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G J Silverman

Publications and source records attributed to G J Silverman.

At least 19 recordsLinked to original sources
PubMed2001

Adoptive transfer of a superantigen-induced hole in the repertoire of natural IgM-secreting cells.

We have recently evaluated the host response to the bacterial toxin, protein A from Staphylococcus aureus (SpA), which has the capacity to interact with B-cell antigen receptors encoded by V(H) clan III genes via a conserved variable region framework surface. In these studies, intraperitoneal instillation of SpA induced a persistent T-cell independent loss of a large supraclonal set of susceptible lymphocytes, which includes clan III/V(H) S107 family-expressing B-1 cells and their antibody products. To determine whether these long-term effects could represent the influence of residual in vivo deposited superantigen, we have now performed adoptive transfer of peritoneal B cells from superantigen- and control-treated donors. These studies demonstrated that mice that received cells from SpA-treated donors also exhibited the same induced supraclonal hole in the expressed repertoire of natural IgM-secreting cells due to supraclonal deletion. These studies clarify the cellular mechanisms responsible for B-cell superantigen-induced modification of the repertoires of in vivo polyclonal B-cell populations.

Adoptive Transfer↗
PubMed2001

Human-derived anti-oxidized LDL autoantibody blocks uptake of oxidized LDL by macrophages and localizes to atherosclerotic lesions in vivo.

Autoantibodies to oxidation-specific epitopes of low density lipoprotein (LDL), such as malondialdehyde-modified LDL (MDA-LDL), occur in plasma and atherosclerotic lesions of humans and animals. Plasma titers of such antibodies are correlated with atherosclerosis in murine models, and several such autoantibodies have been cloned. However, human-derived monoclonal antibodies to epitopes of oxidized LDL (OxLDL) have not yet been reported. We constructed a phage display antibody library from a patient with high plasma anti-MDA-LDL titers and isolated 3 monoclonal IgG Fab antibodies, which specifically bound to MDA-LDL. One of these, IK17, also bound to intact OxLDL as well as to its lipid and protein moieties but not to those of native LDL. IK17 inhibited the uptake of OxLDL by macrophages and also bound to apoptotic cells and inhibited their phagocytosis by macrophages. IK17 strongly immunostained necrotic cores of human and rabbit atherosclerotic lesions. When (125)I-IK17 was injected intravenously into LDL receptor-deficient mice, its specific uptake was greatly enriched in atherosclerotic plaques versus normal aortic tissue. Human autoantibodies to OxLDL have important biological properties that could influence the natural course of atherogenesis.

Animals↗
PubMed2001

Regulation of inherently autoreactive VH4-34 B cells in the maintenance of human B cell tolerance.

The study of human B cell tolerance has been hampered by difficulties in identifying a sizable population of autoreactive B lymphocytes whose fate could be readily determined. Hypothesizing that B cells expressing intrinsically autoreactive antibodies encoded by the VH4-34 heavy chain gene (VH4-34 cells) represent such a population, we tracked VH4-34 cells in healthy individuals. Here, we show that naive VH4-34 cells are positively selected and mostly restricted to the follicular mantle zone. Subsequently, these cells are largely excluded from the germinal centers and underrepresented in the memory compartment. In healthy donors but not in patients with systemic lupus erythematosus (SLE), these cells are prevented from differentiating into antibody-producing plasma cells. This blockade can be overcome ex vivo using cultures of naive and memory VH4-34 cells in the presence of CD70, IL-2, and IL-10. VH4-34 cells may therefore represent an experimentally useful surrogate for autoantibody transgenes and should prove valuable in studying human B cell tolerance in a physiological, polyclonal environment. Our initial results suggest that both positive and negative selection processes participate in the maintenance of tolerance in autoreactive human B cells at multiple checkpoints throughout B cell differentiation and that at least some censoring mechanisms are faulty in SLE.

B-Lymphocytes↗
PubMed2000

A B cell superantigen-induced persistent "Hole" in the B-1 repertoire.

