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Biomedical subjects

David I Stott

Publications and source records attributed to David I Stott.

11 recordsLinked to original sources
PubMed2006

Identification of hepatitis A virus mimotopes by phage display, antigenicity and immunogenicity.

A phage-displayed peptide approach was used to identify ligands mimicking antigenic determinants of hepatitis A virus (HAV) for the first time. Bacteriophages displaying HAV mimotopes were isolated from a phage-display peptide library by affinity selection on serum antibodies from hepatitis A patients. Selected phage-peptides were screened for reactivity with sera from HAV infected patients and healthy controls. Four cloned peptides with different sequences were identified as mimotopes of HAV; three of them showed similarity in their amino acid sequences with at least one of the VP3 and VP1 antigenic proteins of HAV. One clone was recognised by 92% of the positive sera. The phagotopes competed effectively with HAV for absorption of anti-HAV-specific antibodies in human sera, as determined by ELISA. The four phage clones induced neutralising anti-HAV antibodies in immunised mice. These results demonstrate the potential of this method to elucidate the disease related epitopes of HAV and to use these mimotopes in diagnostic applications or in the development of a mimotope-based hepatitis A vaccine without the necessity of manipulation of the virus.

Amino Acid Sequence↗
PubMed2006

Gene conversion in human rearranged immunoglobulin genes.

Over the past 20 years, many DNA sequences have been published suggesting that all or part of the V(H) segment of a rearranged immunoglobulin gene may be replaced in vivo. Two different mechanisms appear to be operating. One of these is very similar to primary V(D)J recombination, involving the RAG proteins acting upon recombination signal sequences, and this has recently been proven to occur. Other sequences, many of which show partial V(H) replacements with no addition of untemplated nucleotides at the V(H)-V(H) joint, have been proposed to occur by an unusual RAG-mediated recombination with the formation of hybrid (coding-to-signal) joints. These appear to occur in cells already undergoing somatic hypermutation in which, some authors are convinced, RAG genes are silenced. We recently proposed that the latter type of V(H) replacement might occur by homologous recombination initiated by the activity of AID (activation-induced cytidine deaminase), which is essential for somatic hypermutation and gene conversion. The latter has been observed in other species, but not in human Ig genes, so far. In this paper, we present a new analysis of sequences published as examples of the second type of rearrangement. This not only shows that AID recognition motifs occur in recombination regions but also that some sequences show replacement of central sections by a sequence from another gene, similar to gene conversion in the immunoglobulin genes of other species. These observations support the proposal that this type of rearrangement is likely to be AID-mediated rather than RAG-mediated and is consistent with gene conversion.

Base Sequence↗
PubMed2005

Immunoglobulin variable-region gene mutational lineage tree analysis: application to autoimmune diseases.

Lineage trees have frequently been drawn to illustrate diversification, via somatic hypermutation (SHM), of immunoglobulin variable-region (IGV) genes. In order to extract more information from IGV sequences, we developed a novel mathematical method for analyzing the graphical properties of IgV gene lineage trees, allowing quantification of the differences between the dynamics of SHM and antigen-driven selection in different lymphoid tissues, species, and disease situations. Here, we investigated trees generated from published IGV sequence data from B cell clones participating in autoimmune responses in patients with Myasthenia Gravis (MG), Rheumatoid Arthritis (RA), and Sjögren's Syndrome (SS). At present, as no standards exist for cell sampling and sequence extraction methods, data obtained by different research groups from two studies of the same disease often vary considerably. Nevertheless, based on comparisons of data groups within individual studies, we show here that lineage trees from different individual patients are often similar and can be grouped together, as can trees from two different tissues in the same patient, and even from IgG- and IgA-expressing B cell clones. Additionally, lineage trees from most studies reflect the chronic character of autoimmune diseases.

Arthritis, Rheumatoid↗
PubMed2005

Tumor-infiltrating B cell immunoglobulin variable region gene usage in invasive ductal breast carcinoma.

