| 1. |
- Greicius, Gediminas, et al.
(författare)
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Microvilli structures on B lymphocytes: inducible functional domains?
- 2004
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Ingår i: Int Immunol. - : Oxford University Press (OUP). - 0953-8178 .- 1460-2377. ; 16:2, s. 353-64
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Tidskriftsartikel (refereegranskat)abstract
- Interactive contact between B lymphocytes and T cells is necessary for their expansion during an immune response. It has been shown that B lymphocytes receive signals from T cells, such as IL-4 and cross-linking of CD40, which are crucial for their differentiation. We previously found that these factors induce formation of microvilli on B cells and that this was correlated with increased homotypic adhesion of B lymphocytes. In this study we have investigated if IL-4 induce segregation of proteins to microvilli and lipid rafts. Using immuno-electron microscopy we analyzed cell-surface distribution of molecules involved in B-T cell co-activation. Recruitment to detergent-resistant membrane fractions was analyzed using sucrose gradient centrifugation. We found that microvilli were enriched in ICAM-1 and MHC class II molecules. In contrast, LFA-1 and CD40 were more abundant on the smooth cell surfaces, while B7-2 (CD86) was randomly distributed. We also discovered that depletion of cholesterol, using beta-methyl-cyclodextrin, lowered the number of microvilli, indicating that intact lipid rafts are required for their expression. Moreover, activation of B lymphocytes by lipopolysaccharide (LPS) induced increased expression of GM(1), a marker for lipid rafts. However, although both surface and total levels of GM(1) were similar in B lymphocytes stimulated with either LPS or LPS plus IL-4, GM(1) was mainly expressed on microvilli in LPS plus IL-4-stimulated cells. Taken together, our results indicate that microvilli represent distinct inducible membrane domains that can regulate direct cell-cell interactions via grouping and three-dimensional presentation of cell-surface receptors.
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| 2. |
- Kis, Loránd L., et al.
(författare)
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The STAT6 signaling pathway activated by the cytokines IL-4 and IL-13 induces expression of the Epstein-Barr virus-encoded protein LMP-1 in absence of EBNA-2 : implications for the type II EBV latent gene expression in Hodgkin lymphoma
- 2011
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Ingår i: Blood. - : American Society of Hematology. - 0006-4971 .- 1528-0020. ; 117:1, s. 165-174
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Tidskriftsartikel (refereegranskat)abstract
- In line with the B-lymphotropic nature of EBV, the virus is present in several types of B cell lymphomas. EBV expresses a different set of latent genes in the associated tumors, such as EBNA-1 and LMPs (type II latency) in the classical Hodgkin lymphomas (cHL). We have previously reported that exposure of the in vitro EBV-converted, HL-derived cell line KMH2-EBV to CD40-ligand and IL-4 induced the expression of LMP-1. Here we show that exposure to IL-4 or IL-13 alone induced LMP-1 in the absence of EBNA-2. The induction of LMP-1 by IL-4 and IL-13 was mediated by the signal transducer STAT6 and a newly defined high-affinity STAT6-binding site in the LMP-1 promoter. IL-4 induced LMP-1 also in Burkitt lymphoma-derived lines and in tonsillar B cells infected with the EBNA-2-deficient EBV strain P3HR-1. Furthermore, co-culture of EBV-carrying BL cells with activated CD4(+) T cells resulted in the induction of LMP-1 in the absence of EBNA-2. As the Hodgkin/Reed-Sternberg are known to secrete IL-13, to have constitutively activated STAT6, and to be closely surrounded by CD4+ T cells, these mechanisms may be involved in the expression of LMP-1 in the EBV-positive cHLs.
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| 3. |
- Salmon, Daniel, et al.
(författare)
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Type I interferons directly down-regulate BCL-6 in primary and transformed germinal center B cells : Differential regulation in B cell lines derived from endemic or sporadic Burkitt's lymphoma
- 2012
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Ingår i: Cytokine. - : Elsevier BV. - 1043-4666 .- 1096-0023. ; 57:3, s. 360-371
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Tidskriftsartikel (refereegranskat)abstract
- Type I interferons (IFN) exert multiple effects on both the innate and adaptive immune system in addition to their antiviral and antiproliferative activities. Little is known, however about the direct effects of type IFNs on germinal center (GC) B cells, the central components of adaptive B cell responses. We used Burkitt's lymphoma (BL) lines, as a model system of normal human GC B cells, to examine the effect of type I IFNs on the expression of BCL-6, the major regulator of the GC reaction. We show that type I IFNs, but not IFN gamma, IL-2 and TNF alpha rapidly down-regulate BCL-6 protein and mRNA expression, in cell lines derived from endemic, but not from sporadic BL. IFN alpha-induced down-regulation is specific for BCL-6, independent of Epstein-Barr virus and is not accompanied by IRF-4 up-regulation. IFN alpha-induced BCL-6 mRNA down-regulation does not require de novo protein synthesis and is specifically inhibited by piceatannol. The proteasome inhibitor mG132 non-specifically prevents, while inhibitors of alternate type I IFN signaling pathways do not inhibit IFNa-induced BCL-6 protein downregulation. We validate our results with showing that IFN alpha rapidly down-regulates BCL-6 mRNA in purified mouse normal GC B cells. Our results identify type I IFNs as the first group of cytokines that can down-regulate BCL-6 expression directly in GC B cells.
