The Experts below are selected from a list of 1845 Experts worldwide ranked by ideXlab platform
Andrea Cerutti - One of the best experts on this subject based on the ideXlab platform.
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innate signals in mucosal Immunoglobulin Class Switching
The Journal of Allergy and Clinical Immunology, 2010Co-Authors: Irene Puga, Andrea Cerutti, Montserrat ColsAbstract:The intestinal mucosa contains large communities of commensal bacteria that process otherwise indigestible food components, synthesize essential vitamins, stimulate the maturation of the immune system, and form an ecologic niche that prevents the growth of pathogenic species. Conversely, the intestine provides the commensals with a stable habitat rich in energy derived from the ingested food. A delicate homeostatic balance maintains this mutualistic relationship without triggering a destructive inflammatory response. Commensals orchestrate intestinal homeostasis by entertaining an intimate dialogue with epithelial cells and immune cells lodged in the mucosa. Such a dialogue generates finely tuned signaling programs that ensure a state of hyporesponsiveness against noninvasive commensals and a state of active readiness against invasive pathogens. In this dialogue epithelial cells function as "interpreters" that continuously translate microbial messages to "instruct" immune cells as to the antigenic composition of the intestinal lumen. This education process initiates sophisticated defensive strategies that comprise massive production of IgA, a noninflammatory mucosal antibody Class that generates immunity while preserving homeostasis.
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epithelial cells trigger frontline Immunoglobulin Class Switching through a pathway regulated by the inhibitor slpi
Nature Immunology, 2007Co-Authors: April Chiu, Daniel M Knowles, Amy Chadburn, Meimei Shan, Malwina Buldys, Aihao Ding, Paul A Santini, Andrea CeruttiAbstract:Epithelial cells trigger frontline Immunoglobulin Class Switching through a pathway regulated by the inhibitor SLPI
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epithelial cells trigger frontline Immunoglobulin Class Switching through a pathway regulated by the inhibitor slpi
Nature Immunology, 2007Co-Authors: April Chiu, Daniel M Knowles, Amy Chadburn, Meimei Shan, Malwina Buldys, Aihao Ding, Paul A Santini, Andrea CeruttiAbstract:Epithelial cells (ECs) transport Class-switched Immunoglobulin G (IgG) and IgA antibodies across mucous membranes. Whether ECs initiate Class Switching remains unknown. Here we found that ECs lining tonsillar crypts formed pockets populated by B cells expressing activation-induced cytidine deaminase (AID), an enzyme associated with ongoing Class Switching. ECs released B cell-activating AID-inducing factors after sensing microbial products through Toll-like receptors. The resulting Class Switching was amplified by thymic stromal lymphopoietin, an epithelial interleukin 7-like cytokine that enhanced the B cell 'licensing' function of dendritic cells, and was restrained by secretory leukocyte protease inhibitor, an epithelial homeostatic protein that inhibited AID induction in B cells. Thus, ECs may function as mucosal 'guardians' orchestrating frontline IgG and IgA Class Switching through a Toll-like receptor-inducible signaling program regulated by secretory leukocyte protease inhibitor.NOTE: In the version of this article initially published online, the middle label above Figure 6c is incorrect. The correct label should be 'BAFF'. The error has been corrected for all versions of the article.
