Absence of CD81 Paradoxically Results in a Hyper-IgM and IgG Response to T-Independent Antigens.

Blood ◽  
2006 ◽  
Vol 108 (11) ◽  
pp. 1719-1719
Author(s):  
Mrinmoy Sanyal ◽  
Tsipi Shoham ◽  
Rosemary Fernandez ◽  
Shoshana Levy
Keyword(s):  
B Cells ◽  
B Cell ◽  
Cell Activation ◽  
Cell Receptor ◽  
Cellular Interactions ◽  
B Cell Activation ◽  
Signaling Complex ◽  
Hyper Igm ◽  
Deficient Mice

Abstract The tetraspanin CD81 is required for numerous biological functions including fertilization, infection, cell migration and cellular interactions in the nervous and immune systems. In B cells CD81 is a component of the CD19/CD21 signaling complex. CD81 was shown to facilitate the redistribution of the B cell receptor (BCR) complex and CD21 into lipid rafts in response to co-engagement, and to modulate BCR signaling. In addition, CD81-deficient mice express low levels of cell surface CD19, thereby potentially altering signaling by the CD19/CD21 co-receptor complex. Interestingly, the onset of CD81 expression coincides with the onset of CD19 expression during B cell development. The foregoing observations suggest that CD81 might reduce the in vivo response of B cells to antigenic stimulation. To test this hypothesis we compared the response of CD81-deficient and wild type mice to T-independent (TNP-LPS) and T-dependent (TNP-KLH) antigens. Surprisingly, CD81-deficient mice mounted significantly higher IgM responses against both types of antigens. Moreover, the IgG response of CD81-deficient mice was stronger and persistent in response to T-independent antigen. We further found that CD81-deficient mice have an increase in bone marrow perisinusoidal B cells (IgM+IgD+). These cells are primarily responsible for mounting T-independent immune responses against blood-borne pathogens. In addition, CD81-deficient spleenic B cells have an intrinsic ability to produce higher amounts of IgM. These surprising results suggest that CD81 is involved in modulating B cell activation, particularly in response to infection.

Enhanced B Cell Activation in the Absence of CD81

Blood ◽  
2008 ◽  
Vol 112 (11) ◽  
pp. 2578-2578
Author(s):  
Mrinmoy Sanyal ◽  
Rosemary Fernandez ◽  
Shoshana Levy
Keyword(s):  
B Cells ◽  
B Cell ◽  
Cell Activation ◽  
Cell Receptor ◽  
Free Calcium ◽  
B Cell Activation ◽  
Membrane Reorganization ◽  
A Cell

Abstract CD81 is a component of the CD19/CD21 coreceptor complex in B cells. This tetraspanin molecule was previously shown to enable membrane reorganization in B cells responding to complement-bound antigens. Here we stimulated B cells via their B cell receptor (BCR) and demonstrate that Cd81−/− B cells fluxed higher intracellular free calcium ion along with increased phosphorylation of PLCγ2 and Syk. The stimulated Cd81−/− B cells also proliferated faster and secreted higher amounts of antibodies. Moreover, activation of the TLR4 pathway in Cd81−/− B cells induced increased proliferation and antibody secretion. Furthermore, Cd81−/− mice mounted a significantly higher immune response to T-cell independent antigens than their wildtype counterparts. Finally, analysis of Cd81−/− B cells that were generated by bone marrow transplantation into Rag1−/− mice confirmed a cell intrinsic hyperactive phenotype. Taken together, these results indicate that CD81 plays a negative role in B cell activation in vitro and in vivo.

The Voltage-Gated Proton Channel HVCN1 Co-Localizes with B Cell Receptor and Is Involved in Class Switch Recombination in Vivo

Blood ◽  
2008 ◽  
Vol 112 (11) ◽  
pp. 707-707 ◽  
Author(s):  
Melania Capasso ◽  
Mandeep K Bhamrah ◽  
Robert S Boyd ◽  
Kelvin Cain ◽  
Karen Pulford ◽  
...  
Keyword(s):  
B Cells ◽  
B Cell ◽  
Antigen Presentation ◽  
Cell Activation ◽  
Cell Clone ◽  
Cell Receptor ◽  
Proton Channel ◽  
B Cell Activation ◽  
Voltage Gated