The bacterial toxin protein A from Staphylococcus aureus (SpA) interacts with B cell antigen receptors encoded by variable region heavy chain (V(H)) clan III genes via a V region framework surface that has been highly conserved during the evolution of the adaptive immune system. We have investigated the consequences of exposure to this prototypic B cell superantigen, and found that treatment of neonates or adults induces a T cell-independent deletion of a large supraclonal set of susceptible B cells that includes clan III/V(H) S107 family-expressing lymphocytes. In studies of different SpA forms, the magnitude of the induced deletion directly correlated with the V(H)-specific binding affinity/avidity. Upon cessation of SpA exposure, the representation of conventional splenic (B-2 subset) lymphocytes normalized; however, we found that the V(H) family-restricted deficit of peritoneal B-1 cells persisted. SpA treatment also induced a persistent loss of splenic S107-mu transcripts, with a loss of certain natural antibodies and specific tolerance to phosphorylcholine immunogens that normally recruit protective antimicrobial responses dominated by the S107-expressing B-1 clone, T15. These studies illustrate how a B cell superantigen can exploit a primordial Achilles heel in the immune system, for which B-1 cells, an important source of natural antibodies and host immune responses, have special susceptibility.

Adult↗
PubMed2000

Crystal structure of a Staphylococcus aureus protein A domain complexed with the Fab fragment of a human IgM antibody: structural basis for recognition of B-cell receptors and superantigen activity.

Staphylococcus aureus produces a virulence factor, protein A (SpA), that contains five homologous Ig-binding domains. The interactions of SpA with the Fab region of membrane-anchored Igs can stimulate a large fraction of B cells, contributing to lymphocyte clonal selection. To understand the molecular basis for this activity, we have solved the crystal structure of the complex between domain D of SpA and the Fab fragment of a human IgM antibody to 2.7-A resolution. In the complex, helices II and III of domain D interact with the variable region of the Fab heavy chain (V(H)) through framework residues, without the involvement of the hypervariable regions implicated in antigen recognition. The contact residues are highly conserved in human V(H)3 antibodies but not in other families. The contact residues from domain D also are conserved among all SpA Ig-binding domains, suggesting that each could bind in a similar manner. Features of this interaction parallel those reported for staphylococcal enterotoxins that are superantigens for many T cells. The structural homology between Ig V(H) regions and the T-cell receptor V(beta) regions facilitates their comparison, and both types of interactions involve lymphocyte receptor surface remote from the antigen binding site. However, T-cell superantigens reportedly interact through hydrogen bonds with T-cell receptor V(beta) backbone atoms in a primary sequence-independent manner, whereas SpA relies on a sequence-restricted conformational binding with residue side chains, suggesting that this common bacterial pathogen has adopted distinct molecular recognition strategies for affecting large sets of B and T lymphocytes.

Amino Acid Sequence↗
PubMed2000

Characterization of superantigen-induced clonal deletion with a novel clan III-restricted avian monoclonal antibody: exploiting evolutionary distance to create antibodies specific for a conserved VH region surface.

Evolution of the Ab system has yielded three clans of VH region genes that are represented in almost every known higher species with an adaptive immune system. These clans are defined by sequence homologies primarily in highly conserved framework (FR) subdomains, which serve a scaffolding function maintaining the conformation of loops responsible for Ag binding. Structural analyses indicate that the VH FR1 and FR3 form a conserved composite exposed surface, which has been implicated in interactions with B cell superantigens. To directly investigate the expression of clan-defined supraclonal sets, we exploited the evolutionary distance of the chicken immune system and the selection power of phage display, to derive Abs diagnostic for clan III Ig. Using a specially tailored immunization and selection strategy, we created recombinant avian single chain Fv Abs specific for the clan III products, including those from the human VH3 family, and the analogous murine 7183, S107, J606, X24, and DNA4 families, and binding was competitive with natural B cell superantigens. The archetype, LJ-26, was demonstrated to recognize a clan-specific surface expressed in diverse mammalian, and also the Xenopus and chicken, immune systems. In flow-cytometric studies with LJ-26, we found that treatment of heterozygous T15i transgenic mice with a model B cell superantigen induced a clan III-restricted clonal deletion. These studies demonstrate the utility of a novel recombinant serologic reagent to study the composition of the B cell compartment and also the consequences of B cell superantigen exposure.

Amino Acid Sequence↗
PubMed2000

Neo-self antigens and the expansion of B-1 cells: lessons from atherosclerosis-prone mice.