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mucosal epithelial cells initiate frontline Immunoglobulin Class Switching through an slpi regulated pathway
Blood, 2006Co-Authors: Andrea Cerutti, April Chiu, Amy Chadburn, Meimei Shan, Paul A Santini, Daniel M KnowlesAbstract:Introduction . Class Switching from IgM to IgG and IgA is central to immunity against microbes and usually occurs in draining lymph nodes and requires activation of B cells by CD4+ T cells expressing CD40 ligand. Growing evidence indicates that B cells can mount frontline IgG and IgA responses at mucosal sites of entry through an alternative CD40-independent pathway involving B cell-activating factor of the TNF family (BAFF, also known as BLyS) and a proliferation-inducing ligand (APRIL). These innate factors are usually produced by dendritic cells and stimulate B cells through at least three distinct receptors. Together with dendritic cells, epithelial cells have a key position at the host-environment interface. Therefore, we asked whether epithelial cells play a role in frontline antibody production. Methods . Tonsillar tissue sections from healthy donors were analyzed for expression of activation-induced cytidine deaminase (AID) by immunohistochemistry and in situ hybridization. A simplified in vitro model reproducing the geometry of mucosal surfaces was used to evaluate the role of epithelial cells in Class Switching. Briefly, primary epithelial cells and B cells were cultured in the upper and lower chambers, respectively, of a trans-well system. Monocyte-derived dendritic cells were positioned on a filter separating the two chambers. Various microbial product analogues were used to mimic infection. RNA interference was performed to knockdown BAFF in epithelial cells. AID expression, CSR, antibody production and signaling were evaluated in B cells as reported (Litinsky et al., Nat. Immunol.2002, 3:822–829; Qiao et al., Nat. Immunol.2006, 7:302–310). Results . We found that the upper respiratory mucosa of healthy subjects comprised intraepithelial pockets filled with B cells expressing AID, a DNA-editing enzyme associated with ongoing Class switch DNA recombination (CSR). Epithelial cells released innate Class switch-inducing factors, including BAFF, after sensing microbial products through TLRs, thereby inducing AID expression, CSR, and ultimately IgG and IgA production in neighboring B cells. Epithelial cell-induced antibodies comprised polyreactive IgG and IgA capable of recognizing multiple microbial determinants. Intraepithelial Class Switching was enhanced by thymic stromal lymphopoietin (TSLP), an epithelial IL-7-like cytokine that augments the innate B cell-licensing functions of dendritic cells, and restrained by secretory leukocyte protease inhibitor (SLPI), an epithelial alarm antiprotease that suppresses AID expression in activated B cells. Conclusions . The present findings indicate that epithelial cells function as non-immune sentinels capable to autonomously orchestrate compartmentalized IgG and IgA responses at the interface between host and environment. This implies that mucosal vaccines should activate both epithelial and immune cells to elicit optimal antibody production.
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Human immunodeficiency virus 1 Nef suppresses CD40-dependent Immunoglobulin Class Switching in bystander B cells
Nature Immunology, 2006Co-Authors: Xugang Qiao, Bing He, April Chiu, Daniel M Knowles, Amy Chadburn, Andrea CeruttiAbstract:Immunoglobulin Class Switching from Immunoglobulin M (IgM) to IgG and IgA is central to immunity against viruses and requires the activation of B cells by T cells via CD154 (CD40 ligand) and cytokines. These molecules limit their signaling activity in immune cells by turning on negative feedback proteins, including IκB and SOCS. We show here that negative factor (Nef) protein, an immunosuppressive human immunodeficiency virus 1 protein expressed and released by infected cells, penetrates B cells both in vivo and in vitro . Nef suppressed Immunoglobulin Class-switch DNA recombination by inducing IκBα and SOCS proteins, which blocked CD154 and cytokine signaling via NF-κB and STAT transcription factors. Thus, human immunodeficiency virus 1 may evade protective T cell–dependent IgG and IgA responses by 'hijacking' physiological feedback inhibitors in B cells via Nef.
April Chiu - One of the best experts on this subject based on the ideXlab platform.
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the transmembrane activator taci triggers Immunoglobulin Class Switching by activating b cells through the adaptor myd88
Nature Immunology, 2010Co-Authors: Raul Santamaria, April Chiu, Meimei Shan, Anne Puel, Montserrat Cols, Kang Chen, Irene Puga, Huabao Xiong, James B Bussel, Jeanine ReichenbachAbstract:BAFF and APRIL are innate immune mediators that trigger Immunoglobulin G (IgG) and IgA Class-switch recombination (CSR) in B cells by engaging the receptor TACI. The mechanism that underlies CSR signaling by TACI remains unknown. Here we found that the cytoplasmic domain of TACI encompasses a conserved motif that bound MyD88, an adaptor that activates transcription factor NF-kappaB signaling pathways via a Toll-interleukin 1 (IL-1) receptor (TIR) domain. TACI lacks a TIR domain, yet triggered CSR via the DNA-editing enzyme AID by activating NF-kappaB through a Toll-like receptor (TLR)-like MyD88-IRAK1-IRAK4-TRAF6-TAK1 pathway. TACI-induced CSR was impaired in mice and humans lacking MyD88 or the kinase IRAK4, which indicates that MyD88 controls a B cell-intrinsic, TIR-independent, TACI-dependent pathway for Immunoglobulin diversification.