A major focus of tumor immunology is to reveal the potential role and capacity of immunocompetent cells found in different solid tumor tissues. The most abundant infiltrating cells (TIL), the T lymphocytes have been investigated in details concerning T-cell receptor usage and specificity. However, B cells have hardly been investigated in this respect, although high cellular B-cell infiltration has been correlated with improved patients' survival in some breast carcinomas. This led to our objectives to study variable region gene usage of the tumor-infiltrating B cells in different breast carcinoma types. By defining the immunoglobulin repertoire of the tumor-infiltrating B lymphocytes in the most common invasive ductal carcinoma (IDC) of the breast we compared it to the rare medullary breast carcinoma (MBC). After phenotyping infiltrating ductal carcinomas, B cells were obtained from tumor tissue by microdissection technique. Numerous rearranged TIL-B immunoglobulin heavy chain V genes (VH) were amplified, cloned, sequenced, and comparatively analyzed. Some characteristics were found for both breast carcinoma types. The immunoglobulins produced by TIL-B in ductal carcinoma are highly matured and oligoclonal. We conclude that Ig variable region gene usage reveals similar and distinguishable characteristics of TIL-B immunoglobulin repertoires, which are representative of the nature of the immune responses in invasive ductal and medullary breast carcinomas.

B-Lymphocytes↗
PubMed2005

Systemic autoimmune disease induced by dendritic cells that have captured necrotic but not apoptotic cells in susceptible mouse strains.

Systemic lupus erythematosus (SLE) is an autoimmune disorder of a largely unknown etiology. Anti-double-stranded (ds) DNA antibodies are a classic hallmark of the disease, although the mechanism underlying their induction remains unclear. We demonstrate here that, in both lupus-prone and normal mouse strains, strong anti-dsDNA antibody responses can be induced by dendritic cells (DC) that have ingested syngeneic necrotic (DC/nec), but not apoptotic (DC/apo), cells. Clinical manifestations of lupus were evident, however, only in susceptible mouse strains, which correlate with the ability of DC/nec to release IFN-gamma and to induce the pathogenic IgG2a anti-dsDNA antibodies. Injection of DC/nec not only accelerated disease progression in the MRL/MpJ-lpr/lpr lupus-prone mice but also induced a lupus-like disease in the MRL/MpJ-+/+ wild-type control strain. Immune complex deposition was readily detectable in the kidneys, and the mice developed proteinuria. Strikingly, female MRL/MpJ-+/+ mice that had received DC/nec, but not DC/apo, developed a 'butterfly' facial lesion resembling a cardinal feature of human SLE. Our study therefore demonstrates that DC/nec inducing a Th1 type of responses, which are otherwise tightly regulated in a normal immune system, may play a pivotal role in SLE pathogenesis.

Animals↗
PubMed2005

V(H) replacement in rearranged immunoglobulin genes.

Examples suggesting that all or part of the V(H) segment of a rearranged V(H)DJ(H) may be replaced by all or part of another V(H) have been appearing since the 1980s. Evidence has been presented of two rather different types of replacement. One of these has gained acceptance and has now been clearly demonstrated to occur. The other, proposed more recently, has not yet gained general acceptance because the same effect can be produced by polymerase chain reaction artefact. We review both types of replacement including a critical examination of evidence for the latter. The first type involves RAG proteins and recombination signal sequences (RSS) and occurs in immature B cells. The second was also thought to be brought about by RAG proteins and RSS. However, it has been reported in hypermutating cells which are not thought to express RAG proteins but in which activation-induced cytidine deaminase (AID) has recently been shown to initiate homologous recombination. Re-examination of the published sequences reveals AID target sites in V(H)-V(H) junction regions and examples that resemble gene conversion.

Gene Rearrangement, B-Lymphocyte, Heavy Chain↗
PubMed2004

Non-functional immunoglobulin G transcripts in a case of hyper-immunoglobulin M syndrome similar to type 4.

Summary 86% of immunoglobulin G (IgG) heavy-chain gene transcripts were found to be non-functional in the peripheral blood B cells of a patient initially diagnosed with common variable immunodeficiency, who later developed raised IgM, whereas no non-functionally rearranged transcripts were found in the cells of seven healthy control subjects. All the patient's IgM heavy-chain and kappa light-chain transcripts were functional, suggesting that either non-functional rearrangements were being selectively class-switched to IgG, or that receptor editing was rendering genes non-functional after class-switching. The functional gamma-chain sequences showed a normal rate of somatic hypermutation while non-functional sequences contained few somatic mutations, suggesting that most came from cells that had no functional gene and therefore were not receiving signals for hypermutation. However, apoptosis of peripheral blood lymphocytes was not impaired. No defects have been found in any of the genes currently known to be responsible for hyper-IgM syndrome but the phenotype fits best to type 4.

