VIPase autoantibodies in Fas-defective mice and patients with autoimmune disease

Catalytic antibody (catabody) platform for age-associated amyloid disease: From Heisenberg's uncertainty principle to the verge of medical interventions

Quantum mechanics-based design of useful catalytic antibodies (catabodies) failed because of the uncertain structure of the dynamic catalyst-substrate complex. The Catabody Platform emerged from discovery of beneficial germline gene catabodies that hydrolyzed self-proteins by transient covalent pairing of the strong catabody nucleophile with a weak target protein electrophile. Catabodies have evolved by Darwinian natural selection for protection against misfolded self-proteins that threatened survival by causing amyloid disease. Ancient antibody scaffolds upregulate the catalytic activity of the antibody variable (V) domains. Healthy humans universally produce beneficial catabodies specific for at least 3 misfolded self-proteins, transthyretin, amyloid β peptide and tau protein. Catabody are superior to ordinary antibodies because of catalyst reuse for thousands of target destruction cycles with little or no risk of causing inflammation, a must for non-toxic removal of abundant targets such as amyloids. Library mining with electrophilic target analogs (ETAs) isolates therapy-grade catabodies (fast, specific). Ex vivo- and in vivo-verified catabodies specific for the misfolded protein are available to dissolve brain, cardiac and vertebral amyloids. Immunization with ETAs overcomes important ordinary vaccine limitations (no catabody induction, poor immunogenicity of key target epitopes). We conceive electrophilic longevity vaccines that can induce catabody synthesis for long-lasting protection against amyloid disease.

Vasoactive intestinal peptide degradation might influence Interleukin-17 expression in cardiac chagasic patients

The vasoactive intestinal peptide (VIP) expression is lower in cardiac chagasic patients and is related to worse cardiac function. The reduction of VIP in patients with Chagas disease may be a result of its enhanced degradation. To test this hypothesis, the tryptase and chymase expression was evaluated. We also related VIP levels with interleukin-17 (IL-17) expression since VIP may modulate IL-17 production. Plasma levels of chymase were higher in chagasic patients. Conversely, VIP/chymase and VIP/tryptase ratios were lower in chagasic patients when compared to non-infected individuals. Besides, the VIP/chymase ratio was lower in chagasic cardiac patients in comparison with the indeterminate group. A positive correlation between tryptase and chymase levels was observed in chagasic cardiac patients. In relation to IL-17, we observed a higher expression of this cytokine in the cardiac form of the disease than in the indeterminate form. IL-17/VIP ratio was higher in the cardiac form in comparison with non-infected or indeterminate form. These results suggest that the low levels of VIP observed in chagasic patients could be due to an increased production of chymase and/or to the additive effect of the interaction between chymase and tryptase in the cardiac form. Moreover, the decreased VIP expression may contribute to the increase of IL-17 in chagasic cardiac patients.

Vasoactive intestinal peptide gene polymorphisms, associated with its serum levels, predict treatment requirements in early rheumatoid arthritis

We previously reported that early arthritis (EA) patients with low vasoactive intestinal peptide (VIP) serum levels demonstrate a worse clinical disease course. In this study, we analysed whether variants in the VIP gene correlated with its serum levels and clinical EA parameters. The VIP gene was sequenced in patients with extremely high/low VIP levels, measured by enzyme immunoassay. Sixteen single nucleotide polymorphisms (SNPs) were differentially distributed between both groups, which were subsequently genotyped in two patients’ sets. We observed that patients with rs688136 CC genotype showed higher VIP levels in both discovery (n = 91; p = 0.033) and validation populations (n = 131; p = 0.007). This effect was attenuated by the presence of minor alleles rs35643203 and rs12201140, which showed a clear trend towards low VIP level association (p = 0.118 and p = 0.049, respectively). Functional studies with miR-205-5p, which has a target site in the 3′ UTR close to rs688136, revealed a miRNA-mediated regulatory mechanism explaining the higher VIP gene expression in homozygous patients. Moreover, patients with an rs688136 CC genotype and no minor alleles of the other polymorphisms required less treatment (p = 0.009). We concluded that the identification of polymorphisms associated with VIP serum levels would complement the clinical assessment of the disease severity in rheumatoid arthritis patients.