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epithelial cells trigger frontline Immunoglobulin Class Switching through a pathway regulated by the inhibitor slpi
Nature Immunology, 2007Co-Authors: April Chiu, Daniel M Knowles, Amy Chadburn, Meimei Shan, Malwina Buldys, Aihao Ding, Paul A Santini, Andrea CeruttiAbstract:Epithelial cells trigger frontline Immunoglobulin Class Switching through a pathway regulated by the inhibitor SLPI
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epithelial cells trigger frontline Immunoglobulin Class Switching through a pathway regulated by the inhibitor slpi
Nature Immunology, 2007Co-Authors: April Chiu, Daniel M Knowles, Amy Chadburn, Meimei Shan, Malwina Buldys, Aihao Ding, Paul A Santini, Andrea CeruttiAbstract:Epithelial cells (ECs) transport Class-switched Immunoglobulin G (IgG) and IgA antibodies across mucous membranes. Whether ECs initiate Class Switching remains unknown. Here we found that ECs lining tonsillar crypts formed pockets populated by B cells expressing activation-induced cytidine deaminase (AID), an enzyme associated with ongoing Class Switching. ECs released B cell-activating AID-inducing factors after sensing microbial products through Toll-like receptors. The resulting Class Switching was amplified by thymic stromal lymphopoietin, an epithelial interleukin 7-like cytokine that enhanced the B cell 'licensing' function of dendritic cells, and was restrained by secretory leukocyte protease inhibitor, an epithelial homeostatic protein that inhibited AID induction in B cells. Thus, ECs may function as mucosal 'guardians' orchestrating frontline IgG and IgA Class Switching through a Toll-like receptor-inducible signaling program regulated by secretory leukocyte protease inhibitor.NOTE: In the version of this article initially published online, the middle label above Figure 6c is incorrect. The correct label should be 'BAFF'. The error has been corrected for all versions of the article.
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mucosal epithelial cells initiate frontline Immunoglobulin Class Switching through an slpi regulated pathway
Blood, 2006Co-Authors: Andrea Cerutti, April Chiu, Amy Chadburn, Meimei Shan, Paul A Santini, Daniel M KnowlesAbstract:Introduction . Class Switching from IgM to IgG and IgA is central to immunity against microbes and usually occurs in draining lymph nodes and requires activation of B cells by CD4+ T cells expressing CD40 ligand. Growing evidence indicates that B cells can mount frontline IgG and IgA responses at mucosal sites of entry through an alternative CD40-independent pathway involving B cell-activating factor of the TNF family (BAFF, also known as BLyS) and a proliferation-inducing ligand (APRIL). These innate factors are usually produced by dendritic cells and stimulate B cells through at least three distinct receptors. Together with dendritic cells, epithelial cells have a key position at the host-environment interface. Therefore, we asked whether epithelial cells play a role in frontline antibody production. Methods . Tonsillar tissue sections from healthy donors were analyzed for expression of activation-induced cytidine deaminase (AID) by immunohistochemistry and in situ hybridization. A simplified in vitro model reproducing the geometry of mucosal surfaces was used to evaluate the role of epithelial cells in Class Switching. Briefly, primary epithelial cells and B cells were cultured in the upper and lower chambers, respectively, of a trans-well system. Monocyte-derived dendritic cells were positioned on a filter separating the two chambers. Various microbial product analogues were used to mimic infection. RNA interference was performed to knockdown BAFF in epithelial cells. AID expression, CSR, antibody production and signaling were evaluated in B cells as reported (Litinsky et al., Nat. Immunol.2002, 3:822–829; Qiao et al., Nat. Immunol.2006, 7:302–310). Results . We found that the upper respiratory mucosa of healthy subjects comprised intraepithelial pockets filled with B cells expressing AID, a DNA-editing enzyme associated with ongoing Class switch DNA recombination (CSR). Epithelial cells released innate Class switch-inducing factors, including BAFF, after sensing microbial products through TLRs, thereby inducing AID expression, CSR, and ultimately IgG and IgA production in neighboring B cells. Epithelial cell-induced antibodies comprised polyreactive IgG and IgA capable of recognizing multiple microbial determinants. Intraepithelial Class Switching was enhanced by thymic stromal lymphopoietin (TSLP), an epithelial IL-7-like cytokine that augments the innate B cell-licensing functions of dendritic cells, and restrained by secretory leukocyte protease inhibitor (SLPI), an epithelial alarm antiprotease that suppresses AID expression in activated B cells. Conclusions . The present findings indicate that epithelial cells function as non-immune sentinels capable to autonomously orchestrate compartmentalized IgG and IgA responses at the interface between host and environment. This implies that mucosal vaccines should activate both epithelial and immune cells to elicit optimal antibody production.