The pathogenesis of atherosclerosis involves an inflammatory process that is modulated by the immune system, and within these complex responses we have discerned a possible role for an archetypic B-1 clone. We speculate that due to their immunogenicity and in vivo distribution the "neo"-self determinants created in oxidatively modified LDL are highly stimulatory for certain B-1 cell clones. These neo-self determinants, which can be created chemically, by somatic processes, may in fact represent the molecular analogues of somatic maturation, or even aging. These changes, including those on non-protein antigens induced by oxidative metabolism, amongst others, create neo-determinants against which the host no doubt can not develop rigorous B-cell tolerance. The onset of expression of these oxidative neo-determinants relatively late in development may well serve a useful function for the highly evolved mammalian immune system, as targeting by evolutionarily selected B-1 clones may facilitate the amplification of other useful antibody-mediated physiologic functions. As in the case of the T15 clone, these antibodies may aid in protection against common microbial pathogens. Hence we postulate that during the evolution of the adaptive immune system the neo-self antigenic milieu may have been exploited for the natural selection of primordial clonal specificities. The T15 B-1 clone may then illustrate a common paradigm in which there has been natural selection based on utility for the defense of the individual from environmental threats, as well as for possible "housekeeping" role(s) and the maintenance of cellular homeostasis.

Animals↗
PubMed2000

Natural antibodies with the T15 idiotype may act in atherosclerosis, apoptotic clearance, and protective immunity.

The immune response to oxidized LDL (OxLDL) may play an important role in atherogenesis. Working with apoE-deficient mice, we isolated a panel of OxLDL-specific B-cell lines that secrete IgM Abs that specifically bind to oxidized phospholipids such as 1-palmitoyl-2-(5-oxovaleroyl)-sn-glycero-3-phosphorylcholine (POVPC). These Abs block uptake of OxLDL by macrophages, recognize similar oxidation-specific epitopes on apoptotic cells, and are deposited in atherosclerotic lesions. The Abs were found to be structurally and functionally identical to classic "natural" T15 anti-PC Abs that are of B-1 cell origin and are reported to provide optimal protection from virulent pneumococcal infection. These findings suggest that there has been natural selection for B-1 cells secreting oxidation-specific/T15 antibodies, both for their role in natural immune defense and for housekeeping roles against oxidation-dependent neodeterminants in health and disease.

Amino Acid Sequence↗
PubMed2000

CD5 is A potential selecting ligand for B-cell surface immunoglobulin: a possible role in maintenance and selective expansion of normal and malignant B cells.

Although the function of CD5 on B cells is unknown, previous studies suggested that CD5 interaction with V(H) framework regions of surface immunoglobulins (Igs) may contribute to survival and expansion of B cells. Here we used B-chronic lymphocytic leukemia (B-CLL) cells and transformed B-cell lines from normal and B-CLL patients to study CD5-Ig interactions. Immobilized Ig binds and permits isolation of CD5 from lysates of CD5-expressing cell lines. Immunoglobulins or Fab fragments of different V(H) families varied in their effectiveness as inhibitors of anti-CD5 staining of CLL cells, appendix and tonsil tissue sections. Human Ig also binds to purified recombinant CD5. We show here for the first time that the unconventional Ig-CD5 interaction maps to the extracellular CD5-D2 domain whereas conventional epitopes recognized by anti-CD5 antibodies are localized in the D1 domain of CD5. We propose that interactions of VH framework regions with CD5 as a ligand may maintain, select or expand normal, autoimmune or transformed B cells and also contribute to skewing of the normal V(H) repertoire.

Antibodies, Monoclonal↗
PubMed1999

The murine clan V(H) III related 7183, J606 and S107 and DNA4 families commonly encode for binding to a bacterial B cell superantigen.

Superantigens, by virtue of their unconventional binding interactions with Ag receptors, can simulate a large subset of mature lymphocytes in the repertoire. Recent studies have documented that in vivo exposure to the model bacterial B cell superantigen, Staphylococcal protein A (SpA), induces large scale effects on murine B-cell clonal selection by mechanism(s) that include deletion of supra-clonal sets. While the structural bases for the immunomodulatory properties of several T-cell superantigens have been well characterized, the requirements for murine Fab-binding of SpA remain incompletely defined. To investigate these structural requirements, a series of direct binding and inhibition studies were performed with a large panel of Moabs of diverse variable region gene usage. These studies confirm previous reports that superantigen binding is completely restricted to the products of clan V(H) III-related families, that include the small S107 and J606 families, and we also demonstrated that usage of the related small DNA4 family commonly correlates with weaker binding activity. Furthermore, our results document that genes from the largest clan V(H) III family, 7183, commonly encode for Fab-mediated binding of SpA, while antibodies from five other VH families, J558, Q52, Sm7, VH11 and VH12, did not display Fab-mediated SpA binding activity. By contributing to the essential foundation for understanding of the structural basis for binding interactions, these findings will aid interpretation of evolving observations regarding the clonal fates induced by in vivo B-cell superantigen exposure.