The neuropeptide vasoactive intestinal peptide: direct effects on immune cells and involvement in inflammatory and autoimmune diseases

Neuropeptides represent an important category of endogenous contributors to the establishment and maintenance of immune deviation in the immune-privileged organs such as the CNS and in the control of acute inflammation in the peripheral immune organs. Vasoactive intestinal peptide (VIP) is a major immunoregulatory neuropeptide widely distributed in the central and peripheral nervous system. In addition to neurones, VIP is synthesized by immune cells which also express VIP receptors. Here, we review the current information on VIP production and VIP-receptor-mediated effects in the immune system, the role of endogenous and exogenous VIP in inflammatory and autoimmune disorders and the present and future VIP therapeutic approaches.

A novel molecular analysis of genes encoding catalytic antibodies

Among the numerous questions remaining opened about catalytic antibodies (abzymes), the understanding of the origin of the genes encoding them is of vital significance. An original statistical analysis of genes encoding abzymes is described in the present report. Results suggested that these genes display a high conservation degree with their germline counterpart and a limited number of amino acid changes. Hence, on the contrary with high-affinity antibodies, maturation process by accumulation of somatic hypermutations is not required for the catalytic function. We demonstrated that despite a weak somatic mutation rate, the physicochemical properties of mutated amino acid (AA) are predominantly dissimilar with that of the germline AA. Further, we developed a novel approach in order to analyze the nature of genes encoding catalytic antibodies. For the first time, an unexpected and significant high level expression of rare gene subgroups was noticed and emphasized. The data described in this paper would lay the foundation for future studies about origin of genes encoding catalytic antibodies.

Constitutive production of catalytic antibodies to a Staphylococcus aureus virulence factor and effect of infection

Antibodies that recognize microbial B lymphocyte superantigenic epitopes are produced constitutively with no requirement for adaptive immune maturation. We report cleavage of the Staphylococcus aureus virulence factor extracellular fibrinogen-binding protein (Efb) by catalytic antibodies produced with no exposure to the bacterium and reduction of the catalytic antibody activity following infection. IgG catalytic antibodies that specifically hydrolyzed Efb via a nucleophilic catalytic mechanism were found in the blood of healthy humans and aseptic mice free of S. aureus infection. IgG hydrolyzed peptide bonds on the C-terminal side of basic amino acids, including a bond located within the C3b-binding domain of Efb. Efb digested with the IgG lost its ability to bind C3b and inhibit complement-dependent antibody-mediated red blood cell lysis. In addition to catalysis, the IgG expressed saturable Efb binding activity. IgG from S. aureus-infected mice displayed reduced Efb cleaving activity and increased Efb binding activity compared with uninfected controls, suggesting differing effects of the infection on the antibody subsets responsible for the two activities. IgG from children hospitalized for S. aureus infection also displayed reduced Efb cleavage compared with healthy children. These data suggest a potential defense function for constitutively produced catalytic antibodies to a putative superantigenic site of Efb, but an adaptive catalytic response appears to be proscribed.

Vasoactive intestinal peptide: a neuropeptide with pleiotropic immune functions

Vasoactive intestinal peptide (VIP), a 28-amino acid neuropeptide/neurotransmitter, is widely distributed in both the central and peripheral nervous system. VIP is released by both neurons and immune cells. Various cell types, including immune cells, express VIP receptors. VIP has pleiotropic effects as a neurotransmitter, immune regulator, vasodilator and secretagogue. This review is focused on VIP production and effects on immune cells, VIP receptor signaling as related to immune functions, and the involvement of VIP in inflammatory and autoimmune disorders. The review addresses present clinical use of VIP and future therapeutic directions.