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Human immunodeficiency virus 1 Nef suppresses CD40-dependent Immunoglobulin Class Switching in bystander B cells
Nature Immunology, 2006Co-Authors: Xugang Qiao, Bing He, April Chiu, Daniel M Knowles, Amy Chadburn, Andrea CeruttiAbstract:Immunoglobulin Class Switching from Immunoglobulin M (IgM) to IgG and IgA is central to immunity against viruses and requires the activation of B cells by T cells via CD154 (CD40 ligand) and cytokines. These molecules limit their signaling activity in immune cells by turning on negative feedback proteins, including IκB and SOCS. We show here that negative factor (Nef) protein, an immunosuppressive human immunodeficiency virus 1 protein expressed and released by infected cells, penetrates B cells both in vivo and in vitro . Nef suppressed Immunoglobulin Class-switch DNA recombination by inducing IκBα and SOCS proteins, which blocked CD154 and cytokine signaling via NF-κB and STAT transcription factors. Thus, human immunodeficiency virus 1 may evade protective T cell–dependent IgG and IgA responses by 'hijacking' physiological feedback inhibitors in B cells via Nef.
Amy Chadburn - One of the best experts on this subject based on the ideXlab platform.
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epithelial cells trigger frontline Immunoglobulin Class Switching through a pathway regulated by the inhibitor slpi
Nature Immunology, 2007Co-Authors: April Chiu, Daniel M Knowles, Amy Chadburn, Meimei Shan, Malwina Buldys, Aihao Ding, Paul A Santini, Andrea CeruttiAbstract:Epithelial cells trigger frontline Immunoglobulin Class Switching through a pathway regulated by the inhibitor SLPI
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epithelial cells trigger frontline Immunoglobulin Class Switching through a pathway regulated by the inhibitor slpi
Nature Immunology, 2007Co-Authors: April Chiu, Daniel M Knowles, Amy Chadburn, Meimei Shan, Malwina Buldys, Aihao Ding, Paul A Santini, Andrea CeruttiAbstract:Epithelial cells (ECs) transport Class-switched Immunoglobulin G (IgG) and IgA antibodies across mucous membranes. Whether ECs initiate Class Switching remains unknown. Here we found that ECs lining tonsillar crypts formed pockets populated by B cells expressing activation-induced cytidine deaminase (AID), an enzyme associated with ongoing Class Switching. ECs released B cell-activating AID-inducing factors after sensing microbial products through Toll-like receptors. The resulting Class Switching was amplified by thymic stromal lymphopoietin, an epithelial interleukin 7-like cytokine that enhanced the B cell 'licensing' function of dendritic cells, and was restrained by secretory leukocyte protease inhibitor, an epithelial homeostatic protein that inhibited AID induction in B cells. Thus, ECs may function as mucosal 'guardians' orchestrating frontline IgG and IgA Class Switching through a Toll-like receptor-inducible signaling program regulated by secretory leukocyte protease inhibitor.NOTE: In the version of this article initially published online, the middle label above Figure 6c is incorrect. The correct label should be 'BAFF'. The error has been corrected for all versions of the article.
