic mutations of germline antibody sequences, was used for directed diversification of VH and VL CDR3s. Diversification of the entire VL region was also introduced by light chain shuffling of the parental anti-CEA scFv. Selection of the mutagenised repertoires was carried out to enrich for antibodies with a reduced koff.

RESULTS

Sequencing the selected clones identified a number of amino acid changes in the VH CDR3, one of which gave a four-fold reduction in koff. Stringent selection of the light chain shuffled library resulted in several clones with a two- to three-fold reduction in koff. It has been possible to combine the selected changes from both mutagenesis approaches by using the mutagenised heavy chain and a light chain derived by shuffling to give a human scFv with a dissociation constant for human CEA of 6.0 x 10(-10) M.

CONCLUSION

A panel of human anti-CEA scFvs has been generated with differing dissociation constants for antigen, which will allow the correlation between tumour targeting efficiency in relation to binding affinity to be assessed directly. The scFv panel will be valuable in the optimisation of human antibodies for immunotherapy.

Alteration of glomerular permeability to macromolecules induced by cross-linking of beta 1 integrin receptors

Altered glomerular epithelial cell attachment to the glomerular basement membrane is an important pathogenetic factor in increased glomerular permeability to proteins. We have previously presented evidence that antibodies reactive with integrin matrix receptors on glomerular epithelial cells inhibit adhesion of these cells and may be involved in the production of proteinuria in vivo. Therefore, we utilized intact glomeruli in an in vitro system to directly assess the effect of anti-beta 1-integrin antibody on glomerular permeability. Permeability to albumin (Palb) was calculated from the volume response of glomeruli to a transcapillary oncotic gradient. Anti-beta 1-integrin increased Palb in a dose- and time-dependent manner. Palb was increased to 0.70 +/- 0.05 whereas normal rabbit IgG had no effect (0.10 +/- 0.04). F(ab')2 fragments of antibody increased Palb to a similar degree whereas Fab fragments had no effect (0.10 +/- 0.06). Cross-linking of Fab fragments, however, with a second antibody restored their ability to increase Palb (0.60 +/- 0.09), demonstrating the importance of integrin cross-linking in producing the observed effect. Intact, F(ab')2 and Fab fragments of anti-beta 1 antibody all inhibited adhesion of glomerular epithelial cells to fibronectin, laminin, and types I and IV collagen, although the degree of inhibition by Fab fragments was significantly less on collagens. No cytotoxic effects were observed with anti-beta 1 antibody or its fragments. These results suggest that antibodies to integrin matrix receptors on glomerular cells alter cell interactions with the glomerular basement membrane and lead to increased glomerular permeability to proteins via a process that is initiated by integrin cross-linking rather than through simple interference with cell adhesion per se.

Analysis of kinetic data of antibody-antigen interaction from an optical biosensor by exponential curve fitting

An optical biosensor system employing a resonant mirror (RM), with a stirred cuvette has been used to follow the interaction of a recombinant antibody fragment with its antigen, hen egg lysozyme. The data generated by the biosensor were analysed in order to determine the kinetic constants for the interaction using a linear transform (derivative analysis). For comparison the data were also analysed using an exponential curve fitting routine. It was demonstrated that the exponential curve fitting method produced results which were in agreement with the existing linear transform method. It was also shown that early fitting of the association phase response, using the exponential curve fitting routine between 0 and 70 s after sample addition, yielded sufficient information to provide a prediction of Kon. The potential use of the optical biosensor for the rapid monitoring of protein production and purification is discussed.

Detection and localization of individual antibody-antigen recognition events by atomic force microscopy

A methodology has been developed for the study of molecular recognition at the level of single events and for the localization of sites on biosurfaces, in combining force microscopy with molecular recognition by specific ligands. For this goal, a sensor was designed by covalently linking an antibody (anti-human serum albumin, polyclonal) via a flexible spacer to the tip of a force microscope. This sensor permitted detection of single antibody-antigen recognition events by force signals of unique shape with an unbinding force of 244 +/- 22 pN. Analysis revealed that observed unbinding forces originate from the dissociation of individual Fab fragments from a human serum albumin molecule. The two Fab fragments of the antibody were found to bind independently and with equal probability. The flexible linkage provided the antibody with a 6-nm dynamical reach for binding, rendering binding probability high, 0.5 for encounter times of 60 ms. This permitted fast and reliable detection of antigenic sites during lateral scans with a positional accuracy of 1.5 nm. It is indicated that this methodology has promise for characterizing rate constants and kinetics of molecular recognition complexes and for molecular mapping of biosurfaces such as membranes.