Neuropeptides as pleiotropic modulators of the immune response

Although necessary to eliminate pathogens, inflammation can lead to serious deleterious effects in the host if left unchecked. During the inflammatory response, further damage may arise from potential autoimmune responses occurring when the immune cells and molecules that respond to pathogen-derived antigens also react to self-antigens. In this sense, the identification of endogenous factors that control exacerbated immune responses is a key goal for the development of new therapeutic approaches for inflammatory and autoimmune diseases. Some neuropeptides that are produced during the ongoing inflammatory response have emerged as endogenous anti-inflammatory agents that could collaborate in tuning the balanced steady state of the immune system. These neuropeptides participate in maintaining immune tolerance through two distinct mechanisms: by regulating the balance between pro-inflammatory and anti-inflammatory factors, and by inducing the emergence of regulatory T cells with suppressive activity against autoreactive T cell effectors. Indeed, a functioning neuropeptide system contributes to general health, and alterations in the levels of these neuropeptides and/or their receptors lead to changes in susceptibility to inflammatory and autoimmune diseases. Recently, we found that some neuropeptides also have antimicrobial and antiparasitic actions, suggesting that they could act as primary mediators of innate defense, even in the most primitive organisms. In this review, we use the vasoactive intestinal peptide as example of an immunomodulatory neuropeptide to summarize the most relevant data found for other neuropeptides with similar characteristics, including adrenomedullin, urocortin, cortistatin and ghrelin.

Toward effective HIV vaccination: induction of binary epitope reactive antibodies with broad HIV neutralizing activity

We describe murine monoclonal antibodies (mAbs) raised by immunization with an electrophilic gp120 analog (E-gp120) expressing the rare ability to neutralize genetically heterologous human immunodeficiency virus (HIV) strains. Unlike gp120, E-gp120 formed covalent oligomers. The reactivity of gp120 and E-gp120 with mAbs to reference neutralizing epitopes was markedly different, indicating their divergent structures. Epitope mapping with synthetic peptides and electrophilic peptide analogs indicated binary recognition of two distinct gp120 regions by anti-E-gp120 mAbs, the 421-433 and 288-306 peptide regions. Univalent Fab and single chain Fv fragments expressed the ability to recognize both peptides. X-ray crystallography of an anti-E-gp120 Fab fragment revealed two neighboring cavities, the typical antigen-binding cavity formed by the complementarity determining regions (CDRs) and another cavity dominated by antibody heavy chain variable (V(H)) domain framework (FR) residues. Substitution of the FR cavity V(H) Lys-19 residue by an Ala residue resulted in attenuated binding of the 421-433 region peptide probe. The CDRs and V(H) FR replacement/silent mutation ratios exceeded the ratio for a random mutation process, suggesting adaptive development of both putative binding sites. All mAbs studied were derived from V(H)1 family genes, suggesting biased recruitment of the V gene germ line repertoire by E-gp120. The conserved 421-433 region of gp120 is essential for HIV binding to host CD4 receptors. This region is recognized weakly by the FR of antibodies produced without exposure to HIV, but it usually fails to induce adaptive synthesis of neutralizing antibodies. We present models accounting for improved CD4-binding site recognition and broad HIV neutralizing activity of the mAbs, long sought goals in HIV vaccine development.

Generating tolerogenic dendritic cells with neuropeptides

Induction of antigen-specific tolerance is critical to prevent autoimmunity, to maintain immune homeostasis, and to achieve transplant tolerance. In addition to their classic role as sentinels of the immune response, dendritic cells (DCs) play important roles in maintaining peripheral tolerance through the induction/activation of regulatory T (Treg) cells. The possibility of generating tolerogenic DCs opens new therapeutic perspectives in autoimmune and inflammatory diseases. Characterizing endogenous factors that contribute to the development of tolerogenic DCs is highly relevant. Some neuropeptides that are produced during the ongoing inflammatory response have emerged as endogenous anti-inflammatory agents that participate in the regulation of the processes that ensure self-tolerance. Here, we examine the latest research findings indicating that the role of these neuropeptides in immune tolerance is partially mediated through differential effects on DC functions, which depend on the differentiation and activation states. Importantly, neuropeptides such as vasoactive intestinal peptide, pituitary adenylate cyclase-activating polypeptide, and melanocyte-stimulating hormone have demonstrated an ability to induce tolerogenic DCs with the capacity to generate CD4 and CD8 Treg cells. The possibility of generating or expanding ex vivo tolerogenic DCs with neuropeptides indicates the therapeutic potential for autoimmune diseases and graft-versus-host disease after allogeneic transplantation in humans.