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mucosal epithelial cells initiate frontline Immunoglobulin Class Switching through an slpi regulated pathway
Blood, 2006Co-Authors: Andrea Cerutti, April Chiu, Amy Chadburn, Meimei Shan, Paul A Santini, Daniel M KnowlesAbstract:Introduction . Class Switching from IgM to IgG and IgA is central to immunity against microbes and usually occurs in draining lymph nodes and requires activation of B cells by CD4+ T cells expressing CD40 ligand. Growing evidence indicates that B cells can mount frontline IgG and IgA responses at mucosal sites of entry through an alternative CD40-independent pathway involving B cell-activating factor of the TNF family (BAFF, also known as BLyS) and a proliferation-inducing ligand (APRIL). These innate factors are usually produced by dendritic cells and stimulate B cells through at least three distinct receptors. Together with dendritic cells, epithelial cells have a key position at the host-environment interface. Therefore, we asked whether epithelial cells play a role in frontline antibody production. Methods . Tonsillar tissue sections from healthy donors were analyzed for expression of activation-induced cytidine deaminase (AID) by immunohistochemistry and in situ hybridization. A simplified in vitro model reproducing the geometry of mucosal surfaces was used to evaluate the role of epithelial cells in Class Switching. Briefly, primary epithelial cells and B cells were cultured in the upper and lower chambers, respectively, of a trans-well system. Monocyte-derived dendritic cells were positioned on a filter separating the two chambers. Various microbial product analogues were used to mimic infection. RNA interference was performed to knockdown BAFF in epithelial cells. AID expression, CSR, antibody production and signaling were evaluated in B cells as reported (Litinsky et al., Nat. Immunol.2002, 3:822–829; Qiao et al., Nat. Immunol.2006, 7:302–310). Results . We found that the upper respiratory mucosa of healthy subjects comprised intraepithelial pockets filled with B cells expressing AID, a DNA-editing enzyme associated with ongoing Class switch DNA recombination (CSR). Epithelial cells released innate Class switch-inducing factors, including BAFF, after sensing microbial products through TLRs, thereby inducing AID expression, CSR, and ultimately IgG and IgA production in neighboring B cells. Epithelial cell-induced antibodies comprised polyreactive IgG and IgA capable of recognizing multiple microbial determinants. Intraepithelial Class Switching was enhanced by thymic stromal lymphopoietin (TSLP), an epithelial IL-7-like cytokine that augments the innate B cell-licensing functions of dendritic cells, and restrained by secretory leukocyte protease inhibitor (SLPI), an epithelial alarm antiprotease that suppresses AID expression in activated B cells. Conclusions . The present findings indicate that epithelial cells function as non-immune sentinels capable to autonomously orchestrate compartmentalized IgG and IgA responses at the interface between host and environment. This implies that mucosal vaccines should activate both epithelial and immune cells to elicit optimal antibody production.
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Human immunodeficiency virus 1 Nef suppresses CD40-dependent Immunoglobulin Class Switching in bystander B cells
Nature Immunology, 2006Co-Authors: Xugang Qiao, Bing He, April Chiu, Daniel M Knowles, Amy Chadburn, Andrea CeruttiAbstract:Immunoglobulin Class Switching from Immunoglobulin M (IgM) to IgG and IgA is central to immunity against viruses and requires the activation of B cells by T cells via CD154 (CD40 ligand) and cytokines. These molecules limit their signaling activity in immune cells by turning on negative feedback proteins, including IκB and SOCS. We show here that negative factor (Nef) protein, an immunosuppressive human immunodeficiency virus 1 protein expressed and released by infected cells, penetrates B cells both in vivo and in vitro . Nef suppressed Immunoglobulin Class-switch DNA recombination by inducing IκBα and SOCS proteins, which blocked CD154 and cytokine signaling via NF-κB and STAT transcription factors. Thus, human immunodeficiency virus 1 may evade protective T cell–dependent IgG and IgA responses by 'hijacking' physiological feedback inhibitors in B cells via Nef.
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hiv 1 nef suppresses t cell dependent Immunoglobulin Class Switching by inducing inhibitors of cd40 and il 4 receptor signaling in bystander b cells
