On the mechanism of staphylococcal protein A immunomodulation

IgG hexamers initiate acute lung injury

Antibodies can initiate lung injury in a variety of disease states such as autoimmunity, transfusion reactions, or after organ transplantation, but the key factors determining in vivo pathogenicity of injury-inducing antibodies are unclear. A previously overlooked step in complement activation by IgG antibodies has been elucidated involving interactions between IgG Fc domains that enable assembly of IgG hexamers, which can optimally activate the complement cascade. Here, we tested the in vivo relevance of IgG hexamers in a complement-dependent alloantibody model of acute lung injury. We used three approaches to block alloantibody hexamerization (antibody carbamylation, the K439E Fc mutation, or treatment with domain B from Staphylococcal protein A), all of which reduced acute lung injury. Conversely, Fc mutations promoting spontaneous hexamerization made a harmful alloantibody into a more potent inducer of acute lung injury and rendered an innocuous alloantibody pathogenic. Treatment with a recombinant Fc hexamer 'decoy' therapeutic protected mice from lung injury, including in a model with transgenic human FCGR2A expression that exacerbated pathology. These results indicate a direct in vivo role of IgG hexamerization in initiating acute lung injury and the potential for therapeutics that inhibit or mimic hexamerization to treat antibody-mediated diseases.

Staphylococcusaureus protein A as a means of assessing sperm penetrability in cervical mucus in vitro

OBJECTIVE

The effectiveness of Staphylococcus protein A (SPA) in improving the penetration ability of sperm and reducing antisperm antibody (ASA) titers in immunologically infertile males was evaluated.

METHODS

Seminal fluid samples were obtained from 15 infertile men, and ASA titers were assessed with the latex agglutination test. Identification of immunoglobulin (Ig) classes and characterization of the antigens involved in the immune response were performed using indirect immunofluorescence. Local ASAs typically present as a mixture of IgG and IgA classes. The capillary tube penetration method was used to assess the capability of spermatozoa to penetrate the cervical mucus (CM).

RESULTS

ASAs associated with the neck region of sperm showed a significantly lower migration distance in the CM of infertile females than ASAs associated with the head or tail segments. ASA-positive seminal fluid exhibited significant increases in the mean migration distance (2.6 ± 1.4 cm vs. 1.54 ± 1.1 cm, respectively; p< 0.001) and sperm concentration (174 ± 121.0 × 10³/mL vs. 101 ± 93.7 × 10³/mL, respectively; p= 0.033) after treatment with SPA compared to pre-treated samples. A significant reduction (p< 0.01) in the recorded ASA titer was detected.

CONCLUSION

These results indicate that SPA can be used as a sorting regimen for insemination programs. However, further studies are warranted to assess its influence on pregnancy rate.

Homogenous Scavenging Resolves Low-Purification Yield/Selectivity Caused by Secondary Binding of Protein-A to Antigen-Binding Antibody Fragments

Antigen-binding fragments of antibodies are biotechnologically useful agents for decorating drug delivery systems, for blocking cell-surface receptors in cell culture, for recognizing analytes in biosensors, and potentially as therapeutics. They are typically produced by enzymatic digestion of full antibodies and isolated from the undesirable fragment crystallizable (Fc) by affinity chromatography using Protein-A columns. However, while Protein-A has a strong "classical" interaction with Fc fragments, it can also more weakly bind to an "alternative" site on the heavy chain variable region of antigen-binding fragments. As such, purifying small amounts of antibody fragments by Protein-A chromatography can result in low yield. Moreover, loading larger amounts of antibody fragments onto a Protein-A column can result in poor separation, because of competition of Fc and antigen-binding fragments for immobilized Protein-A. This study demonstrates that Protein-A-based homogeneous scavenging resolves this issue by precisely controlling the stoichiometry of Protein-A to Fc fragments, something that is not possible for conventional flow-type systems, such as affinity chromatography.