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| 4. |
- Dahlberg, Carin I. M., et al.
(författare)
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A Novel Mouse Model for the Hyper-IgM Syndrome : A Spontaneous Activation-Induced Cytidine Deaminase Mutation Leading to Complete Loss of Ig Class Switching and Reduced Somatic Hypermutation
- 2014
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Ingår i: Journal of Immunology. - : The American Association of Immunologists. - 0022-1767 .- 1550-6606. ; 193:9, s. 4732-4738
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Tidskriftsartikel (refereegranskat)abstract
- We describe a spontaneously derived mouse line that completely failed to induce Ig class switching in vitro and in vivo. The mice inherited abolished IgG serum titers in a recessive manner caused by a spontaneous G -> A transition mutation in codon 112 of the aicda gene, leading to an arginine to histidine replacement (AID(R112H)). Ig class switching was completely reconstituted by expressing wild-type AID. Mice homozygous for AID(R112H) had peripheral B cell hyperplasia and large germinal centers in the absence of Ag challenge. Immunization with SRBCs elicited an Ag-specific IgG1 response in wild-type mice, whereas AID(R112H) mice failed to produce IgG1 and had reduced somatic hypermutation. The phenotype recapitulates the human hyper-IgM (HIGM) syndrome that is caused by point mutations in the orthologous gene in humans, and the AID(R112H) mutation is frequently found in HIGM patients. The AID(R112H) mouse model for HIGM provides a powerful and more precise tool than conventional knockout strategies.
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| 5. |
- Ding, Zhoujie, 1987-
(författare)
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Feedback Enhancement of Immune Responses by IgE, IgM, and IgG3 Antibodies
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Antibodies can enhance or suppress the immune responses against their specific antigens. This phenomenon is known as antibody-mediated feedback regulation. We have studied the mechanisms underlying IgE-, IgM-, and IgG3-mediated enhancement of immune responses in mouse models using intravenous immunization. We attempted to answer the following questions: 1) Which cell type presents IgE-complexed antigens to CD4+ T cells? 2) Is complement activation required for specific IgM to enhance antibody responses? 3) Does IgM enhance CD4+ T-cell responses? 4) How are IgG3-antigen complexes transported into B-cell follicles?We found that CD23+ B cells transporting IgE-antigen complexes into B-cell follicles were not required to prime the antigen-specific CD4+ T cells in vivo, whereas CD11c+ cells were indispensable. After examining the three most common subpopulations of CD11c+ cells in the spleen, we determined that it was CD8α- conventional dendritic cells migrating into the T-cell zone following immunization that presented IgE-complexed antigens to CD4+ T cells.Next, we showed that specific IgM from Cµ13 mice, which is unable to activate complement, failed to enhance either antibody or germinal center responses whereas wild-type IgM enhanced both responses. Therefore, specific IgM must activate complement to enhance humoral responses. In addition, wild-type IgM did not up-regulate CD4+ T-cell responses.Finally, we showed that IgG3-antigen complexes were transported by marginal zone B cells into B-cell follicles via binding to complement receptors 1 and 2 (CR1/2) on those cells. The immune complexes were captured by follicular dendritic cells as early as 2 h after immunization. Germinal center responses were also enhanced by IgG3. Using bone marrow chimeric mice, we found that CR1/2 expression was required on both marginal zone B cells and follicular dendritic cells to provide an optimal enhancement of antibody responses.