Anti-inflammatory neuropeptides: a new class of endogenous immunoregulatory agents

Resolution of inflammation and induction of immune tolerance are essential to stabilize immune homeostasis and to limit the occurrence of exacerbated inflammatory and autoimmune conditions. Multiple mechanisms act together to ensure the re-establishment of immune homeostasis and maintenance of tolerance. The identification of endogenous factors that regulate these processes is crucial for the development of new therapies for inflammatory/autoimmune conditions. Neuropeptides produced during an ongoing inflammatory response emerged as endogenous anti-inflammatory agents that participate in processes leading to the resolution of inflammation and maintenance of tolerance. Anti-inflammatory neuropeptides and hormones such as vasoactive intestinal peptide, urocortin, adrenomedullin, melanocyte stimulating hormone, ghrelin, and cortistatin have beneficial effects in a variety of experimental inflammatory and autoimmune models. Their therapeutic effect has been attributed to their capacity to downregulate innate immunity, to inhibit antigen-specific T(H)1-driven responses, and to generate regulatory T cells. Finally, some of these neuropeptides have been identified as mediators of innate defense acting as natural antimicrobial peptides. Here we present the research findings in the neuropeptide immunoregulatory field, and examine possible therapies based on anti-inflammatory neuropeptides and hormones as a new pharmacologic platform.

Endogenous anti-inflammatory neuropeptides and pro-resolving lipid mediators: a new therapeutic approach for immune disorders

Identification of the factors that regulate the immune tolerance and control the appearance of exacerbated inflammatory conditions is crucial for the development of new therapies of inflammatory and autoimmune diseases. Although much is known about the molecular basis of initiating signals and pro-inflammatory chemical mediators in inflammation, it has only recently become apparent that endogenous stop signals are critical at early checkpoints within the temporal events of inflammation. Some neuropeptides and lipid mediators that are produced during the ongoing inflammatory response have emerged as endogenous anti-inflammatory agents that participate in the regulation of the processes that ensure self-tolerance and/or inflammation resolution. Here we examine the latest research findings, which indicate that neuropeptides participate in maintaining immune tolerance in two distinct ways: by regulating the balance between pro-inflammatory and anti-inflammatory factors, and by inducing the emergence of regulatory T cells with suppressive activity against autoreactive T-cell effectors. On the other hand, we also focus on lipid mediators biosynthesized from omega-3 and omega-6 polyunsaturated fatty-acids in inflammatory exudates that promote the resolution phase of acute inflammation by regulating leucocyte influx to and efflux from local inflamed sites. Both anti-inflammatory neuropeptides and pro-resolving lipid mediators have shown therapeutic potential for a variety of inflammatory and autoimmune disorders and could be used as biotemplates for the development of novel pharmacologic agents.

Genetic association of vasoactive intestinal peptide receptor with rheumatoid arthritis: altered expression and signal in immune cells

OBJECTIVE

Vasoactive intestinal peptide (VIP) has been shown to be one of the endogenous factors involved in the maintenance of immune tolerance. Administration of VIP ameliorates clinical signs in various experimental autoimmune disorders. This study was undertaken to investigate whether the exacerbated inflammatory autoimmune response in rheumatoid arthritis (RA) might result directly from altered expression and/or signaling of VIP receptors in immune cells.

METHODS

The effect of specific agonists of different VIP receptors on collagen-induced arthritis in mice was investigated by clinical and histologic assessment and measurement of cytokine and chemokine production. Expression of VIP receptor type 1 (VPAC1) in synovial cells and monocytes from RA patients was determined by flow cytometry. Potential associations of VPAC1 genetic polymorphisms with RA susceptibility were investigated.