Adult↗
PubMed2003

Antigen-driven clonal proliferation, somatic hypermutation, and selection of B lymphocytes infiltrating human ductal breast carcinomas.

Infiltration of B lymphocytes into the tumor tissue of breast cancer patients is a common occurrence, but the role of these cells in the immune response to the tumor is unknown. Heavy B-cell infiltration in medullary breast carcinoma is well documented and associated with a more favorable prognosis, implying a positive role for the humoral immune response in elimination of tumor cells. Variable B-cell infiltration has also been detected in infiltrating ductal carcinomas of the breast, but little is known about the immunoglobulin gene repertoire of these tumor-infiltrating B lymphocytes and whether they are actively responding to a local stimulus or merely passive bystanders. We have therefore investigated the repertoire of B cells infiltrating four invasive ductal carcinomas. A group of 233 rearranged Ig V(H) genes was amplified, cloned, and sequenced from microdissected foci of infiltrating B cells. B cells within individual foci were polyclonal, and most were highly mutated. Several foci expressed dominant sets of V genes derived from B-cell clones. Some of these were found in more than one lymphoid cluster, indicating that B cells had migrated into the surrounding tissue and seeded new clusters. Analysis of the pattern of mutations in clonally related sets of Ig V genes expressed by tumor-infiltrating B cells shows that these cells are undergoing antigen-driven proliferation, somatic hypermutation, and affinity maturation in situ.

Antibody Affinity↗
PubMed2003

The VH gene repertoire of splenic B cells and somatic hypermutation in systemic lupus erythematosus.

In systemic lupus erythematosus (SLE) it has been hypothesized that self-reactive B cells arise from virgin B cells that express low-affinity, nonpathogenic germline V genes that are cross-reactive for self and microbial antigens, which convert to high-affinity autoantibodies via somatic hypermutation. The aim of the present study was to determine whether the VH family repertoire and pattern of somatic hypermutation in germinal centre (GC) B cells deviates from normal in SLE. Rearranged immunoglobulin VH genes were cloned and sequenced from GCs of a SLE patient's spleen. From these data the GC V gene repertoire and the pattern of somatic mutation during the proliferation of B-cell clones were determined. The results highlighted a bias in VH5 gene family usage, previously unreported in SLE, and under-representation of the VH1 family, which is expressed in 20-30% of IgM+ B cells of healthy adults and confirmed a defect in negative selection. This is the first study of the splenic GC response in human SLE.

B-Lymphocytes↗
PubMed2003

Complete analysis of the B-cell response to a protein antigen, from in vivo germinal centre formation to 3-D modelling of affinity maturation.

Somatic hypermutation of immunoglobulin variable region genes occurs within germinal centres (GCs) and is the process responsible for affinity maturation of antibodies during an immune response. Previous studies have focused almost exclusively on the immune response to haptens, which may be unrepresentative of epitopes on protein antigens. In this study, we have exploited a model system that uses transgenic B and CD4+ T cells specific for hen egg lysozyme (HEL) and a chicken ovalbumin peptide, respectively, to investigate a tightly synchronized immune response to protein antigens of widely differing affinities, thus allowing us to track many facets of the development of an antibody response at the antigen-specific B cell level in an integrated system in vivo. Somatic hypermutation of immunoglobulin variable genes was analysed in clones of transgenic B cells proliferating in individual GCs in response to HEL or the cross-reactive low-affinity antigen, duck egg lysozyme (DEL). Molecular modelling of the antibody-antigen interface demonstrates that recurring mutations in the antigen-binding site, selected in GCs, enhance interactions of the antibody with DEL. The effects of these mutations on affinity maturation are demonstrated by a shift of transgenic serum antibodies towards higher affinity for DEL in DEL-cOVA immunized mice. The results show that B cells with high affinity antigen receptors can revise their specificity by somatic hypermutation and antigen selection in response to a low-affinity, cross-reactive antigen. These observations shed further light on the nature of the immune response to pathogens and autoimmunity and demonstrate the utility of this novel model for studies of the mechanisms of somatic hypermutation.

Animals↗