Blood, 2005Co-Authors: Andrea Cerutti, Daniel M Knowles, April Chiu, Amy Chadburn, Xugang QiaoAbstract:Background. Class switch DNA recombination (CSR) from IgM to IgG and IgA is central to immunity against pathogens and requires the activation of B cells by CD4 + T cells through CD40 ligand (CD40L) and cytokines, including IL-4 and IL-10. Viruses evade protective IgG and IgA responses through a number of strategies, including production of soluble proteins that suppress T cell-dependent (TD) Class Switching in bystander B cells. HIV-1 is thought to impair antigen-specific IgG and IgA production by inducing progressive depletion of CD4 + T cells. Although important, this mechanism is not sufficient to explain the intrinsically poor response of B cells from viremic patients to CD4 + T cell help. This prompted us to explore the B cell-modulating activity of negative factor (Nef), an early HIV-1 protein implicated in immunosuppression. Nef is released in the extracellular environment by infected cells and might perturb the function of bystander B cells by targeting them through its N-terminal myristoylated domain. Methods. Tonsillar tissue sections from healthy donors and lymph nodal tissue sections from 10 HIV-1-infected patients were analyzed for IgD, p24, and Nef expression by immunohistochemistry. Nef expression was also analyzed in IgD + B cells purified from healthy donors and exposed to a recombinant myristoylated or non-myristoylated Nef protein. These IgD+ B cells as well as an IgD + B cell line expressing a wild-type Nef transgene or a mutant Nef transgene lacking the myristoylated domain were utilized in CSR assays after further exposure to CD40L, IL-4 and IL-10. CSR and signaling were studied as described 1 , 2 , 3 . Results. We found that HIV-1-infected lymphoid follicles express large amounts of Nef. This viral protein penetrates in bystander B cells both in vivo and in vitro and interferes with the initiation of CSR by CD40L and cytokines without down-regulating CD40 and cytokine receptor expression on B cells. Rather, Nef up-regulates inhibitor of NF-κ B (Iκ B) and suppressor of cytokine signaling (SOCS) proteins, including SOCS1 and SOCS3, in B cells. These powerful inhibitory proteins attenuate the transcriptional activation of germline Ig gene promoters by blocking CD40 and cytokine receptor signaling through NF-κ B and signal transducer and activator of transcription (STAT), respectively. In addition, Nef hampers the up-regulation of key components of the CSR machinery, such as activation-induced cytidine deaminase (AID), and blocks the induction of IgG, IgA and IgE secretion by CD40L and cytokines. Under similar conditions, Nef spares B cell survival, B cell proliferation as well as B cell signaling through mitogen-activated protein kinase p38 and B cell-specific activation protein (BSAP or Pax5). Conclusions. Our findings suggest that HIV-1 inhibits IgG and IgA production not only by impairing CD4 + T cells, but also by turning on powerful CSR inhibitory pathways in bystander B cells through Nef. We propose that Nef-blocking agents might improve protective antibody responses to pathogens and vaccines in HIV-1-infected patients.
Daniel M Knowles - One of the best experts on this subject based on the ideXlab platform.
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epithelial cells trigger frontline Immunoglobulin Class Switching through a pathway regulated by the inhibitor slpi
Nature Immunology, 2007Co-Authors: April Chiu, Daniel M Knowles, Amy Chadburn, Meimei Shan, Malwina Buldys, Aihao Ding, Paul A Santini, Andrea CeruttiAbstract:Epithelial cells trigger frontline Immunoglobulin Class Switching through a pathway regulated by the inhibitor SLPI
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epithelial cells trigger frontline Immunoglobulin Class Switching through a pathway regulated by the inhibitor slpi
Nature Immunology, 2007Co-Authors: April Chiu, Daniel M Knowles, Amy Chadburn, Meimei Shan, Malwina Buldys, Aihao Ding, Paul A Santini, Andrea CeruttiAbstract:Epithelial cells (ECs) transport Class-switched Immunoglobulin G (IgG) and IgA antibodies across mucous membranes. Whether ECs initiate Class Switching remains unknown. Here we found that ECs lining tonsillar crypts formed pockets populated by B cells expressing activation-induced cytidine deaminase (AID), an enzyme associated with ongoing Class Switching. ECs released B cell-activating AID-inducing factors after sensing microbial products through Toll-like receptors. The resulting Class Switching was amplified by thymic stromal lymphopoietin, an epithelial interleukin 7-like cytokine that enhanced the B cell 'licensing' function of dendritic cells, and was restrained by secretory leukocyte protease inhibitor, an epithelial homeostatic protein that inhibited AID induction in B cells. Thus, ECs may function as mucosal 'guardians' orchestrating frontline IgG and IgA Class Switching through a Toll-like receptor-inducible signaling program regulated by secretory leukocyte protease inhibitor.NOTE: In the version of this article initially published online, the middle label above Figure 6c is incorrect. The correct label should be 'BAFF'. The error has been corrected for all versions of the article.
