PubMed Health⌕ Search

Biomedical subjects

Andreas Radbruch

Publications and source records attributed to Andreas Radbruch.

At least 37 records · Page 2Linked to original sources
PubMed2005

Long-lived plasma cells and their contribution to autoimmunity.

The current view holds that chronic autoimmune diseases are driven by the continuous activation of autoreactive B and T lymphocytes. However, despite the use of potent immunosuppressants, the production of autoantibodies may persist and contribute to the autoimmune pathology. We recently demonstrated in autoimmune mice that both short-lived plasmablasts and long-lived plasma cells are involved in autoantibody production. While anti-proliferative immunosuppressive therapy and monoclonal anti-CD20 antibody deplete short-lived plasmablasts, long-lived plasma cells survive and continue to produce (auto)antibodies. Thus, strategies for targeting long-lived plasma cells may provide potent new treatment modalities.

Animals↗
PubMed2004

Intravenous injection of a D1 protein of the Smith proteins postpones murine lupus and induces type 1 regulatory T cells.

T cells that recognize nucleoproteins are required for the production of anti-dsDNA Abs involved in lupus development. SmD1 83-119 (a D1 protein of the Smith (Sm) proteins, part of small nuclear ribonucleoprotein) was recently shown to provide T cell help to anti-dsDNA Abs in the NZB/NZW model of lupus. Using this model in the present study, we showed that high dose tolerance to SmD1 (600-1000 microg i.v. of SmD1(83-119) peptide/mo) delays the production of autoantibodies, postpones the onset of lupus nephritis as confirmed by histology, and prolongs survival. Tolerance to SmD1 83-119 was adoptively transferred by CD90+ T cells, which also reduce T cell help for autoreactive B cells in vitro. One week after SmD1 83-119 tolerance induction in prenephritic mice, we detected cytokine changes in cultures of CD90+ T and B220+ B cells with decreased IFN-gamma and IL-4 expression and an increase in TGFbeta. Increased frequencies of regulatory IFN-gamma+ and IL10+ CD4+ T cells were later detected. Such regulatory IL-10+/IFN-gamma+ type 1 regulatory T cells prevented autoantibody generation and anti-CD3-induced proliferation of naive T cells. In conclusion, these results indicate that SmD1 83-119 peptide may play a dominant role in the activation of helper and regulatory T cells that influence autoantibody generation and murine lupus.

Amino Acid Sequence↗
PubMed2004

Generation of migratory antigen-specific plasma blasts and mobilization of resident plasma cells in a secondary immune response.

Maintenance of protective humoral immunity depends on the generation and survival of antibody-secreting cells. The bone marrow provides niches for long-term survival of plasma cells generated in the course of systemic immune responses in secondary lymphoid organs. Here, we have analyzed migratory human plasma blasts and plasma cells after secondary vaccination with tetanus toxin. On days 6 and 7 after immunization, CD19(+)/CD27(high)/intracellular immunoglobulin G(high) (IgG(high))/HLA-DR(high)/CD38(high)/CD20(-)/CD95(+) tetanus toxin-specific antibody-secreting plasma blasts were released in large numbers from the secondary lymphoid organs into the blood. These cells show chemotactic responsiveness toward ligands for CXCR3 and CXCR4, probably guiding them to the bone marrow or inflamed tissue. At the same time, a population of CD19(+)/CD27(high)/intracellular IgG(high)/HLA-DR(low)/CD38(+)/CD20(-)/CD95(+) cells appeared in the blood in large numbers. These cells, with the phenotype of long-lived plasma cells, secreted antibodies of unknown specificity, not tetanus toxoid. The appearance of these plasma cells in the blood indicates successful competition for survival niches in the bone marrow between newly generated plasma blasts and resident plasma cells as a fundamental mechanism for the establishment of humoral memory and its plasticity.

Adult↗
PubMed2004

Differential regulation of P-selectin ligand expression in naive versus memory CD4+ T cells: evidence for epigenetic regulation of involved glycosyltransferase genes.