Amino Acid Sequence↗
PubMed1999

NSAIDs and the gastrointestinal tract: an update on recent progress.

This article outlines the mechanisms involved in specific cyclooxygenase-1 (COX-1) and cyclooxygenase-2 (COX-2) inhibition as they relate to the safety of nonsteroidal anti-inflammatory drug (NSAID) use. New advancements in COX-2 technology appear to improve the safety profile of NSAID therapy. Gastroenterologic issues such as ulcer disease and liver disease as related to these novel new medications are reviewed.

Anti-Inflammatory Agents, Non-Steroidal↗
PubMed1998

Structural basis of the gp120 superantigen-binding site on human immunoglobulins.

B cell superantigens (SAg) interact with normal human nonimmune Igs (Igs), independently of the light chain isotype, and activate a large proportion of the B cell repertoire. Recently, the major envelope protein of HIV-1, gp120, was found to exhibit SAg-like properties for B cells with potential pathologic consequences for the infected host. This unconventional mode of interaction contrasts with its binding to immunization-induced Abs, which requires the tertiary structure of the heavy and light chain variable regions. In this report, we have examined the structural basis of the interaction between human Igs and gp120. We found that gp120 binding is restricted to Igs from the V(H)3 gene family and that the two V(H) genes 3-23 and 3-30, known to be overutilized during all stages of B cell development, frequently impart gp120 binding. We also provide evidence that the viral gp120 SAg can interact with only a subset of the human V(H)3+ Igs that can convey binding to the prototypic bacterial B cell SAg protein A from Staphylococcus aureus. Finally, we have identified amino acid positions present primarily in the first and third framework regions of the Ig heavy chain variable region, outside the conventional hypervariable loops, which correlate with gp120 binding. In a three-dimensional sequence-homology model, these residues partially overlap with the predicted SAg protein A binding site for V(H)3+ Igs.

Amino Acid Sequence↗
PubMed1998

The dual phases of the response to neonatal exposure to a VH family-restricted staphylococcal B cell superantigen.

In vitro studies of several naturally occurring proteins have characterized VH family-specific B lymphocyte binding and stimulatory properties that appear analogous to those of T cell superantigens. To examine the in vivo consequences of exposure to a putative B cell superantigen, we treated neonatal BALB/c mice with a form of staphylococcal protein A (MS) devoid of Fcgamma binding activity, which retains the clan VHIII Fab binding specificity. In naive adults, about 5% of peripheral B cells and >13% of splenic IgM-secreting cells display MS binding activity, in association with high IgM and low IgG circulating anti-MS Ab titers. Neonatal exposure to MS elicited two distinct temporal phases of immune responsiveness. The early phase, representing the first approximately 5 wk of life, was associated with MS-specific B cell and T cell tolerance. Microfluorometric assays revealed that exposure caused a dramatic MS-specific B cell clonal loss in bone marrow and spleen, but levels normalized by about 3 wk of life. The late phase (>6 wk of age) was associated with spontaneous priming for MS-specific T cell responses and production of MS-specific IgG1 Abs despite long term persistently depressed in vivo and in vitro MS-specific IgM responses. In vivo challenge during the late phase induced high frequencies of MS-specific IgG-secreting cells, indicating recruitment of highly focused Ab responses that were predominantly encoded by rearrangements of the S107 family, a member of the VHIII clan. These studies document the immunodominance of the VH-restricted Fab binding site on staphylococcal protein A and demonstrate the diverse effects of a B cell superantigen on the emerging peripheral B cell compartment.

Animals↗
PubMed1998

B cell superantigens: possible roles in immunodeficiency and autoimmunity.

Lymphocyte antigen receptors have evolved for the discrimination of self and non-self structures and consequently the unconventional binding activities of superantigens pose a special set of potential hazards and opportunities for the immune system. This review presents recent evidence that certain naturally occurring proteins have the properties of B cell superantigens by virtue of their unconventional variable-region mediated interactions with soluble and membrane-bound immunoglobulins. The implications for B lymphocyte activation and clonal selection are discussed and we speculate how superantigens may influence the development of lymphocyte repertoires and the immune responses associated with certain autoimmune and immunodeficiency diseases.

Animals↗