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mucosal epithelial cells initiate frontline Immunoglobulin Class Switching through an slpi regulated pathway
Blood, 2006Co-Authors: Andrea Cerutti, April Chiu, Amy Chadburn, Meimei Shan, Paul A Santini, Daniel M KnowlesAbstract:Introduction . Class Switching from IgM to IgG and IgA is central to immunity against microbes and usually occurs in draining lymph nodes and requires activation of B cells by CD4+ T cells expressing CD40 ligand. Growing evidence indicates that B cells can mount frontline IgG and IgA responses at mucosal sites of entry through an alternative CD40-independent pathway involving B cell-activating factor of the TNF family (BAFF, also known as BLyS) and a proliferation-inducing ligand (APRIL). These innate factors are usually produced by dendritic cells and stimulate B cells through at least three distinct receptors. Together with dendritic cells, epithelial cells have a key position at the host-environment interface. Therefore, we asked whether epithelial cells play a role in frontline antibody production. Methods . Tonsillar tissue sections from healthy donors were analyzed for expression of activation-induced cytidine deaminase (AID) by immunohistochemistry and in situ hybridization. A simplified in vitro model reproducing the geometry of mucosal surfaces was used to evaluate the role of epithelial cells in Class Switching. Briefly, primary epithelial cells and B cells were cultured in the upper and lower chambers, respectively, of a trans-well system. Monocyte-derived dendritic cells were positioned on a filter separating the two chambers. Various microbial product analogues were used to mimic infection. RNA interference was performed to knockdown BAFF in epithelial cells. AID expression, CSR, antibody production and signaling were evaluated in B cells as reported (Litinsky et al., Nat. Immunol.2002, 3:822–829; Qiao et al., Nat. Immunol.2006, 7:302–310). Results . We found that the upper respiratory mucosa of healthy subjects comprised intraepithelial pockets filled with B cells expressing AID, a DNA-editing enzyme associated with ongoing Class switch DNA recombination (CSR). Epithelial cells released innate Class switch-inducing factors, including BAFF, after sensing microbial products through TLRs, thereby inducing AID expression, CSR, and ultimately IgG and IgA production in neighboring B cells. Epithelial cell-induced antibodies comprised polyreactive IgG and IgA capable of recognizing multiple microbial determinants. Intraepithelial Class Switching was enhanced by thymic stromal lymphopoietin (TSLP), an epithelial IL-7-like cytokine that augments the innate B cell-licensing functions of dendritic cells, and restrained by secretory leukocyte protease inhibitor (SLPI), an epithelial alarm antiprotease that suppresses AID expression in activated B cells. Conclusions . The present findings indicate that epithelial cells function as non-immune sentinels capable to autonomously orchestrate compartmentalized IgG and IgA responses at the interface between host and environment. This implies that mucosal vaccines should activate both epithelial and immune cells to elicit optimal antibody production.
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Human immunodeficiency virus 1 Nef suppresses CD40-dependent Immunoglobulin Class Switching in bystander B cells
Nature Immunology, 2006Co-Authors: Xugang Qiao, Bing He, April Chiu, Daniel M Knowles, Amy Chadburn, Andrea CeruttiAbstract:Immunoglobulin Class Switching from Immunoglobulin M (IgM) to IgG and IgA is central to immunity against viruses and requires the activation of B cells by T cells via CD154 (CD40 ligand) and cytokines. These molecules limit their signaling activity in immune cells by turning on negative feedback proteins, including IκB and SOCS. We show here that negative factor (Nef) protein, an immunosuppressive human immunodeficiency virus 1 protein expressed and released by infected cells, penetrates B cells both in vivo and in vitro . Nef suppressed Immunoglobulin Class-switch DNA recombination by inducing IκBα and SOCS proteins, which blocked CD154 and cytokine signaling via NF-κB and STAT transcription factors. Thus, human immunodeficiency virus 1 may evade protective T cell–dependent IgG and IgA responses by 'hijacking' physiological feedback inhibitors in B cells via Nef.
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hiv 1 nef suppresses t cell dependent Immunoglobulin Class Switching by inducing inhibitors of cd40 and il 4 receptor signaling in bystander b cells
