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Martin Weigert

Publications and source records attributed to Martin Weigert.

16 recordsLinked to original sources
PubMed2006

Light chain editing generates polyreactive antibodies in chronic graft-versus-host reaction.

The chronic graft-versus-host (cGvH) reaction is a model of induced lupus caused by alloreactive CD4(+) T cells from a Bm-12 mouse in a C57BL/6 recipient. We used this cGvH reaction in C57BL/6 anti-DNA H chain transgenic mice, 56R/B6, to understand the structure, specificity, and origin of the induced autoantibodies (auto-Abs). We found anti-DNA Abs that reacted to several different antigens, such as phosphatidylserine, myelin basic protein, thyroglobulin, histone, insulin, cytochrome C, and beta-galactosidase. This polyreactivity was found for Abs from B cells that expressed the 56R H chain transgene with "editor" L chains that did not completely veto autoreactivity. We suggest that such incomplete editing results in polyreactivity and that incompletely edited polyreactive B cells influence the subsequent expression of pathogenic auto-Abs in disease. We also found B cells that coexpress kappa and lambda L chain. These B cells contributed to the autoimmune response and are possibly in the marginal zone of the spleen.

Animals↗
PubMed2006

Selection of anti-double-stranded DNA B cells in autoimmune MRL-lpr/lpr mice.

Abs to DNA and nucleoproteins are expressed in systemic autoimmune diseases, whereas B cells producing such Abs are edited, deleted, or inactivated in healthy individuals. Why autoimmune individuals fail to regulate is not well understood. In this study, we investigate the sources of anti-dsDNA B cells in autoimmune transgenic MRL-lpr/lpr mice. These mice are particularly susceptible to lupus because they carry a site-directed transgene, H76R that codes for an anti-DNA H chain. Over 90% of the B cells are eliminated in the bone marrow of these mice, and the few surviving B cells are associated with one of two Vkappa editors, Vkappa38c and Vkappa21D. Thus, it appears that negative selection by deletion and editing are intact in MRL-lpr/lpr mice. However, a population of splenic B cells in the H76R MRL-lpr/lpr mice produces IgG anti-nuclear Abs, and these mice have severe autoimmune organ damage. These IgG Abs are not associated with editors but instead use a unique Vkappa gene, Vkappa23. The H76R/Vkappa23 combination has a relatively high affinity for dsDNA and an anti-nuclear Ab pattern characteristic of lupus. Therefore, this Vkappa gene may confer a selective advantage to anti-DNA Abs in diseased mice.

Amino Acid Sequence↗
PubMed2006

Objective quality evaluation of fluorescence images to optimize automatic image acquisition.

BACKGROUND: Because different spectral sensitivities of human eye and image sensor lead to different perception of fluorescence signals, data generation is an important step in image analysis, because following work steps depend on it. METHODS: We developed a method to determine image parameters allowing an objective appraisal of quality of image data as well as a separation of object and background. RESULTS: Calculated parameters can be used for an automated adjustment of camera parameters in image analysis systems. DISCUSSION: Our approach for objective adjusted data generation achieves an improvement of analysis quality.

Cell Line, Tumor↗
PubMed2005

Control of genotypic allelic inclusion through TCR surface expression.

To gain insight into the molecular causes and functional consequences of allelic inclusion of TCR alpha-chains, we develop a computational model for thymocyte selection in which the signal that determines cell fate depends on surface expression. Analysis of receptor pairs on selected dual TCR cells reveals that allelic inclusion permits both autoreactive TCR and receptors not in the single TCR cell repertoire to be selected. However, in comparison with earlier theoretical studies, relatively few dual TCR cells display receptors with high avidity for thymic ligands because their alpha-chains compete aggressively for the beta-chain, which hinders rescue from clonal deletion. This feature of the model makes clear that allelic inclusion does not in itself compromise central tolerance. A specific experiment based on modulation of TCR surface expression levels is proposed to test the model.

Alleles↗
PubMed2005

T-cell epitope repertoire as predicted from human and viral genomes.