RESULTS

A VPAC1 agonist was very efficient in the treatment of experimental arthritis, and deficient expression of VPAC1 in immune cells of RA patients was associated with the predominant proinflammatory Th1 milieu found in this disease. Immune cells derived from RA patients were less responsive to VIP signaling than were cells from healthy individuals and showed reduced VIP-mediated immunosuppressive activity, rendering leukocytes and synovial cells more proinflammatory in RA. A significant association between multiple-marker haplotypes of VPAC1 and susceptibility to RA was found, suggesting that the reduced VPAC1 expression in RA-derived immune cells is associated with the described VPAC1 genetic polymorphism.

CONCLUSION

These findings are highly relevant to the understanding of RA pathogenesis. They suggest that VIP signaling through VPAC1 is critical to maintaining immune tolerance in RA. In addition, the results indicate that VPAC1 may be a novel therapeutic target in RA.

Emerging roles of vasoactive intestinal peptide: a new approach for autoimmune therapy

Identification of the factors that regulate the immune tolerance and control the appearance of exacerbated inflammatory conditions is crucial for the development of new therapies of autoimmune diseases. Some neuropeptides and hormones have emerged as endogenous agents that participate in the regulation of the processes that ensure self-tolerance. Among them, the vasoactive intestinal peptide (VIP), a well-characterised endogenous anti-inflammatory neuropeptide, has shown therapeutic potential for a variety of immune disorders. Here we examine the latest research findings, which indicate that VIP participates in maintaining immune tolerance in two distinct ways: by regulating the balance between pro-inflammatory and anti-inflammatory factors, and by inducing the emergence of regulatory T cells with suppressive activity against autoreactive T cell effectors.

Tuning immune tolerance with vasoactive intestinal peptide: a new therapeutic approach for immune disorders

The induction of immune tolerance is essential for the maintenance of immune homeostasis and to limit the occurrence of exacerbated inflammatory and autoimmune conditions. Multiple mechanisms act together to ensure self-tolerance, including central clonal deletion, cytokine deviation and induction of regulatory T cells. Identifying the factors that regulate these processes is crucial for the development of new therapies of autoimmune diseases and transplantation. The vasoactive intestinal peptide (VIP) is a well-characterized endogenous anti-inflammatory neuropeptide with therapeutic potential for a variety of immune disorders. Here, we examine the latest research findings, which indicate that VIP participates in maintaining immune tolerance in two distinct ways: by regulating the balance between pro-inflammatory and anti-inflammatory factors, and by inducing the emergence of regulatory T cells with suppressive activity against autoreactive T-cell effectors.

Regulation of immune tolerance by anti-inflammatory neuropeptides

The induction of antigen-specific tolerance is essential to maintain immune homeostasis, control autoreactive T cells, prevent the onset of autoimmune diseases and achieve tolerance of transplants. Inflammation is a necessary process for eliminating pathogens, but can lead to serious deleterious effects in the host if left unchecked. Identifying the endogenous factors that control immune tolerance and inflammation is a key goal in the field of immunology. In the last decade, various neuropeptides that are produced by immune cells with potent anti-inflammatory actions were found to participate in the maintenance of tolerance in different immunological disorders.

Theory of proteolytic antibody occurrence

Antibodies (Abs) with proteolytic and other catalytic activities have been characterized in the blood and mucosal secretions of humans and experimental animals. The catalytic activity can be traced to nucleophilic sites of innate origin located in Ab germline variable regions. Discoveries of the natural chemical reactivity of Abs were initially met with bewilderment, as the notion had taken hold that catalytic activities can be introduced into Abs by artificial means, but somatically operative selection pressures are designed only to adapt non-covalent Ab binding to antigen ground states. Unsurprisingly, initial efforts to engineer Abs with catalytic activity were oriented towards improving the non-covalent binding at the atoms immediately within the transition state reaction center. Slowly, however, dogmatic approaches to Ab catalysis have given way to the realization that efficient and specific catalytic Abs can be prepared by improving the natural nucleophilic reactivity combined with non-covalent recognition of epitope regions remote from the reaction center. The field remains beset, however, with controversy. This article attempts to provide a rational basis for natural Ab catalysis, in the hope that understanding this phenomenon will stimulate medical and basic science advances in the field.