Guidelines on the Use of Therapeutic Apheresis in Clinical Practice - Evidence-Based Approach from the Writing Committee of the American Society for Apheresis: The Eighth Special Issue

The American Society for Apheresis (ASFA) Journal of Clinical Apheresis (JCA) Special Issue Writing Committee is charged with reviewing, updating and categorizing indications for the evidence-based use of therapeutic apheresis (TA) in human disease. Since the 2007 JCA Special Issue (Fourth Edition), the committee has incorporated systematic review and evidence-based approaches in the grading and categorization of apheresis indications. This Eighth Edition of the JCA Special Issue continues to maintain this methodology and rigor in order to make recommendations on the use of apheresis in a wide variety of diseases/conditions. The JCA Eighth Edition, like its predecessor, continues to apply the category and grading system definitions in fact sheets. The general layout and concept of a fact sheet that was introduced in the Fourth Edition, has largely been maintained in this edition. Each fact sheet succinctly summarizes the evidence for the use of TA in a specific disease entity or medical condition. The Eighth Edition comprises 84 fact sheets for relevant diseases and medical conditions, with 157 graded and categorized indications and/or TA modalities. The Eighth Edition of the JCA Special Issue seeks to continue to serve as a key resource that guides the utilization of TA in the treatment of human disease.

Nanobodies: Chemical Functionalization Strategies and Intracellular Applications

Nanobodies can be seen as next-generation tools for the recognition and modulation of antigens that are inaccessible to conventional antibodies. Due to their compact structure and high stability, nanobodies see frequent usage in basic research, and their chemical functionalization opens the way towards promising diagnostic and therapeutic applications. In this Review, central aspects of nanobody functionalization are presented, together with selected applications. While early conjugation strategies relied on the random modification of natural amino acids, more recent studies have focused on the site-specific attachment of functional moieties. Such techniques include chemoenzymatic approaches, expressed protein ligation, and amber suppression in combination with bioorthogonal modification strategies. Recent applications range from sophisticated imaging and mass spectrometry to the delivery of nanobodies into living cells for the visualization and manipulation of intracellular antigens.

Novel Evasion Mechanisms of the Classical Complement Pathway

Complement is a network of soluble and cell surface-associated proteins that gives rise to a self-amplifying, yet tightly regulated system with fundamental roles in immune surveillance and clearance. Complement becomes activated on the surface of nonself cells by one of three initiating mechanisms known as the classical, lectin, and alternative pathways. Evasion of complement function is a hallmark of invasive pathogens and hematophagous organisms. Although many complement-inhibition strategies hinge on hijacking activities of endogenous complement regulatory proteins, an increasing number of uniquely evolved evasion molecules have been discovered over the past decade. In this review, we focus on several recent investigations that revealed mechanistically distinct inhibitors of the classical pathway. Because the classical pathway is an important and specific mediator of various autoimmune and inflammatory disorders, in-depth knowledge of novel evasion mechanisms could direct future development of therapeutic anti-inflammatory molecules.

Guidelines on the Use of Therapeutic Apheresis in Clinical Practice-Evidence-Based Approach from the Writing Committee of the American Society for Apheresis: The Seventh Special Issue

The American Society for Apheresis (ASFA) Journal of Clinical Apheresis (JCA) Special Issue Writing Committee is charged with reviewing, updating, and categorizing indications for the evidence-based use of therapeutic apheresis in human disease. Since the 2007 JCA Special Issue (Fourth Edition), the Committee has incorporated systematic review and evidence-based approaches in the grading and categorization of apheresis indications. This Seventh Edition of the JCA Special Issue continues to maintain this methodology and rigor to make recommendations on the use of apheresis in a wide variety of diseases/conditions. The JCA Seventh Edition, like its predecessor, has consistently applied the category and grading system definitions in the fact sheets. The general layout and concept of a fact sheet that was used since the fourth edition has largely been maintained in this edition. Each fact sheet succinctly summarizes the evidence for the use of therapeutic apheresis in a specific disease entity. The Seventh Edition discusses 87 fact sheets (14 new fact sheets since the Sixth Edition) for therapeutic apheresis diseases and medical conditions, with 179 indications, which are separately graded and categorized within the listed fact sheets. Several diseases that are Category IV which have been described in detail in previous editions and do not have significant new evidence since the last publication are summarized in a separate table. The Seventh Edition of the JCA Special Issue serves as a key resource that guides the utilization of therapeutic apheresis in the treatment of human disease. J. Clin. Apheresis 31:149-162, 2016. © 2016 Wiley Periodicals, Inc.