Lymphocytes are targeted to inflamed sites by specific "homing" and chemokine receptors. Most of them, including ligands for P- and E-selectin, are absent from naive CD4(+) T cells and become induced after activation and differentiation in effector/memory cells. Polarized effector cells are characterized by the rapid production of distinct cytokines upon restimulation. Their cytokine memory is in part controlled by epigenetic imprinting during differentiation. Here we ask whether a similar mechanism could regulate selectin ligand expression, mediating entry into inflamed sites, notably within the skin. We report that acquisition of selectin ligands by naive but not memory CD4(+) cells depends on progression through the G(1)/S phase of the cell cycle-a phase susceptible to modification of the chromatin structure. Cell-cycle arrest prevented transcriptional activation of glycosyltransferases involved in the generation of selectin ligands, suggesting that progression through the cell cycle is required to unlock their genes. Artificial DNA demethylation strongly increased the frequency of selectin ligand-expressing cells, suggesting that DNA methylation keeps transferase genes inaccessible in naive T cells. Due to these findings we propose that selectin-dependent inflammation-seeking properties are imprinted by epigenetic modifications upon T-cell differentiation into effector cells.

Animals↗
PubMed2004

Perspectives and limitations of gene expression profiling in rheumatology: new molecular strategies.

The deciphering of the sequence of the human genome has raised the expectation of unravelling the specific role of each gene in physiology and pathology. High-throughput technologies for gene expression profiling provide the first practical basis for applying this information. In rheumatology, with its many diseases of unknown pathogenesis and puzzling inflammatory aspects, these advances appear to promise a significant advance towards the identification of leading mechanisms of pathology. Expression patterns reflect the complexity of the molecular processes and are expected to provide the molecular basis for specific diagnosis, therapeutic stratification, long-term monitoring and prognostic evaluation. Identification of the molecular networks will help in the discovery of appropriate drug targets, and permit focusing on the most effective and least toxic compounds. Current limitations in screening technologies, experimental strategies and bioinformatic interpretation will shortly be overcome by the rapid development in this field. However, gene expression profiling, by its nature, will not provide biochemical information on functional activities of proteins and might only in part reflect underlying genetic dysfunction. Genomic and proteomic technologies will therefore be complementary in their scientific and clinical application.

Animals↗
PubMed2004

Short-lived plasmablasts and long-lived plasma cells contribute to chronic humoral autoimmunity in NZB/W mice.

The current view holds that chronic autoimmune diseases are driven by the continuous activation of autoreactive B and T lymphocytes. However, despite the use of potent immunosuppressive drugs designed to interfere with this activation the production of autoantibodies often persists and contributes to progression of the immunopathology. In the present study, we analyzed the life span of (auto)antibody-secreting cells in the spleens of NZB x NZW F1 (NZB/W) mice, a murine model of systemic lupus erythematosus. The number of splenic ASCs increased in mice aged 1-5 mo and became stable thereafter. Less than 60% of the splenic (auto)antibody-secreting cells were short-lived plasmablasts, whereas 40% were nondividing, long-lived plasma cells with a half-life of >6 mo. In NZB/W mice and D42 Ig heavy chain knock-in mice, a fraction of DNA-specific plasma cells were also long-lived. Although antiproliferative immunosuppressive therapy depleted short-lived plasmablasts, long-lived plasma cells survived and continued to produce (auto)antibodies. Thus, long-lived, autoreactive plasma cells are a relevant target for researchers aiming to develop curative therapies for autoimmune diseases.

Animals↗
PubMed2004

CD38 low IgG-secreting cells are precursors of various CD38 high-expressing plasma cell populations.

Despite the important role immunoglobulin G (IgG)-secreting plasma cells play in memory immune responses, the differentiation and homeostasis of these cells are not completely understood. Here, we studied the differentiation of human IgG-secreting cells ex vivo and in vitro, identifying these cells by the cellular affinity matrix technology. Several subpopulations of IgG-secreting cells were identified among the cells isolated from tonsils and bone marrow, particularly differing in the expression levels of CD9, CD19, and CD38. CD38 low IgG-secreting cells were present exclusively in the tonsils. A major fraction of these cells appeared to be early plasma cell precursors, as upon activation of B cells in vitro, IgG secretion preceded up-regulation of CD38, and on tonsillar sections, IgG-containing, CD38 low cells with a plasmacytoid phenotype were found in follicles, where plasma cell differentiation starts. A unitary phenotype of migratory peripheral blood IgG-secreting cells suggests that all bone marrow plasma cell populations share a common precursor cell. These data are compatible with a multistep model for plasma cell differentiation and imply that a common CD38 low IgG-secreting precursor gives rise to a diverse plasma cell compartment.

ADP-ribosyl Cyclase↗
PubMed2004

CD152 (CTLA-4) determines the unequal resistance of Th1 and Th2 cells against activation-induced cell death by a mechanism requiring PI3 kinase function.