Abstract HVCN1 is a highly-conserved voltage-gated proton channel. Voltage-gated proton currents have been recorded in lymphocytes but their functions in B cells remain unknown. We isolated HVCN1 in a proteomic survey of plasma membrane proteins in mantle cell lymphoma (MCL) in leukemic phase. In normal lymphocytes, HVCN1 expression was restricted to the B-cell lineage; HVCN1 was highly expressed in mantle zone cells but down-regulated in germinal center (GC) cells undergoing receptor affinity maturation and class-switch recombination (CSR). Highest level expression was also observed in Chronic Lymphocytic Leukemia (CLL) cells from the peripheral blood. In MCL tumors, HVCN1 was expressed in circulating cells but absent from involved lymph nodes, whereas in diffuse large B cell lymphoma (DLBCL), its expression correlated with cases with a low proliferation index. Thus, in both primary and neoplastic B cells, HVCN1 expression appears to be associated with a non-proliferative phenotype. In human primary resting B cells and B cell lines, HVCN1 directly interacted with the B cell receptor (BCR) complex, as shown by Igβ and HVCN1 reciprocal immunoprecipitation experiments. We also found by confocal microscopy and subcellular fractionation, that upon BCR engagement the channel was internalized with the antigen receptor and the two proteins co-migrated to the endo-lysosomal, MHC class II (MHC-II) containing compartments (MIICs). When overexpressed in a hen egg lysozyme (HEL)-specific B cell clone, LK35.2, HVCN1 showed a basal phosphorylation which increased with HEL stimulation. The increased phosphorylation corresponded to an increase in proton conductance, termed “enhanced gating mode” and it was PKC dependent. We then asked whether HVCN1 over-expression could influence MHC II antigen presentation and if the effect could be mediated by changes in MIICs pH. Indeed, presentation of HEL peptides to a T cell clone was impaired in LK35.2 and A20 D1.3 cells, where HVCN1 had been re-introduced; effect was stronger for plate-bound antigen than for soluble antigen. The reduced antigen presentation was accompanied by an increase in endo-lysosomal pH, from pH4.9 ± 0.2 to 6.3 ± 0.1 (which may reflect HVCN1 channel-mediated proton flux out of the organelles), as measured with an anti-IgM antibody conjugated to a pH sensitive dye in HVCN1 over-expressing cells. Evidently, the presence of HVCN1 leads to increased endo-lysosomal pH, consistent with H+ current from the lysosomal compartment into the cytosol. Hence, active antigen presenting cells, like GC cells, might down-regulate HVCN1 expression to maximize the effect of antigen presentation. In order to investigate the role of HVCN1 in vivo, we used a HVCN1-deficient mouse line generated by genetrap insertion. These mice showed no obvious changes in numbers or composition of B-cell subpopulations. Immunization of HVCN1-deficient mice with a T-dependent antigen resulted in a defect in CSR to all IgG subclasses, particularly marked for the IgG2b, whereas in contrast, no differences were observed in IgM secretion, suggesting a pivotal role for HVCN1 during antigen-driven B-cell activation and subsequent CSR. HVCN1 may influence B-cell activation through alteration of reactive oxygen species (ROS) as HVCN1-deficient B cells showed reduced ROS production following BCR activation, a sign of suboptimal NADPH oxidase activity. It has been postulated that proton channels are required to counterbalance the electrogenic activity of NADPH oxidase during ROS production. Our data suggest that this mechanism also occurs in vivo and shed new light on the role of ROS in B cell activation and downstream effects.

scholarly journals The B Cell Receptor Itself Can Activate Complement to Provide the Complement Receptor 1/2 Ligand Required to Enhance B Cell Immune Responses In Vivo

2003 ◽  
Vol 198 (4) ◽  
pp. 591-602 ◽  
Author(s):  
Joerg Rossbacher ◽  
Mark J. Shlomchik
Keyword(s):  
Immune Response ◽  
B Cells ◽  
Immune Responses ◽  
B Cell ◽  
Cell Activation ◽  
Cell Receptor ◽  
B Cell Receptor ◽  
Mutant Mice ◽  
B Cell Activation