Therapeutic Apheresis in Hematologic, Autoimmune and Dermatologic Diseases With Immunologic Origin

The process of curing a patient by removing his illness by extracting blood is a very old one. Many years ago, phlebotomy was practiced to cure illness. Now, this old process, placed on a rational basis with therapeutic apheresis (TA), is being followed in clinical practice. Therapeutic plasma exchange (TPE) with hollow fiber modules has been used in different severe diseases for more than 40 years. Based on many years of experience with the extracorporeal circulation in end-stage renal disease, the authors herein give an overview of TA in immunological diseases, especially in hematologic, autoimmune and dermatologic diseases. Updated information on immunology and molecular biology of different immunological diseases is discussed in relation to the rationale for apheresis therapy and its place in combination with other modern therapies. With the introduction of novel and effective biologic agents, TA is indicated only in severe cases, such as in rapid progression despite immunosuppressive therapy and/or biologic agents. In mild forms of autoimmune disease, treatment with immunosuppressive therapies and/or biologic agents seems to be sufficient. The prognosis of autoimmune diseases with varying organ manifestations has improved in recent years, due in part to very aggressive therapy schemes. For the immunological diseases that can be treated with TA, the guidelines of the German Working Group of Clinical Nephrology and of the Apheresis Applications Committee of the American Society for Apheresis are cited. TA has been shown to effectively remove the autoantibodies from blood and lead to rapid clinical improvement.

PRTX-100 and methotrexate in patients with active rheumatoid arthritis: A Phase Ib randomized, double-blind, placebo-controlled, dose-escalation study

PRTX-100 is a highly-purified preparation of staphylococcal protein A (SpA), with immunologic activity in vitro and in animal models of immune-mediated inflammation. Following single-dose healthy volunteer studies of safety and pharmacokinetics (PK), a multicenter, double-blind, placebo-controlled, sequential dose-escalation, repeated-dose phase I trial was conducted in patients with active rheumatoid arthritis (RA) on methotrexate therapy. Patients were randomized to receive either weekly intravenous PRTX-100 (0.15, 0.45, 0.90, or 1.50 µg/kg) or placebo for 4 weeks. Safety and disease activity were assessed over 16 weeks. Pharmacokinetic profiles were obtained after the first and fourth doses. The most common treatment-related adverse events were nausea, muscle spasms, dizziness, flushing, fatigue, RA flare, and headache. No serious adverse events were considered related to PRTX-100, and none occurred in the highest dose group. Geometric mean values for plasma Cmax (ng/mL) were 4.1, 15.7, 26.5, and 51.2 for doses of 0.15, 0.45, 0.90, and 1.5 µg/kg, respectively. Anti-drug antibodies (ADAs) developed in most PRTX-100 patients, but incidence and titer were not dose-dependent. At the two highest doses, data suggest PRTX-100 may have an effect on RA disease activity, even in patients with ADAs.