Survival of antigen-experienced T cells is essential for the generation of adaptive immune responses. Here, we show that the genetic and antibody-mediated inactivation of CD152 (cytotoxic T lymphocyte antigen 4) in T helper (Th) effector cells reduced the frequency of nonapoptotic cells in a completely Fas/Fas ligand (FasL)-dependent manner. CD152 cross-linking together with stimulation of CD3 and CD28 on activated Th2 cells prevented activation-induced cell death (AICD) as a result of reduced Fas and FasL expression. Apoptosis protection conferred by CD152 correlated with the up-regulation of Bcl-2 and was mediated by phosphatidylinositol 3 kinase, which prevented FasL expression through the inhibitory phosphorylation of Forkhead transcription factor FKHRL1. We show that signals induced by CD152 act directly on activated T lymphocytes and, due to its differential surface expression on activated Th1 and Th2 cells, induce resistance to AICD mainly in Th2 cells.

Animals↗
PubMed2004

GATA-3 in human T cell helper type 2 development.

The delineation of the in vivo role of GATA-3 in human T cell differentiation is a critical step in the understanding of molecular mechanisms directing human immune responses. We examined T cell differentiation and T cell-mediated effector functions in individuals lacking one functional GATA-3 allele. CD4 T cells from GATA-3+/- individuals expressed significantly reduced levels of GATA-3, associated with markedly decreased T helper cell (Th)2 frequencies in vivo and in vitro. Moreover, Th2 cell-mediated effector functions, as assessed by serum levels of Th2-dependent immunoglobulins (Igs; IgG4, IgE), were dramatically decreased, whereas the Th1-dependent IgG1 was elevated compared with GATA-3+/+ controls. Concordant with these data, silencing of GATA-3 in GATA-3+/+ CD4 T cells with small interfering RNA significantly reduced Th2 cell differentiation. Moreover, GATA-3 mRNA levels increased under Th2-inducing conditions and decreased under Th1-inducing conditions. Taken together, the data strongly suggest that GATA-3 is an important transcription factor in regulating human Th2 cell differentiation in vivo.

Adolescent↗
PubMed2004

Antigen-specific cytometry--new tools arrived!

Until recently, immunofluorescence-based cytometry and cell sorting, which have now found their place in the repertoire of state-of-the-art technologies, have mostly served to identify and assess subsets of leukocytes and thereby to evaluate rather systemic changes of the immune system. A more detailed defined evaluation of immune responses was not possible for a long time. In particular, a focus of the cytometric analysis on those lymphocytes specifically recognizing a defined antigen was hampered due to technical limitations. Yet, traditional methods for the analysis of antigen-specific lymphocytes typically relied upon measurements of proliferation or cytokine expression in bulk cultures. In recent times, this hindrance has been overcome both for B and T lymphocytes. We review here the emerging field of antigen-specific cytometry and describe the most widely used state of the art and future technologies that offer exciting new options to analyze and isolate specifically those lymphocytes that are directly involved in the immune reaction to given antigens, options that have already spurred research, diagnosis, and therapy beyond scope.

B-Lymphocytes↗
PubMed2004

Transcriptional control networks of cell differentiation: insights from helper T lymphocytes.

Coordinated programs of gene expression during cell differentiation can be controlled by master transcription factors. The differentiation of helper T (Th) lymphocytes during the immune response has been shown to occur along alternative pathways designated as Th1 and Th2. Induction of the Th1 and Th2 pathways is associated with the conversely regulated expression of the master factors T-bet and GATA-3, respectively. Both autoactivation and inhibition of GATA-3 play a crucial role in this process. We develop mathematical models of the underlying regulatory networks to provide a framework for the analysis of experimental data. Modeling concepts for gene expression dynamics are introduced, and paradigms for the behavior of gene-regulatory networks are reviewed. A mechanistic model for the regulation of GATA-3 in Th cells is developed that accounts for autoactivation and regulation by external differentiation signals. This system works as a bistable switch that enables the triggering of a differentiation program by transient inductive signals. GATA-3 inhibitors (such as FOG-1 and ROG) modulate GATA-3 expression by yet unidentified mechanisms. Three potential modes of inhibition, sequestration by a binding protein, repression of basal transcription, and repression of autoactivation, are predicted to have distinct, and strongly concentration-dependent, regulatory effects on GATA-3 dynamics. Based on these results, we develop a model for the cross-regulation of the alternative Th1 and Th2 differentiation programs which are governed by the dynamics of T-bet and GATA-3, respectively. The steady states of this model correlate with naïve, Th1-polarized, and Th2-polarized phenotypes. Our analysis makes predictions on the stability of the Th1 and Th2 programs and raises questions on the relation between transcription factor regulation and epigenetic determination in cell differentiation.