Vasoactive intestinal peptide induces regulatory dendritic cells with therapeutic effects on autoimmune disorders

The induction of antigen-specific tolerance is critical for the prevention of autoimmunity and maintenance of immune tolerance. In addition to their classical role as sentinels of the immune response-inducing T cell reactivity, dendritic cells (DCs) play an important role in maintaining peripheral tolerance through the induction/activation of regulatory T cells (Tr). The possibility to generate tolerogenic DCs opens new therapeutic perspectives in autoimmune/inflammatory diseases. Therefore, the characterization of the endogenous factors that contribute to the development of tolerogenic DCs is highly relevant. In this study, we report on the use of the known immunosuppressive neuropeptide, the vasoactive intestinal peptide, as a new approach to induce tolerogenic DCs with capacity to generate Tr cells, to restore tolerance in vivo, and to reduce the progression of rheumatoid arthritis and experimental autoimmune encephalomyelitis.

Antibodies as defensive enzymes

Antibodies (Abs) and enzymes are structural and functional relatives. Abs with promiscuous peptidase activity are ubiquitous in healthy humans, evidently derived from germline variable domain immunoglobulin genes encoding the serine protease-like nucleophilic function. Exogenous and endogenous electrophilic antigens can bind the nucleophilic sites covalently, and recent evidence suggests that immunization with such antigens can induce proteolytic antibodies. Previously, Ab catalytic activities have been linked to pathogenic autoimmune reactions, but recent studies indicate that proteolytic Abs may also serve beneficial functions. An example is the rapid and selective cleavage of the HIV-1 coat protein gp120 by IgMs found in uninfected humans. The selectivity of this reaction appears to derive from recognition of gp120 as a superantigen. A second example is the cleavage of amyloid beta-peptide by IgM and IgG from aged humans, a phenomenon that may represent a specific proteolytic response to a neurotoxic endogenous peptide implicated in the pathogenesis of Alzheimer's disease.

The many faces of VIP in neuroimmunology: a cytokine rather a neuropeptide?

Neuroimmunomodulation has experienced an explosive growth not only in basic research, but expanding to the point that prospective clinical research could be now a reality. A crucial factor for the functioning of this intimate bidirectional network was the demonstration that the immune and neuroendocrine systems speak a mutual biochemical language. This implies 1) production of neuroendocrine hormones and neuropeptides by immune cells and of cytokines by neuroendocrine cells; 2) evidence for shared receptors on cells of the immune and neuroendocrine systems; 3) effect of neuroendocrine mediators on immune functions; and 4) effect of cytokines on the neuroendocrine system. This reduces traditional differences between neurotransmitters, hormones, and immune mediators and raises the following question: what can we now regard as immune or neuroendocrine? Vasoactive intestinal peptide (VIP) is one example of this paradigm. VIP has traditionally been classified as a neuropeptide/neurotransmitter based in its capacity to mediate and regulate neuronal functions. Recent work has demonstrated that VIP is produced by T cells, especially Th2 cells, and that through specific receptors it exerts immunological functions typically ascribed to Th2 cytokines in nervous and immune systems. Here, we postulate that instead of a neuropeptide, VIP could be fully considered a type 2 cytokine with a key role in neuroimmunology.

Antibody light chain-catalyzed hydrolysis of a hepatitis C virus peptide

A panel of human monoclonal and recombinant antibody light chains was screened for cleavage of the synthetic peptide corresponding to a neutralizing epitope of hepatitis C virus (residues 192-205 of envelope glycoprotein E1). One of the 39 light chains studied hydrolyzed the Val197-Ser198 bond of the peptide with Km and kcat values of 223 +/- 7 microM and 0.087 +/- 0.001 min(-1).