Studies of the safety, pharmacokinetics and immunogenicity of repeated doses of intravenous staphylococcal protein A in cynomolgus monkeys

Three Good Laboratory Practice safety studies were performed with intravenous injections of highly purified staphylococcal protein A (SPA) in cynomolgus monkeys, in support of a clinical development programme utilizing this protein as an immunomodulator. These studies established a no-observable-adverse-effect level (NOAEL) for up to 12 weekly doses of SPA, as well as toxicokinetic profiles for SPA, evaluation of antiproduct antibodies and biomarkers to better characterize the pharmacodynamic response to SPA. Biomarkers included neopterin, C-reactive protein (CRP), troponin I and the change in the blood absolute lymphocyte count (ALC) 24 hr after SPA dosing. The transient decrease in ALC noted at 24 hr after dosing was similar to that seen in human Phase 1 trials. The majority of active-treated monkeys developed antibodies against SPA. Cmax was not affected by development of antidrug antibodies (ADAs), and after the first dose was 87 (SD 19) ng/mL, 330 (SD 84) ng/mL and 1191 (SD 208) ng/mL for 5, 25 and 100 μg/kg doses, respectively. The development of ADAs increased plasma clearance of SPA. By the sixth weekly dose, the AUC was decreased by 76%, 54% and 66% for the 5, 25 and 100 μg/kg dose groups, respectively. These results indicate that SPA can be administered intravenously to non-human primates without observable toxicity at weekly doses of up to 100 μg/kg.

Co-opting endogenous immunoglobulin for the regulation of inflammation and osteoclastogenesis in humans and mice

OBJECTIVE

Cells of the monocytic lineage play fundamental roles in the regulation of health, ranging from the initiation and resolution of inflammation to bone homeostasis. In rheumatoid arthritis (RA), the inflamed synovium exhibits characteristic infiltration of macrophages along with local osteoclast maturation, which, together, drive chronic inflammation and downstream articular destruction. The aim of this study was to explore an entirely novel route of immunoglobulin-mediated regulation, involving simultaneous suppression of the inflammatory and erosive processes in the synovium.

METHODS

Using in vivo and in vitro studies of human cells and a murine model of RA, the ability of staphylococcal protein A (SPA) to interact with and modulate cells of the monocytic lineage was tested. In addition, the efficacy of SPA as a therapeutic agent was evaluated in murine collagen-induced arthritis (CIA).

RESULTS

SPA showed a capacity to appropriate circulating IgG, by generating small immunoglobulin complexes that interacted with monocytes, macrophages, and preosteoclasts. Formation of these complexes resulted in Fcγ receptor type I-dependent polarization of macrophages to a regulatory phenotype, rendering them unresponsive to activators such as interferon-γ. The antiinflammatory complexes also had the capacity to directly inhibit differentiation of preosteoclasts into osteoclasts in humans. Moreover, administration of SPA in the early stages of disease substantially alleviated the clinical and histologic erosive features of CIA in mice.

CONCLUSION

These findings demonstrate the overarching utility of immunoglobulin complexes for the prevention and treatment of inflammatory diseases. The results shed light on the interface between immunoglobulin complex-mediated pathways, osteoclastogenesis, and associated pathologic processes. Thus, therapeutic agents designed to harness all of these properties may be an effective treatment for arthritis, by targeting both the innate inflammatory response and prodestructive pathways.

2,4,6-trisubstituted triazines as protein a mimetics for the treatment of autoimmune diseases

A first-in-class series of low molecular weight trisubstituted triazines were synthesized and evaluated for their ability to mimic protein A binding to human IgG antibody. The structure-activity relationship (SAR) demonstrates that the 1,3-phenylenediamine component was essential for robust activity. Twenty-two compounds, represented by lead molecule 34, displayed significant activity compared to protein A. These compounds may prove useful for the treatment of autoimmune disease.

Complement and its role in innate and adaptive immune responses

The complement system plays a crucial role in the innate defense against common pathogens. Activation of complement leads to robust and efficient proteolytic cascades, which terminate in opsonization and lysis of the pathogen as well as in the generation of the classical inflammatory response through the production of potent proinflammatory molecules. More recently, however, the role of complement in the immune response has been expanded due to observations that link complement activation to adaptive immune responses. It is now appreciated that complement is a functional bridge between innate and adaptive immune responses that allows an integrated host defense to pathogenic challenges. As such, a study of its functions allows insight into the molecular underpinnings of host-pathogen interactions as well as the organization and orchestration of the host immune response. This review attempts to summarize the roles that complement plays in both innate and adaptive immune responses and the consequences of these interactions on host defense.