Animals↗
PubMed2004

Plasma cell-like morphology of Th1-cytokine-producing cells associated with the loss of CD3 expression.

Here we clarified the morphology and phenotype of interleukin (IL)-17- and interferon (IFN)-gamma-producing cells in both in vitro and in vivo situations. Oligoclonal activation of normal peripheral blood mononuclear cells with the superantigen Staphylococcus aureus enterotoxin B and polyclonal activation with phorbol myristate acetate/phytohemagglutinin were used as in vitro models. This study was extended to various in vivo situations such as rheumatoid arthritis, dermatomyositis, and normal activated lymph nodes. The phenotype of IL-17- and IFN-gamma-producing cells was evaluated by immunohistochemistry using the CD3 and CD4 T-cell markers, the CD20, CD38, kappa and lambda light chain B-cell lineage markers. The expression of two chemokine receptors, CCR6 and CCR7, involved with their associated ligands CCL20 and CCL19/CCL21 in the migration of T lymphocytes, was evaluated in tissue sections. After both polyclonal and oligoclonal activation, IL-17+ and IFN-gamma+ cells acquired a plasma cell-like morphology associated with a high secretory activity, the reduced expression of CD3, and no change of CD4 expression. In rheumatoid arthritis, dermatomyositis, and activated lymph nodes, both IL-17- and IFN-gamma-producing cells had the same morphology. These Th1 cytokine-producing cells were CD4(+)-, CD3-, and B-cell lineage marker-negative. In both in vitro and in vivo situations, expression of CCR6 or CCR7 was not associated with a particular subset. In conclusion, activated T-helper CD4(+) T cells, by their release of cytokines, seem to have functional similarities with plasma cells secreting immunoglobulins.

Antigens, CD↗
PubMed2004

Membrane glucocorticoid receptors (mGCR) are expressed in normal human peripheral blood mononuclear cells and up-regulated after in vitro stimulation and in patients with rheumatoid arthritis.

Glucocorticoids mediate their therapeutic actions mostly by genomic effects via cytosolic receptors, but some effects are too rapid to be mediated by changes at the genomic level. The detailed mechanisms of these nongenomic actions are still unclear. Membrane-bound glucocorticoid receptors (mGCR) have been suggested to be involved, although their physiological existence in humans so far is hypothetical. For the first time we demonstrate the existence of mGCR on monocytes and B cells obtained from healthy blood donors using high-sensitivity immunofluorescent staining. Immunostimulation with lipopolysaccharide increases the percentage of mGCR-positive monocytes, which can be prevented by inhibiting the secretory pathway. Overexpression of the human glucocorticoid receptor alpha alone is not sufficient to enhance mGCR expression. These in vitro findings are consistent with our clinical observation that in patients with rheumatoid arthritis the frequency of mGCR positive monocytes is increased and positively correlated with disease activity. We conclude that mGCR are 1) indeed physiologically present in healthy blood donors, but remained unidentified by conventional techniques due to their small number per cell and 2) actively up-regulated and transported through the cell after immunostimulation. These receptors may reflect a feedback mechanism of the organism upon immunostimulation and/or play a role in pathogenesis.

Adolescent↗
PubMed2004

Immunoglobulin class switching: in vitro induction and analysis.

During an immune response, B lymphocytes can switch expression of immunoglobulin (Ig) class (isotype) from IgM to IgG, IgE, or IgA. This Ig class switch is based on a deoxyribonucleic acid (DNA) recombination event that results in an exchange of the gene segments coding for the constant region of the Ig heavy chain, although the Ig heavy chain variable region is retained. This process changes the effector functions of the corresponding antibody (Ab). Much of our current understanding of the molecular mechanisms of class switch recombination is based on the analysis of B cells induced to switch class of Ig in vitro. In vitro, murine and human naive B cells can be activated with bacterial lipopolysaccharides, anti-CD40 or CD40L, to undergo class switch recombination. Cytokine signals can direct class switch recombination to distinct classes; for example, interleukin-4 will target murine IgG1 and IgE, and human IgG4 and IgE. Here we describe the technologies for the isolation of B lymphocytes, their activation to class switching, and the analysis of Ig class switching.

Animals↗
PubMed2003

Substitution in position 3 of cyclosporin A abolishes the cyclophilin-mediated gain-of-function mechanism but not immunosuppression.