During thymic education, strongly self-reactive T cells are selected against, while weakly self-reactive cells are positively selected. However, the probability of an antigen being self derived and the number of self-peptides have never been properly defined. We merge algorithms for: cleavage prediction, TAP binding probability estimates and MHC binding properties to estimate the number and distribution of all MHC binding peptides. We show that the number of self-peptides with a high affinity to a given human MHC-I molecule is between 200 and almost 200,000 and is much less than the estimated total number of peptide sequences. This result suggests that MHC molecules are selected through evolution in order to reduce the number of self-peptides presented. The number of viral peptides presented is also low and varies between zero and a few hundred per virus for a given HLA allele. These low numbers explain the need for multiple alleles within an individual. We show that six codominantly expressed MHC-I alleles are sufficient to present at least one or two peptides per virus for the vast majority of viruses. Viruses can escape detection either by using peptides that cannot be presented on MHC molecules or by using peptides whose presented segments overlap significantly with self. Most viral families (such as influenza, HIV, Hepatitis and HPV) present as many peptides as predicted from their genome length, and overlap minimally with the human self-peptide repertoire. However, a few latent viruses, such as herpes and adenovirus share considerable peptide sequence homology with their human hosts.

Antigens, Viral↗
PubMed2004

Editing anti-DNA B cells by Vlambdax.

Receptor editing is performed by replacement of Vkappa genes that contribute to autoreactivity. In addition, the Ckappa locus can be deleted by Vkappa rearrangement to intronic or 3' of Ckappa RS sequences (also referred to as kappa deletion elements). B cells that delete the Ckappa can then express lambda light chains. However, the lambda locus, either of man or mouse, does not allow V gene replacement. Nor does it appear to be deleted. Therefore, editing of autoreactive lambda B cells may require alternative pathways. We have found that in anti-DNA heavy chain transgenic mice (tgs) VH3H9/56R, B cells that express anti-DNA receptors comprised of lambda1 in association with an anti-DNA heavy chain often coexpress a kappa chain that prevents DNA binding. We speculate that such isotypically included cells may have low anti-DNA receptor densities, a feature that may lead to self-tolerance. Here we describe a mechanism of preventing DNA binding by expression of a rarely used member of the Vlambda family, Vlambdax. The lambdax B cells of the tgs also express CD25 and may represent B cells that have exhausted light chain editing possibilities.

Animals↗
PubMed2003

Secondary heavy chain rearrangement: a mechanism for generating anti-double-stranded DNA B cells.

The chronic graft-versus-host (cGVH) reaction results in a syndrome that closely resembles systemic lupus erythematosus (SLE). It is induced in nonautoimmune mice by the transfer of alloreactive T cells. The availability of anti-DNA transgenes allows us to study the genetic origins of autoantibodies in this model. We induced cGVH in two anti-DNA H chain site-directed transgenic mouse strains. This resulted in clonal expansion and selection of specific mutations in the anti-double-stranded (ds) DNA B cell population. These data, together with a high frequency of anti-dsDNA B cell clones recovered as hybridomas, suggested that anti-dsDNAs are the product of an antigen-driven immune response. Genetic analysis associated this response with the generation of anti-dsDNA B cells through secondary rearrangements that replaced the site-directed transgene (sd-tg) with endogenous VH genes.

Amino Acid Sequence↗
PubMed2003

Dynamical analysis of a degenerate primary and secondary humoral immune response.

Lymphocyte receptor response to antigen is degenerate. Each receptor can have a high affinity to more than one antigen. The optimal level of degeneracy was previously modeled using different methods; all showing that the degeneracy level should be inversely proportional to the probability that an antigen belongs to the self repertoire. Here we develop a new formalism, reproducing the results of previous models, which enables us to study the relation between receptor degeneracy and the pathogen-immune cell interaction dynamics, in primary and secondary response. We begin by developing a general formalism and reproducing the results obtained by Nemazee: (1) that an optimal immune system will have a capacity which is inversely proportional to the fraction of self-antigens and (2) that the number of self-reactive cells that the body destroys is tuned by this capacity optimization to be 63%. We then use our extended framework to relate the minimal number of B cell precursor required to mount an immune response to the naive B cell production rate. Finally, we analyze the dynamics of the interaction between the immune system and a pathogen and show that memory cells may be used as the first line of defense, while newly created cells are used later to refine the immune response.

Animals↗
PubMed2003

Regulation of anti-phosphatidylserine antibodies.

The degree of heavy chain (H) editing, the types of Vkappa editors, and the pattern of Jkappa usage are correlated with a range of the affinity of anti-DNA. This range was determined by the number and location of arginine (R) residues in the VH. We, here, changed a key arginine residue in the VH of anti-DNA transgene to glycine, which sharply reduces the affinity for dsDNA. However, complete reversion of this anti-DNA to germline enhances the affinity for phosphatidylserine (PS). The B cells of this low-affinity anti-DNA and anti-PS transgenic mouse are tightly regulated by receptor editing. Thus, anti-PS B cells are another example of a constitutive self-antigen regulated in the bone marrow.