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| 6. |
- Gerasimcik, Natalija, 1980-
(författare)
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Activation, adhesion and motility of B lymphocytes in health and disease
- 2013
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- B cells can be activated by T cell-dependent stimuli, such as CD40 ligation and cytokines, which induce extensive proliferation, class switch recombination and somatic hypermutation.Epstein-Barr virus (EBV) can also induce B cell activation by mimicking T cell help through its main oncoprotein, latent membrane protein 1 (LMP-1). It is regulated by another EBV-encoded protein, EBV nuclear antigen 2 (EBNA-2), which is absent in Hodgkin and Burkitt lymphomas. We have studied LMP-1 induction by cytokines in vitro and shown that LMP-1 is induced through the transcription factor signal transducer and activator of transcription (STAT6) and a newly defined high-affinity STAT6-binding site.When IL-4 is added together with lipopolysaccharide (LPS) or α-CD40 to B cells, it induces homotypic round and tight aggregates in vitro, whereas LPS alone does not induce such morphological changes. I describe here attempts to identify the molecules that regulate these responses.I have shown that the Rho GTPase Cdc42 controls the spreading of B cells, whereas two other molecules in the same family, Rac1 and Rac2, control homotypic adhesion. Further, I have shown by conditional deletion of Cdc42 in B cells that it is important in the humoral immune response. Dock10 is a guanosine nucleotide exchange factor (GEF) for Cdc42. It is expressed through all differentiation stages of B cell development. However, targeted deletion of Dock10 in B cells does not result in an aberrant phenotype. Furthermore, by studying conditional knockout mice for Dock10, Cdc42, Rac1 and Rac2, I have elucidated the mechanism of cytoskeletal changes during B cell activation, leading to adhesion and motility.My results may lead to a better understanding of normal B cell activation and of EBV infection, which is associated with many human tumours and may help to understand cancer development and progression in B cells.
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| 7. |
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| 8. |
- Gerasimcik, Natalija, et al.
(författare)
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Deletion of Dock10 in B cells results in normal Development but a Mild Deficiency upon In Vivo and In Vitro stimulations
- 2017
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Ingår i: Frontiers in Immunology. - : Frontiers Media SA. - 1664-3224. ; 8
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Tidskriftsartikel (refereegranskat)abstract
- We sought to identify genes necessary to induce cytoskeletal change in B cells. Using gene expression microarray, we compared B cells stimulated with interleukin-4 (IL-4) and anti-CD40 antibodies that induce B cell spreading, cell motility, tight aggregates, and extensive microvilli with B cells stimulated with lipopolysaccharide that lack these cytoskeletal changes. We identified 84 genes with 10-fold or greater expression in anti-CD40 + IL-4 stimulated B cells, one of these encoded the guanine nucleotide exchange factor (GEF) dedicator of cytokinesis 10 (Dock10). IL-4 selectively induced Dock10 expression in B cells. Using lacZ expression to monitor Dock10 promoter activity, we found that Dock10 was expressed at all stages during B cell development. However, specific deletion of Dock10 in B cells was associated with a mild phenotype with normal B cell development and normal B cell spreading, polarization, motility, chemotaxis, aggregation, and Ig class switching. Dock10-deficient B cells showed lower proliferation in response to anti-CD40 and IL-4 stimulation. Moreover, the IgG response to soluble antigen in vivo was lower when Dock10 was specifically deleted in B cells. Together, we found that most B cell responses were intact in the absence of Dock10. However, specific deletion of Dock10 in B cells was associated with a mild reduction in B cell activation in vitro and in vivo.
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| 9. |
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| 10. |
- Gerasimcik, Natalija, et al.
(författare)
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The Rho GTPase Cdc42 Is Essential for the Activation and Function of Mature B Cells
- 2015
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Ingår i: Journal of Immunology. - : The American Association of Immunologists. - 0022-1767 .- 1550-6606. ; 194:10, s. 4750-4758
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Tidskriftsartikel (refereegranskat)abstract
- The Rho GTPase Cdc42 coordinates regulation of the actin and the microtubule cytoskeleton by binding and activating the Wiskott-Aldrich syndrome protein. We sought to define the role of intrinsic expression of Cdc42 by mature B cells in their activation and function. Mice with inducible deletion of Cdc42 in mature B cells formed smaller germinal centers and had a reduced Ab response, mostly of low affinity to T cell-dependent Ag, compared with wild-type (WT) controls. Spreading formation of long protrusions that contain F-actin, microtubules, and Cdc42-interacting protein 4, and assumption of a dendritic cell morphology in response to anti-CD40 plus IL-4 were impaired in Cdc42-deficient B cells compared with WT B cells. Cdc42-deficient B cells had an intact migratory response to chemokine in vitro, but their homing to the B cell follicles in the spleen in vivo was significantly impaired. Cdc42-deficient B cells induced a skewed cytokine response in CD4(+) T cells, compared with WT B cells. Our results demonstrate a critical role for Cdc42 in the motility of mature B cells, their cognate interaction with T cells, and their differentiation into Ab-producing cells.
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