Autoantibodies to T-cell receptor beta chains in human heart transplantation: epitope and spectrotype analyses and kinetics of response

Autoantibodies against T-cell receptors have been found in two alloimmunization situations in humans: renal transplantation and pregnancy. We carried out longitudinal studies of human heart transplant recipients monitoring their autoantibody production to a recombinant single chain T-cell receptor V alpha/V beta construct, a set of nested, overlapping peptides duplicating the complete covalent structure of an individual T-cell receptor beta chain and a set of peptides duplicating the first complementarity determining segments of 24 distinct human V beta gene products in order to define the time course, epitope specificity and recognition heterogeneity of the response. Autoantibodies against intact and peptide-defined V beta and C beta determinants were generated following human heart allotransplantation. The responses generally show an increase following transplantation that subsequently decreases with time, a result which is consistent with a single immunization. However, some patients showed elevated responses as long as 12 months following the transplant. Autoantibody anti-CDR1 spectrotype analyses detected individual differences among patients, but 5 of 8 patients characterized in detail showed elevated IgG binding to CDR1 peptide epitopes of V beta 6.1, 21.1 and 22.1 gene products. Autoantibodies to CDR1 epitopes of V beta 7.1 and 8.1 were high pretransplant and remained high, although the relative increases with respect to the pretransplant values were not as impressive as those for the above CDR1 epitopes and others usually present in low quantity, e.g. anti-V beta 2.1, 3.1 and 24.1. Although there was great disparity between the MHC haplotypes of donors and recipients, and individual differences among patients, the degree of restriction in the autoantibody response was surprising and suggests a common step in recognition and regulation of the response to allografts.

[Role of antigen-antibody reaction in pulmonary hypertensive reaction after antigen challenge]

Pulmonary arterial pressure, airway pressure, and lung weight increase were studied after antigen (human O-N type erythrocytes) challenge in isolated-perfused sensitized rabbit lungs. To investigate whether these hemodynamic changes are mainly caused by antigen-antibody reaction or by the other mechanisms, we measured changes of pulmonary arterial and airway pressures, and lung weight gain after antigen challenge in perfused nonsensitized rabbit lungs. Thirteen nonsensitized rabbits were divided into 2 groups; in N group (n = 5), antigen was given into Krebs Hanseleit perfusate; in Ab group (n = 8), antibody was given into reservoir 30 min prior to antigen challenge. Pulmonary arterial pressure in Ab group was higher than in N group after antigen challenge. Maximal increase in pulmonary arterial pressure after antigen challenge depended on agglutinin titer of antibody in perfusate (delta Ppa = 0.068 x [titer]-0.146, r2 = 0.929). However, there were no significant differences between the two groups in changes of airway pressure and lung weight gain after antigen challenge. Although agglutinin titer of perfusate in Ab group was higher than our previous study, pulmonary hypertensive reaction to antigen in Ab group was significantly lower. It is concluded that the other mechanism besides antigen-antibody reaction itself can be responsible for hemodynamic changes after antigen challenge.

Protein motion and lock and key complementarity in antigen-antibody reactions

Antibodies possess a highly complementary combining site structure to that of their specific antigens. In many instances their reactions are driven by enthalpic factors including, at least in the case of the reaction of monoclonal antibody D1.3 with lysozyme, enthalpy of solvation. They require minor structural rearrangements, and their equilibrium association constants are relatively high (10(7)-10(11) M-1). By contrast, in an idiotope--anti-idiotope (antibody-antibody) reaction, which is entropically driven, the binding equilibrium constant is only 1.5 x 10(5) M-1 at 20 degrees C. This low value results from a slow association rate (10(3) M-1 s-1) due to a selection of conformational states that allow one of the interacting molecular surfaces (the idiotope on antibody D1.3) to become complementary to that of the anti-idiotopic antibody. Thus, antibody D1.3 reacts with two different macromolecules: with its specific antigen, hen egg lysozyme, and with a specific anti-idiotopic antibody. Complementarity with lysozyme is closer to a "lock and key" model and results in high affinity (2-4 x 10(8) M-1). That with the anti-idiotopic antibody involves conformational changes at its combining site and it results in a lower association constant (1.5 x 10(5) M-1). Thus, an "induced fit" mechanism may lead to a broadening of the binding specificity but with a resulting decrease in the intrinsic binding affinity which may weaken the physiological function of antibodies.

Analysis of the specificity of anti-PM-Scl autoantibodies

OBJECTIVE

To compare the specificity of anti-PM-Scl autoantibodies in serum samples from 43 patients with myositis, scleroderma, or both.

METHODS

Anti-PM-Scl immunoprecipitates from HeLa cell extract were used as antigen for immunoblot analyses to determine the antigenic components. A series of complementary DNA fragments was expressed in Escherichia coli for immunoblot examination of the reaction with the 100-kd protein.