Immune evasion of Enterococcus faecalis by an extracellular gelatinase that cleaves C3 and iC3b

Enterococcus faecalis (Ef) accounts for most cases of enterococcal bacteremia, which is one of the principal causes of nosocomial bloodstream infections (BSI). Among several virulence factors associated with the pathogenesis of Ef, an extracellular gelatinase (GelE) has been known to be the most common factor, although its virulence mechanisms, especially in association with human BSI, have yet to be demonstrated. In this study, we describe the complement resistance mechanism of Ef mediated by GelE. Using purified GelE, we determined that it cleaved the C3 occurring in human serum into a C3b-like molecule, which was inactivated rapidly via reaction with water. This C3 convertase-like activity of GelE was shown to result in a consumption of C3 and thus inhibited the activation of the complement system. Also, GelE was confirmed to degrade an iC3b that was deposited on the Ag surfaces without affecting the bound C3b. This proteolytic effect of GelE against the major complement opsonin resulted in a substantial reduction in Ef phagocytosis by human polymorphonuclear leukocytes. In addition, we verified that the action of GelE against C3, which is a central component of the complement cascade, was human specific. Taken together, it was suggested that GelE may represent a promising molecule for targeting human BSI associated with Ef.

Bacterial complement escape

Complement activation is a crucial step in our innate immune defense against invading bacteria. Complement proteins can quickly recognize invading bacteria and subsequently label them for phagocytosis or kill them by direct lysis. In order to survive in the human host, bacterial pathogens have evolved a number of excreted and membrane-bound proteins that interfere with several steps of the complement cascade. In this chapter we summarize the most successful complement-modulating strategies by human bacterial pathogens.

2,6,9-Trisubstituted purine derivatives as protein A mimetics for the treatment of autoimmune diseases

A series of 9-substituted and 2,9-disubstituted 6-(3-aminophenylamino) purines were synthesized and evaluated for their ability to mimic protein A binding to human IgG antibody. The structure-activity relationship (SAR) demonstrates that the 6-(3-aminoanilinyl) purine component was essential for activity. Purine 14 demonstrated significant activity, compared to protein A. These compounds may prove useful for the treatment of autoimmune diseases.

Interaction of human complement with Sbi, a staphylococcal immunoglobulin-binding protein: indications of a novel mechanism of complement evasion by Staphylococcus aureus

Staphylococcal immunoglobulin-binding protein, Sbi, is a 436-residue protein produced by many strains of Staphylococcus aureus. It was previously characterized as being cell surface-associated and having binding capacity for human IgG and beta(2)-glycoprotein I. Here we show using small angle x-ray scattering that the proposed extracellular region of Sbi (Sbi-E) is an elongated molecule consisting of four globular domains, two immunoglobulin-binding domains (I and II) and two novel domains (III and IV). We further show that together domains III and IV (Sbi-III-IV), as well as domain IV on its own (Sbi-IV), bind complement component C3 via contacts involving both the C3dg fragment and the C3a anaphylatoxin domain. Preincubation of human serum with either Sbi-E or Sbi-III-IV is inhibitory to all complement pathways, whereas domain IV specifically inhibits the alternative pathway. Monitoring C3 activation in serum incubated with Sbi fragments reveals that Sbi-E and Sbi-III-IV both activate the alternative pathway, leading to consumption of C3. By contrast, inhibition of this pathway by Sbi-IV does not involve C3 consumption. The observation that Sbi-E activates the alternative pathway is counterintuitive to intact Sbi being cell wall-associated, as recruiting complement to the surface of S. aureus would be deleterious to the bacterium. Upon re-examination of this issue, we found that Sbi was not associated with the cell wall fraction, but rather was found in the growth medium, consistent with it being an excreted protein. As such, our data suggest that Sbi helps mediate bacterial evasion of complement via a novel mechanism, namely futile fluid-phase consumption.