Binary complex formation between the immunosuppressive drug cyclosporin A (CsA) and cyclophilin 18 is the prerequisite for the ability of CsA to inhibit the protein phosphatase activity of calcineurin, a central mediator of antigen-receptor signaling. We show here that several CsA derivatives substituted in position 3 can inhibit calcineurin without prior formation of a complex with cyclophilin 18. [Methylsarcosine(3)]CsA was shown to inhibit calcineurin, either in its free form with an IC(50) value of 10 microm, or in its complex form with cyclophilin 18 with an IC(50) of 500 nm. [Dimethylaminoethylthiosarcosine(3)]CsA ([Dat-Sar(3)]CsA) was found to inhibit calcineurin on its own, with an IC(50) value of 1.0 microm, but was not able to inhibit calcineurin after forming the [Dat-Sar(3)]CsA-cyclophilin 18 binary complex. Despite their different inhibitory properties, both CsA and [Dat-Sar(3)]CsA suppressed T cell proliferation and cytokine production mainly through blocking NFAT activation and interleukin-2 gene expression. Furthermore, to demonstrate that [Dat-Sar(3)]CsA can inhibit calcineurin in a cyclophilin-independent manner in vivo, we tested its effect in a Saccharomyces cerevisiae strain (Delta12), in which all the 12 cyclophilins and FKBPs were deleted. [Dat-Sar(3)]CsA, but not CsA, bypassed the requirement for cellular cyclophilins and caused growth inhibition in the salt-stressed Delta12 strain.

Amino Acid Substitution↗
PubMed2003

Diversity of clonal T cell proliferation is mediated by differential expression of CD152 (CTLA-4) on the cell surface of activated individual T lymphocytes.

Inhibitory effects of CD152 (CTLA-4) engagement during T cell activation have been described. To date, such effects could only be correlated to CD152 expression at the population level because expression of CD152 on the cell surface is too low to be assessed by conventional immunofluorescence on the single cell level. In this study, we use magnetofluorescent liposomes for the immunofluorescent detection of surface CD152-expressing CD4(+) T cells and show that, despite the fact that nearly all cells express intracellular CD152, only a fraction of 12% of activated T cells expresses surface CD152 at any given time point. Surface CD152(+) T cells appear with similar kinetics after primary or secondary activation in vitro. However, the frequency of surface CD152(+) T cells 48 h postactivation is 2-fold higher during secondary activation. Surface expression of CD152 is independent of the proliferative history of an activated T cell. Instruction of T cells for surface expression of CD152 rather depends on the time elapsed since the onset of activation, with a maximum at 48 h, and requires less than 12 h of Ag exposure. CD152(-) T cells, when isolated by cell sorting and restimulated, continue to proliferate. CD152 blockade has no effect on their proliferation. Isolated surface CD152(+) T cells do not proliferate upon restimulation unless CD152 is blocked. CD152 thus acts directly and autonomously on individual activated and proliferating T lymphocytes. Due to its heterogeneous expression on the cell surface of activated Th cells, CD152 might diversify the T cell response.

Animals↗
PubMed2003

Establishment of memory for IL-10 expression in developing T helper 2 cells requires repetitive IL-4 costimulation and does not impair proliferation.

T helper (Th) lymphocytes can develop memory for the expression of particular cytokines, like IL-4 or IL-10, in that reexpression of those cytokines is independent of the original costimulatory signal IL-4 and depends only on T cell receptor stimulation. Here, we show that in the course of Th2 cell differentiation in vitro, IL-4 memory is established during primary activation of naïve Th cells, whereas the establishment of IL-10 memory requires repetitive stimulation of the Th cell with IL-4 and T cell receptor. Likewise, established IL-10 memory, maintained in the absence of further IL-4 signals, was observed in individual IL-10-producing cells generated from in vivo antigen-experienced CD62L(low) Th cells and isolated by using the newly developed cytometric cytokine secretion assay for IL-10. In naïve Th cells undergoing primary activation, the induction of both IL-4 and IL-10 memory requires DNA synthesis, but reexpression of the cytokine genes can occur throughout cell cycle. In in vitro polarized Th2 cell populations, Th cells with IL-4 or IL-10 memory do not differ in proliferative behavior. Populations of Th cells isolated from polarized Th2 cultures according to expression of IL-4 or IL-10 also do not differ in proliferative behavior. Their proliferation mainly depends on IL-2. Thus, effector memory Th lymphocytes with memory for IL-4 or IL-10 expression are not intrinsically impaired in their proliferative potential and can play an essential role in reactive immunological memory and its regulation.

Animals↗