B cells express complement receptors (CRs) that bind activated fragments of C3 and C4. Immunized CR knockout (KO) mice have lower antibody titers and smaller germinal centers (GCs), demonstrating the importance of CR signals for the humoral immune response. CR ligands were thought to be generated via complement fixation mediated by preexisting “natural” IgM or early Ab from inefficiently activated B cells. This concept was recently challenged by a transgenic (Tg) mouse model that lacks circulating antibody but still retains membrane IgM (mIgM) and mounts normal immune responses. To test whether CR ligands could be generated by the B cell receptor (BCR) itself, we generated similar mice carrying a mutated mIgM that was defective in C1q binding. We found that B cells from such mutant mice do not deposit C3 on B cells upon BCR ligation, in contrast to B cells from mIgM mice. This has implications for the immune response: the mutant mice have smaller GCs than mIgM mice, and they are particularly deficient in the maintenance of the GC response. These results demonstrate a new BCR-dependent pathway that is sufficient and perhaps necessary to provide a CR1/2 ligand that promotes efficient B cell activation.

Microsignalosomes: spatially resolved receptor signalling

2009 ◽  
Vol 37 (5) ◽  
pp. 1014-1018 ◽  
Author(s):  
Bebhinn Treanor ◽  
Naomi E. Harwood ◽  
Facundo D. Batista
Keyword(s):  
B Cells ◽  
B Cell ◽  
Cell Activation ◽  
Imaging Techniques ◽  
Adaptive Immune System ◽  
Cell Receptor ◽  
The Body ◽  
B Cell Activation ◽  
Molecular Events

B-cells are a critical component of the adaptive immune system. As such, B-cells survey the body and mount appropriate protective responses to pathogen-derived antigens, resulting in the production of specific antibodies and induction of immunological memory. Given the effectiveness of these responses in selectively eliminating pathogenic infections, it is clear that the processes underlying antigen-induced B-cell activation must be highly regulated. Somewhat surprisingly given the specialized function of these immune cells, the BCR (B-cell receptor) functions similarly to receptors of the tyrosine kinase family that are commonplace in biology, as BCR ligation with antigen leads to B-cell proliferation and differentiation. In the Lymphocyte Interaction Laboratory, we are particularly interested in characterizing the very early molecular events underlying B-cell activation using a combination of cutting-edge high-resolution and in vivo imaging techniques.

scholarly journals T Cell Accumulation in B Cell Follicles Is Regulated by Dendritic Cells and Is Independent of B Cell Activation

2003 ◽  
Vol 197 (2) ◽  
pp. 195-206 ◽  
Author(s):  
Simon Fillatreau ◽  
David Gray
Keyword(s):  
T Cells ◽  
Dendritic Cells ◽  
T Cell ◽  
B Cells ◽  
B Cell ◽  
Cell Activation ◽  
B Cell Activation ◽  
Cell Accumulation ◽  
Antigen Presenting ◽  
Deficient Mice

We investigated the mechanism of CD4 T cell accumulation in B cell follicles after immunization. Follicular T cell numbers were correlated with the number of B cells, indicating B cell control of the niche that T cells occupy. Despite this, we found no role for B cells in the follicular migration of T cells. Instead, T cells are induced to migrate into B cell follicles entirely as a result of interaction with dendritic cells (DCs). Migration relies on CD40-dependent maturation of DCs, as it did not occur in CD40-deficient mice but was reconstituted with CD40+ DCs. Restoration was not achieved by the activation of DCs with bacterial activators (e.g., lipopolysaccharide, CpG), but was by the injection of OX40L–huIgG1 fusion protein. Crucially, the up-regulation of OX40L (on antigen-presenting cells) and CXCR-5 (on T cells) are CD40-dependent events and we show that T cells do not migrate to follicles in immunized OX40-deficient mice.

scholarly journals PTIP chromatin regulator controls development and activation of B cell subsets to license humoral immunity in mice

2017 ◽  
Vol 114 (44) ◽  
pp. E9328-E9337 ◽  
Author(s):  
Dan Su ◽  
Stijn Vanhee ◽  
Rebeca Soria ◽  
Elin Jaensson Gyllenbäck ◽  
Linda M. Starnes ◽  
...  
Keyword(s):  
B Cells ◽  
B Cell ◽  
Humoral Immunity ◽  
Cell Activation ◽  
Cell Receptor ◽  
B Cell Receptor ◽  
Transactivation Domain ◽  
B Cell Activation ◽  
Chromatin Regulator ◽  
B Cell Subsets