Animals↗
PubMed2002

Anti-DNA B cells in MRL/lpr mice show altered differentiation and editing pattern.

We have studied the regulation of anti-DNA B cells in transgenic mice with a heavy chain transgene (3H9H/56R). This transgene codes for a heavy chain that forms anti-double-stranded DNA (dsDNA) antibody when paired with most members of the endogenous Vkappa repertoire, but certain L chains, referred to as Vkappa editors, do not sustain dsDNA binding in combination with 3H9H/56R. In the nonautoimmune 3H9H/56R BALB/c, most B cells generated do not bind DNA because the transgene itself is edited or is associated with a Vkappa editor. A minor population of B cells (30%) bind dsDNA and express the lambda1 light chain (known to sustain 3H9H/56R DNA binding). These 3H9/56R/lambda1 B cells coexpress a kappa editor, and we propose that the down-regulation of the anti-DNA BCR caused by the dual L chain expression may prevent activation of this kappa/lambda population. These kappa/lambda B cells are sequestered in the marginal zone. Here, we studied the influence of autoimmunity on expression and regulation of 3H9H/56R. In 3H9H/56R MRL/lpr mice, the expression of anti-dsDNA is vastly accelerated. Anti-dsDNA B cells use noneditor kappas but, in addition, most anti-dsDNA B cells have edited the heavy chain transgene. lambda1 B cells (without the coexpression of a kappa editor) are found and the kappa/lambda1 MZ population is absent. Our results suggest that improper editing and failure to sequester autoreactive B cells may contribute to the breakdown of tolerance in MRL/lpr mice.

Amino Acid Sequence↗
PubMed2002

Chronic graft-versus-host in Ig knockin transgenic mice abrogates B cell tolerance in anti-double-stranded DNA B cells.

Anti-dsDNA Abs are specific diagnostic markers of systemic lupus erythematosus, and are also implicated in kidney pathology. Anti-dsDNA B cells have been shown to be tolerized in nonautoimmune mice. The immunodysregulation that causes these cells to break tolerance is presumably part of the fundamental defects in systemic lupus erythematosus. To explore these mechanisms, we used the chronic graft-versus-host model mediated by MHC class II differences. Induction of chronic graft-vs-host in anti-DNA H chain knockin (3H9.KI) transgenic mice on a nonautoimmune background resulted in specific activation of anti-dsDNA B cells, as evidenced by high titers of soluble Ab in sera and a high frequency (70%) of anti-dsDNA B cell clones recovered as hybridomas. In addition, the lambda(+)-anti-dsDNA B cells developed increased expression of cell surface activation markers, and concentrated in the T cell area of the follicle with an Ab-forming cell-compatible phenotype. Genetic analysis of the hybridoma clones showed strong evidence of secondary rearrangements of the L chain associated with anti-dsDNA reactivity. Thus, our study indicates that alloreactive T cell help can break tolerance in a complex manner, involving several events.

Animals↗
PubMed2002

Autoreactive B cells in the marginal zone that express dual receptors.

Allotype and isotype exclusion is a property of most lymphocytes. The reason for this property is not known but it guarantees a high concentration of a single receptor, and threshold numbers of receptors may be required for efficient positive and negative selection. Receptor editing compromises exclusion by sustaining recombination even after a functional receptor is formed. Consequently, B cells expressing multiple receptors arise. We have studied such B cells in which one of the two receptors is anti-self, and find that these partially autoreactive B cells accumulate in the marginal zone. The restriction of these cells in this location may help to prevent them from undergoing diversification and developing into fully autoreactive B cells.

Animals↗
PubMed2002

Analysis of B cell receptor production and rearrangement. Part I. Light chain rearrangement.

A probabilistic model of allelic exclusion fails to explain the status of receptor genes and the receptor phenotype of most B cells. A large proportion of B cells have incompletely rearranged H and/or L chain genes (e.g. kappa0/kappa+) and most B cells express only one receptor. These properties seem to require deterministic features of B cell development such as special mechanisms that stop rearrangement. However, receptor editing has revealed that rearrangement-stop is not stable and that multi-receptor lymphocytes make up a significant fraction of certain B and T cell populations. Consequently we have revived the purely probabilistic approach in a model that now includes receptor editing and allows for some multi-receptor B cells. We find that this model can explain the observed properties of B cells when the frequency of self-reactive B cells is high. Indeed, as we illustrate for anti-DNA, this is the case. Hence the probabilistic model has life and assiduous use of the model suggests unexpected but not unrealistic features of lymphocyte development.

Algorithms↗