S. aureus IgG-binding proteins SpA and Sbi: host specificity and mechanisms of immune complex formation

The evasion of the host immune response is central to the pathogenicity of Staphylococcus aureus, and is facilitated by the ability of the cell wall-associated protein A (SpA) to bind immunoglobulin G Fc fragments, thereby impeding phacocytosis and classical pathway complement fixation. SpA also acts as a B-cell superantigen through interactions with the heavy-chain variable part of Fab fragments, and sequesters immunoglobulins by forming large insoluble immune complexes with human IgG. Here we show that the formation of insoluble immune complexes is mediated by the binding of (VH3+) Fab fragments in addition to Fc, and that SpA forms soluble complexes with IgG Fc fragments. We compared these results with those for Sbi, a second staphylococcal immunoglobulin-binding protein, and note that this protein requires only the Fc fragment for precipitation with human IgG. Homology models of immunoglobulin-binding domains of SpA and Sbi in complex with Fc reveal the molecular basis of the Fab-independent formation of insoluble complexes by Sbi. Finally, we compared the sequences of the spa and sbi genes from human strains to those infecting a range of animal hosts to determine whether Sbi and SpA have acquired specificity for host IgG. We note remarkable sequence conservation within the IgG-binding domains of these genes, consistent with a lack of host specificity. The Fab-independent binding of IgG by Sbi could have significant clinical implications. The use of SpA in immunoadsorption therapy can cause severe side-effects, thought to be mediated by Fc gamma R recognition and complement fixation. The formation of insoluble immune complexes with Sbi occurs only via Fc binding and free Fc regions are unlikely to be available for Fc gamma R recognition and complement fixation.

Isolation of pathogenic monoclonal anti-desmoglein 1 human antibodies by phage display of pemphigus foliaceus autoantibodies

Pemphigus foliaceus (PF) is a blistering disease caused by autoantibodies to desmoglein 1 (Dsg1) that cause loss of epidermal cell adhesion. To better understand PF pathophysiology, we used phage display to isolate anti-Dsg1 mAbs as single-chain variable fragments (scFvs) from a PF patient. Initial panning of the library isolated only non-pathogenic scFvs. We then used these scFvs to block non-pathogenic epitopes and were able to isolate two unique scFvs, each of which caused typical PF blisters in mice or human epidermis models, showing that a single mAb can disrupt Dsg1 function to cause disease. Both pathogenic scFvs bound conformational epitopes in the N terminus of Dsg1. Other PF sera showed a major antibody response against the same or nearby epitopes defined by these pathogenic scFvs. Finally, we showed restriction of the heavy-chain gene usage of all anti-Dsg1 clones to only five genes, which determined their immunological properties despite promiscuous light-chain gene usage. These mAbs will be useful for studying Dsg1 function and mechanisms of blister formation in PF and for developing targeted therapies and tools to monitor disease activity.

B cell modulation in rheumatology

While evidence of dysregulation of the B cell compartment was first demonstrated with the identification of autoantibodies, other functional roles of B lymphocytes in autoimmune pathogenesis have generally been underappreciated or completely overlooked. With the recent approval of the first B cell targeting agent in rheumatoid arthritis, new strategies are being developed to target B cells through a range of membrane-associated lineage-specific molecules and also by interfering with B-cell-specific pro-survival signals. B-cell-directed agents therefore provide an effective new mechanistic approach to treatment and also enable new perspectives from the dissection of the contributions of B cells in physiologic and pathologic immune responses.

Future of antibody purification

Antibody purification seems to be safely ensconced in a platform, now well-established by way of multiple commercialized antibody processes. However, natural evolution compels us to peer into the future. This is driven not only by a large, projected increase in the number of antibody therapies, but also by dramatic improvements in upstream productivity, and process economics. Although disruptive technologies have yet escaped downstream processes, evolution of the so-called platform is already evident in antibody processes in late-stage development. Here we perform a wide survey of technologies that are competing to be part of that platform, and provide our [inherently dangerous] assessment of those that have the most promise.