RESULTS

The immunoblot against immunoprecipitates was sensitive and specific for detecting reactions with components of the PM-Scl antigen: 42 of 43 sera (97.7%) reacted with the 100-kd, 27 of 43 (62.8%) with the 70-kd, and 5 of 43 (11.6%) with the 37-kd protein (not previously recognized as antigenic). Forty-one sera reacted with N-terminal protein S1 (amino acids 11-437), 39 with central protein S2 (amino acids 439-749), and 24 with C-terminal protein S3 (amino acids 750-882). Of 42 sera tested, 28 (66.7%) reacted most strongly with S1, and 6 (14.3%) reacted most strongly with S2. Absorption studies implied additional, conformational epitopes not present on the bacterially expressed antigen.

CONCLUSION

There was an overall similarity in reactivity to the PM-Scl antigen, but there were differences in the reactivity to the 70-kd and 37-kd proteins, as well as in the relative strength of the reactivity to the S2 protein.

Monitoring the formation of soluble immune complexes composed of idiotype and anti-idiotype antibodies by electron microscopy

We have previously used immunoelectron microscopy (IEM) to generate a three-dimensional map of idiotypic (Id) and isotypic epitopes on the Fab arms of HGAC 39 (Roux et al., 1987, Proc. natn. Acad. Sci. U.S.A. 84, 4984-4988), a mouse IgG3 monoclonal antibody (Mab). In this report, we analyse the geometry of the various types of immune complexes formed by the interaction of HGAC 39 with Mab directed against four mapped epitopes. Moreover, by sampling of reaction mixtures over time, we show that the kinetics of each of the subpopulations of immune complexes, as defined by geometric configuration, can be determined. The data show that for each antibody (Ab)-HGAC 39 combination the rate of immune complex formation was greatest during the first 1.5-3.5 min but that additional complexes formed through the remainder of the half hour assay period. As anticipated, complexes composed of even number units predominated (primarily dimers and tetramers) and most of these were in the form of closed rings. The data also suggest that the location and orientation of the epitopes on HGAC 39 to which the monoclonal antibodies were bound has an influence on the types of immune complexes generated. Specifically we observed that those anti-idiotype Abs that bind to the distal tip of Fab arms (i.e. in the CDR) are less likely to produce bivalently associated ringed dimers than antibodies that bind to epitopes that are proximal to the CDR and that project laterally from the surface of the Fab arms. These data are interpreted in terms of restrictions on hinge mediated flexibility and steric inhibition between adjacent Fab arms on HGAC 39.

Variable domain-identical antibodies exhibit IgG subclass-related differences in affinity and kinetic constants as determined by surface plasmon resonance

We have analysed the binding of variable domain-identical mouse monoclonal antibodies (mAb) of the IgG3, IgG1 and IgG2b subclasses, as well as F(ab')2 fragments derived from the IgG3 and IgG1 mAb, to a multivalent glycoprotein target. Using a biosensor device (BIAcore, Pharmacia Biosensor) that measures the mass of the antibody (or other receptor molecule) deposited on a sensor chip displaying the relevant epitopes, we found that the IgG3 mAb binds more effectively than the other antibody species at a high but not a low epitope density. The greater functional affinity associated with the IgG3 mAb, at high epitope density, was correlated with both slower dissociation rate constants and faster association rate constants in comparison with the IgG1 and IgG2b mAb and the F(ab')2 fragments derived from the IgG3 and IgG1 mAb. Evidence for slower dissociation kinetics for the IgG3 mAb versus the IgG1 and IgG2b mAb was also obtained by ELISA and flow cytometry. These results demonstrate that: (1) differences in heavy chain constant (CH) domains can significantly influence apparent functional affinity for multivalent antigen, as determined without the use of covalently modified primary or secondary antibodies; (2) differences in CH domains can alter both association and dissociation rate constants for interactions between IgG antibodies and multivalent antigen; and (3) these effects of CH domains depend on epitope density. The effect of constant region differences on the apparent association rate constants suggests new approaches for achieving better binding or functional effectiveness through antibody engineering.

Inhibitory effects of (4-alkoxy-2, 3, 6-trimethylphenyl) glycopyranosides on histamine release induced by antigen-antibody reaction

The inhibitory effects of newly synthesized 4-alkoxy-2, 3, 6-trimethylphenyl D-glycopyranosides on histamine release induced by antigen-antibody reaction were examined. Among the compounds tested, 4-hexoxy-2, 3, 6-trimethylphenyl alpha-D-mannopyranoside exhibited the strongest inhibitory effect. Furthermore, 4-hexoxy-2, 3, 6-trimethylphenyl alpha-D-glucopyranoside and alpha-D-galactopyranoside markedly inhibited antigen-induced histamine release, and their activities were more potent than those of the corresponding beta-anomers. These results suggest that these compounds may possess excellent anti-allergic activities.