B cell receptor signaling and downstream NF-κB activity are crucial for the maturation and functionality of all major B cell subsets, yet the molecular players in these signaling events are not fully understood. Here we use several genetically modified mouse models to demonstrate that expression of the multifunctional BRCT (BRCA1 C-terminal) domain-containing PTIP (Pax transactivation domain-interacting protein) chromatin regulator is controlled by B cell activation and potentiates steady-state and postimmune antibody production in vivo. By examining the effects of PTIP deficiency in mice at various ages during ontogeny, we demonstrate that PTIP promotes bone marrow B cell development as well as the neonatal establishment and subsequent long-term maintenance of self-reactive B-1 B cells. Furthermore, we find that PTIP is required for B cell receptor- and T:B interaction-induced proliferation, differentiation of follicular B cells during germinal center formation, and normal signaling through the classical NF-κB pathway. Together with the previously identified role for PTIP in promoting sterile transcription at the Igh locus, the present results establish PTIP as a licensing factor for humoral immunity that acts at several junctures of B lineage maturation and effector cell differentiation by controlling B cell activation.

scholarly journals Monovalent engagement of the BCR activates ovalbumin-specific transnuclear B cells

2014 ◽  
Vol 211 (2) ◽  
pp. 365-379 ◽  
Author(s):  
Ana M. Avalos ◽  
Angelina M. Bilate ◽  
Martin D. Witte ◽  
Albert K. Tai ◽  
Jiang He ◽  
...  
Keyword(s):  
B Cells ◽  
B Cell ◽  
Synthetic Peptides ◽  
Cell Activation ◽  
Cell Receptor ◽  
Fine Tuning ◽  
B Cell Activation ◽  
Cd40 Ligation ◽  
Peptide Antigen ◽  
Peptide Epitope

Valency requirements for B cell activation upon antigen encounter are poorly understood. OB1 transnuclear B cells express an IgG1 B cell receptor (BCR) specific for ovalbumin (OVA), the epitope of which can be mimicked using short synthetic peptides to allow antigen-specific engagement of the BCR. By altering length and valency of epitope-bearing synthetic peptides, we examined the properties of ligands required for optimal OB1 B cell activation. Monovalent engagement of the BCR with an epitope-bearing 17-mer synthetic peptide readily activated OB1 B cells. Dimers of the minimal peptide epitope oriented in an N to N configuration were more stimulatory than their C to C counterparts. Although shorter length correlated with less activation, a monomeric 8-mer peptide epitope behaved as a weak agonist that blocked responses to cell-bound peptide antigen, a blockade which could not be reversed by CD40 ligation. The 8-mer not only delivered a suboptimal signal, which blocked subsequent responses to OVA, anti-IgG, and anti-kappa, but also competed for binding with OVA. Our results show that fine-tuning of BCR-ligand recognition can lead to B cell nonresponsiveness, activation, or inhibition.

Critical Role for CD81 in B Cell Activation.

Blood ◽  
2007 ◽  
Vol 110 (11) ◽  
pp. 1342-1342
Author(s):  
Mrinmoy Sanyal ◽  
Rosemary Fernandez ◽  
Shoshana Levy
Keyword(s):  
B Cells ◽  
B Cell ◽  
Cell Activation ◽  
Cell Function ◽  
Calcium Influx ◽  
Critical Role ◽  
B Cell Lymphoma ◽  
Free Calcium ◽  
B Cell Activation ◽  
Deficient Mice

Abstract CD81 is a component of the CD19/CD21 signaling complex in B cells. CD81 was originally discovered as target of an anti-proliferative antibody in a human B cell lymphoma. However, the exact role of CD81 in B cell function is not known. Here we studied B cells from CD81 knockout mice. We demonstrate that upon BCR induction these B cells flux higher intracellular free calcium ion; increase the phosphorylation of BCR-related proximal and distal substrates and increase their proliferation. Similarly, polyclonal activation of CD81-deficient B cells with LPS induced increased proliferation and antibody secretion. Consistent with these intrinsic B cell capabilities, CD81-deficient mice mounted significantly higher immune response upon antigenic stimulation. In addition, bone marrow perisinusoidal B cells (IgM+IgD+) capable of mounting T-independent immune responses against blood-borne pathogens were over represented in CD81-deficient mice. These cells also displayed increased calcium influx kinetics as splenic B cells and produced higher amounts of antibody after polyclonal stimulation. Taken together, these results suggest that CD81 is involved in suppressing B cell activation.