Guidelines on the use of therapeutic apheresis in clinical practice—Evidence-based approach from the apheresis applications committee of the American society for apheresis

The American Society for Apheresis (ASFA) Apheresis Applications Committee is charged with a review and categorization of indications for therapeutic apheresis. This elaborate process had been undertaken every 7 years resulting in three prior publications in 1986, 1993, and 2000 of "The ASFA Special Issues." This article is the integral part of the Fourth ASFA Special Issue. The Fourth ASFA Special Issue is significantly modified in comparison to the previous editions. A new concept of a fact sheet has been introduced. The fact sheet succinctly summarizes the evidence for the use of therapeutic apheresis. A detailed description of the fact sheet is provided. The article consists of 53 fact sheets devoted to each disease entity currently categorized by the ASFA. Categories I, II, and III are defined as previously in the Third Special Issue. However, a few new therapeutic apheresis modalities, not yet approved in the United States or are currently in clinical trials, have been assigned category P (pending) by the ASFA Clinical Categories Subcommittee. The diseases assigned to category IV are discussed in a separate article in this issue.

Decreased immune reactivity towards a knobless, affibody-targeted adenovirus type 5 vector

In this study, a prototype Adenovirus type 5 (Ad5) vector deleted of the fiber knob domain and carrying an Affibody molecule as the targeting ligand showed decreased susceptibility to human pre-existing antibodies. This vector, Ad5/R7-Z(taq)Z(taq), has short fibers carrying seven shaft repeats, a non-native trimerization signal and an affibody molecule (Z(taq)) reactive to Taq polymerase. Ad5/R7-Z(taq)Z(taq) could be specifically targeted to 293 cells stably expressing membrane-bound anti-Z(taq) idiotypic affibody called Z(ztaq) (293Z(ztaq)). Sera from 50 blood donors were analyzed for neutralization activity (NA) against the parental Ad5/Fiwt vector and knobless Ad5/R7-Z(taq)Z(taq) on 293Z(ztaq) cells. Twenty-three sera had NA titers (> or =1:64) against Ad5/Fiwt (46%) and only two against Ad5/R7-Z(taq)Z(taq) (4%). Characterization of sera with NA titers showed that the knob domain is one of the targets of the antibodies. Neutralization assays using sera pre-adsorbed on knob and hexon proteins showed that the NA of the sera was carried mainly by anti-knob and anti-hexon antibodies, but in certain sera the anti-hexon antibodies represent the major population of the neutralizing antibodies (NAbs). Our results suggested that a combination of knob deletion and hexon switching could be an effective strategy for Ad vectors to better evade the anti-Ad NAbs.

Bacterial complement evasion

The human complement system is elemental to recognize bacteria, opsonize them for handling by phagocytes, or kill them by direct lysis. However, successful bacterial pathogens have in turn evolved ingenious strategies to overcome this part of the immune system. In this review we discuss the different stages of complement activation sequentially and illustrate the immune evasion strategies that various bacteria have developed to evade each subsequent step. The focus is on bacterial proteins, either surface-bound or excreted, that block complement activation. The underlying molecular mechanism of action and the possible role in pathophysiology of bacterial infections are discussed.

Confounding B-cell defences: lessons from a staphylococcal superantigen

Studies of microbial superantigens that target large clonal sets of B cells through conserved antigen-receptor-variable-region sites are providing new insights into the mechanisms of B-cell activation-induced cell death. These investigations have shown differences between the clonal regulation of follicular B cells (B2 cells) and the innate-like marginal-zone B cells and B1 cells, and have also shown how B-cell superantigens can affect specialized host defences against infection. Agents designed to emulate the properties of B-cell superantigens might also provide new approaches for the treatment of B-cell-mediated autoimmune and neoplastic diseases.