Ontogeny of Proteolytic Immunity

We report the chemical activity of immunoglobulin micro and kappa/lambda subunits expressed on the surface of B cells and in secreted IgM antibodies (Abs) found in the preimmune repertoire. Most of the nucleophilic reactivity of B cells measured by formation of covalent adducts of a hapten amidino phosphonate diester was attributed to micro and kappa/lambda subunits of the B cell receptor. Secreted IgM Abs displayed superior nucleophilic reactivity than IgG Abs. IgM Abs catalyzed the cleavage of model peptide substrates at rates up to 344-fold greater than IgG Abs. Catalytic activities were observed in polyclonal IgM Abs from immunologically naïve mice and humans without immunological disease, as well as monoclonal IgM Abs to unrelated antigens. Comparison of several IgM Abs indicated divergent activity levels and substrate preferences, with the common requirement of a basic residue flanking the cleavage site. Fab fragments of a monoclonal IgM Ab expressed catalytic activity, confirming the V domain location of the catalytic site. The catalytic reaction was inhibited by the covalently reactive hapten probe and diisopropylfluorophosphate, suggesting a serine protease-like mechanism. These observations indicate the existence of serine protease-like BCRs and secreted IgM Abs as innate immunity components with potential roles in B cell development and Ab effector functions.

Toward selective covalent inactivation of pathogenic antibodies: a phosphate diester analog of vasoactive intestinal peptide that inactivates catalytic autoantibodies

We report the selective inactivation of proteolytic antibodies (Abs) to an autoantigen, the neuropeptide vasoactive intestinal peptide (VIP), by a covalently reactive analog (CRA) of VIP containing an electrophilic phosphonate diester at the Lys(20) residue. The VIP-CRA was bound irreversibly by a monoclonal Ab that catalyzes the hydrolysis of VIP. The reaction with the VIP-CRA proceeded more rapidly than with a hapten CRA devoid of the VIP sequence. The covalent binding occurred preferentially at the light chain subunit of the Ab. Covalent VIP-CRA binding was inhibited by VIP devoid of the phosphonate diester group. These results indicate the importance of noncovalent VIP recognition in guiding Ab nucleophilic attack on the phosphonate group. Consistent with the covalent binding data, the VIP-CRA inhibited catalysis by the recombinant light chain of this Ab with potency greater than the hapten-CRA. Catalytic hydrolysis of VIP by a polyclonal VIPase autoantibody preparation that cleaves multiple peptide bonds located between residues 7 and 22 essentially was inhibited completely by the VIP-CRA, suggesting that the electrophilic phosphonate at Lys(20) enjoys sufficient conformational freedom to react covalently with Abs that cleave different peptide bonds in VIP. These results suggest a novel route to antigen-specific covalent targeting of pathogenic Abs.

Specific HIV gp120-cleaving antibodies induced by covalently reactive analog of gp120

We report the results of efforts to strengthen and direct the natural nucleophilic activity of antibodies (Abs) for the purpose of specific cleavage of the human immunodeficiency virus-1 coat protein gp120. Phosphonate diester groups previously reported to form a covalent bond with the active site nucleophile of serine proteases (Paul, S., Tramontano, A., Gololobov, G., Zhou, Y. X., Taguchi, H., Karle, S., Nishiyama, Y., Planque, S., and George, S. (2001) J. Biol. Chem. 276, 28314-28320) were placed on Lys side chains of gp120. Seven monoclonal Abs raised by immunization with the covalently reactive analog of gp120 displayed irreversible binding to this compound (binding resistant to dissociation with the denaturant SDS). Catalytic cleavage of biotinylated gp120 by three monoclonal antibodies was observed. No cleavage of albumin and the extracellular domain of the epidermal growth factor receptor was detected. Cleavage of model peptide substrates occurred on the C-terminal side of basic amino acids, and Km for this reaction was approximately 200-fold greater than that for gp120 cleavage, indicating Ab specialization for the gp120 substrate. A hapten phosphonate diester devoid of gp120 inhibited the catalytic activity with exceptional potency, confirming that the reaction proceeds via a serine protease mechanism. Irreversible binding of the hapten phosphonate diester by polyclonal IgG from mice immunized with gp120 covalently reactive analog was increased compared with similar preparations from animals immunized with control gp120, indicating induction of Ab nucleophilicity. These findings suggest the feasibility of raising antigen-specific proteolytic antibodies on demand by covalent immunization.