scholarly journals Utilization of a photoactivatable antigen system to examine B-cell probing termination and the B-cell receptor sorting mechanisms during B-cell activation

2016 ◽  
Vol 113 (5) ◽  
pp. E558-E567 ◽  
Author(s):  
Jing Wang ◽  
Shan Tang ◽  
Zhengpeng Wan ◽  
Yiren Gao ◽  
Yiyun Cao ◽  
...  
Keyword(s):  
B Cells ◽  
B Cell ◽  
Single Molecule ◽  
Cell Activation ◽  
Cell Receptor ◽  
B Cell Receptor ◽  
Antigen Binding ◽  
B Cell Activation ◽  
Class I Mhc ◽  
Antigen System

Antigen binding to the B-cell receptor (BCR) induces several responses, resulting in B-cell activation, proliferation, and differentiation. However, it has been difficult to study these responses due to their dynamic, fast, and transient nature. Here, we attempted to solve this problem by developing a controllable trigger point for BCR and antigen recognition through the construction of a photoactivatable antigen, caged 4-hydroxy-3-nitrophenyl acetyl (caged-NP). This photoactivatable antigen system in combination with live cell and single molecule imaging techniques enabled us to illuminate the previously unidentified B-cell probing termination behaviors and the precise BCR sorting mechanisms during B-cell activation. B cells in contact with caged-NP exhibited probing behaviors as defined by the unceasing extension of membrane pseudopods in random directions. Further analyses showed that such probing behaviors are cell intrinsic with strict dependence on F-actin remodeling but not on tonic BCR signaling. B-cell probing behaviors were terminated within 4 s after photoactivation, suggesting that this response was sensitive and specific to BCR engagement. The termination of B-cell probing was concomitant with the accumulation response of the BCRs into the BCR microclusters. We also determined the Brownian diffusion coefficient of BCRs from the same B cells before and after BCR engagement. The analysis of temporally segregated single molecule images of both BCR and major histocompatibility complex class I (MHC-I) demonstrated that antigen binding induced trapping of BCRs into the BCR microclusters is a fundamental mechanism for B cells to acquire antigens.

scholarly journals Inhibition of the Jun N-Terminal Protein Kinase Pathway by SHIP-1, a Lipid Phosphatase That Interacts with the Adaptor Molecule Dok-3

2004 ◽  
Vol 24 (6) ◽  
pp. 2332-2343 ◽  
Author(s):  
Jeffrey D. Robson ◽  
Dominique Davidson ◽  
André Veillette
Keyword(s):  
B Cells ◽  
Protein Kinase ◽  
B Cell ◽  
Cell Activation ◽  
Cell Receptor ◽  
Negative Regulator ◽  
B Cell Activation ◽  
Terminal Protein ◽  
Lipid Phosphatase ◽  
Jnk Cascade

ABSTRACT Dok-3 is a Dok-related adaptor expressed in B cells and macrophages. Previously, we reported that Dok-3 is an inhibitor of B-cell activation in A20 B cells and that it associates with SHIP-1, a 5′ inositol-specific lipid phosphatase, as well as Csk, a negative regulator of Src kinases. Here, we demonstrate that Dok-3 suppresses B-cell activation by way of its interaction with SHIP-1, rather than Csk. Our biochemical analyses showed that the Dok-3-SHIP-1 complex acts by selectively inhibiting the B-cell receptor (BCR)-evoked activation of the Jun N-terminal protein kinase (JNK) cascade without affecting overall protein tyrosine phosphorylation or activation of previously described SHIP-1 targets like Btk and Akt/PKB. Studies of B cells derived from SHIP-1-deficient mice showed that BCR-triggered activation of JNK is enhanced in the absence of SHIP-1, implying that the Dok-3-SHIP-1 complex (or a related mechanism) is a physiological negative regulator of the JNK cascade in normal B cells. Together, these data elucidate the mechanism by which Dok-3 inhibits B-cell activation. Furthermore, they provide evidence that SHIP-1 can be a negative regulator of JNK signaling in B cells.

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