Presensitization: the problem and its management

Much attention has been placed recently on transplantation in highly HLA-sensitized patients. In attempts to remove these antibodies and enable successful transplantation, several novel approaches have been developed. These include intravenous Ig (IVIg), mycophenolate mofetil, sirolimus, alemtuzumab, protein A immunoabsorption, and rituximab. IVIg has emerged as a very effective agent when used alone in high dose or when used in low dose and combined with plasmapheresis. Although alemtuzumab has been used to eliminated B cells, it fails to prevent antibody-mediated rejection and therefore probably is not suitable for desensitization. Rituximab, a B cell-specific antibody, seems to be safe and to have some efficacy as a sole agent in elimination of alloantibodies but most likely will require combination therapy with IVIg or other agents. Newer agents, such as humanized anti-CD20, are being developed. Despite the great interest in the problem of allosensitization, with one notable exception, there is a major deficiency in controlled clinical trials, the conduct of which should be a focus for the near future.

Temporal and Dose-Dependent Relationships between In Vivo B Cell Receptor-Targeted Proliferation and Deletion-Induced by a Microbial B Cell Toxin

The effective functioning of the adaptive immune system requires careful clonal regulation within the B cell compartment. Some microbial pathogens produce virulence factors, like staphylococcal protein A, which interact at high frequencies with B lymphocyte through unconventional binding sites in BCR variable region frameworks conserved during evolution. We have characterized the in vivo effect of staphylococcal protein A treatment on peripheral B cells bearing susceptible BCR, and found a dose-dependent direct relationship over the range of 2 mg to <0.2 microg in the magnitude of induced BCR-targeted supraclonal cell death. Significantly, some level of targeted B cell proliferation was always detectable, with greatest interim supraclonal expansion demonstrated at 2 days after 20-microg treatment. Subsequently, this transient expansion always collapsed. In direct comparisons, i.p. treatment was more efficacious than i.v. treatment, although at higher doses this finding was less marked. These studies elucidate a general paradigm in which in vivo encounters with a B cell superantigen are uniformly associated with proliferative expansion followed by deletion that is more rapid and complete with higher doses, whereas lower doses lead to greater transient in vivo expansion with delayed deletion to levels at later times that are still quantitatively proportional to the dose. Our results document the potent in vivo B cell-targeted properties of a microbial B cell superantigen, even at submicrogram doses associated with great molar excess of circulating Ig, and clearly illustrate the intertwined relationships between targeted proliferative cycling and apoptotic death that is induced by a microbial B cell superantigen.

Genetic and functional characterization of human pemphigus vulgaris monoclonal autoantibodies isolated by phage display

Pemphigus is a life-threatening blistering disorder of the skin and mucous membranes caused by pathogenic autoantibodies to desmosomal adhesion proteins desmoglein 3 (Dsg3) and Dsg1. Mechanisms of antibody pathogenicity are difficult to characterize using polyclonal patient sera. Using antibody phage display, we have isolated repertoires of human anti-Dsg mAbs as single-chain variable-region fragments (scFvs) from a patient with active mucocutaneous pemphigus vulgaris. ScFv mAbs demonstrated binding to Dsg3 or Dsg1 alone, or both Dsg3 and Dsg1. Inhibition ELISA showed that the epitopes defined by these scFvs are blocked by autoantibodies from multiple pemphigus patients. Injection of scFvs into neonatal mice identified 2 pathogenic scFvs that caused blisters histologically similar to those observed in pemphigus patients. Similarly, these 2 scFvs, but not others, induced cell sheet dissociation of cultured human keratinocytes, indicating that both pathogenic and nonpathogenic antibodies were isolated. Genetic analysis of these mAbs showed restricted patterns of heavy and light chain gene usage, which were distinct for scFvs with different desmoglein-binding specificities. Detailed characterization of these pemphigus mAbs should lead to a better understanding of the immunopathogenesis of disease and to more specifically targeted therapeutic approaches.