Blood, 2005Co-Authors: Andrea Cerutti, Daniel M Knowles, April Chiu, Amy Chadburn, Xugang QiaoAbstract:Background. Class switch DNA recombination (CSR) from IgM to IgG and IgA is central to immunity against pathogens and requires the activation of B cells by CD4 + T cells through CD40 ligand (CD40L) and cytokines, including IL-4 and IL-10. Viruses evade protective IgG and IgA responses through a number of strategies, including production of soluble proteins that suppress T cell-dependent (TD) Class Switching in bystander B cells. HIV-1 is thought to impair antigen-specific IgG and IgA production by inducing progressive depletion of CD4 + T cells. Although important, this mechanism is not sufficient to explain the intrinsically poor response of B cells from viremic patients to CD4 + T cell help. This prompted us to explore the B cell-modulating activity of negative factor (Nef), an early HIV-1 protein implicated in immunosuppression. Nef is released in the extracellular environment by infected cells and might perturb the function of bystander B cells by targeting them through its N-terminal myristoylated domain. Methods. Tonsillar tissue sections from healthy donors and lymph nodal tissue sections from 10 HIV-1-infected patients were analyzed for IgD, p24, and Nef expression by immunohistochemistry. Nef expression was also analyzed in IgD + B cells purified from healthy donors and exposed to a recombinant myristoylated or non-myristoylated Nef protein. These IgD+ B cells as well as an IgD + B cell line expressing a wild-type Nef transgene or a mutant Nef transgene lacking the myristoylated domain were utilized in CSR assays after further exposure to CD40L, IL-4 and IL-10. CSR and signaling were studied as described 1 , 2 , 3 . Results. We found that HIV-1-infected lymphoid follicles express large amounts of Nef. This viral protein penetrates in bystander B cells both in vivo and in vitro and interferes with the initiation of CSR by CD40L and cytokines without down-regulating CD40 and cytokine receptor expression on B cells. Rather, Nef up-regulates inhibitor of NF-κ B (Iκ B) and suppressor of cytokine signaling (SOCS) proteins, including SOCS1 and SOCS3, in B cells. These powerful inhibitory proteins attenuate the transcriptional activation of germline Ig gene promoters by blocking CD40 and cytokine receptor signaling through NF-κ B and signal transducer and activator of transcription (STAT), respectively. In addition, Nef hampers the up-regulation of key components of the CSR machinery, such as activation-induced cytidine deaminase (AID), and blocks the induction of IgG, IgA and IgE secretion by CD40L and cytokines. Under similar conditions, Nef spares B cell survival, B cell proliferation as well as B cell signaling through mitogen-activated protein kinase p38 and B cell-specific activation protein (BSAP or Pax5). Conclusions. Our findings suggest that HIV-1 inhibits IgG and IgA production not only by impairing CD4 + T cells, but also by turning on powerful CSR inhibitory pathways in bystander B cells through Nef. We propose that Nef-blocking agents might improve protective antibody responses to pathogens and vaccines in HIV-1-infected patients.
Janet Stavnezer - One of the best experts on this subject based on the ideXlab platform.
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mapping of switch recombination junctions a tool for studying dna repair pathways during Immunoglobulin Class Switching
Advances in Immunology, 2010Co-Authors: Janet Stavnezer, Andrea Bjorkman, Alberto Cagigi, Qiang PanhammarstromAbstract:Class switch recombination (CSR) is induced upon B cell activation and occurs within special DNA regions, termed switch (S) regions, which consist of tandem repeats of G-rich sequences. CSR occurs by introduction of double-strand breaks (DSBs) into each S region, and recombination by nonhomologous end-joining (NHEJ). The recombination event occurs during the G1 phase of the cell cycle in cells that are rapidly dividing. By examination of patients and mouse knock-out strains lacking various DNA-damage response factors and enzymes involved in DNA repair, much has been learned about which factors are important for CSR, how DSBs are introduced into S regions, and how the donor and acceptor S regions are then recombined. One of the approaches for analyzing the steps involved in CSR is to determine the nucleotide sequence of S-S junctions. Many of the DNA repair deficiencies alter the sequence of the recombination junctions, generally increasing the use of microhomologies, interpreted as a shift from Classical (C)-NHEJ to alternative end-joining (A-EJ). However, it is clear that A-EJ, is not simply one pathway; rather, recombination is likely to occur using various subsets of end-joining factors, which will vary depending on the structure of the DSBs provided by the initial phases of CSR. Herein we review the results of analyses of S-S junctions, suggest minimal information required for these analyses, and attempt to integrate these results in order to increase our understanding of the complex process of CSR.
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deletion of the nucleotide excision repair gene ercc1 reduces Immunoglobulin Class Switching and alters mutations near switch recombination junctions
Journal of Experimental Medicine, 2004Co-Authors: Carol E Schrader, Joycelyn Vardo, Erin K Linehan, Michael Z Twarog, Laura J Niedernhofer, Jan H J Hoeijmakers, Janet StavnezerAbstract:The structure-specific endonuclease ERCC1-XPF is an essential component of the nucleotide excision DNA repair pathway. ERCC1-XPF nicks double-stranded DNA immediately adjacent to 3' single-strand regions. Substrates include DNA bubbles and flaps. Furthermore, ERCC1 interacts with Msh2, a mismatch repair (MMR) protein involved in Class switch recombination (CSR). Therefore, ERCC1-XPF has abilities that might be useful for antibody CSR. We tested whether ERCC1 is involved in CSR and found that Ercc1(-)(/)(-) splenic B cells show moderately reduced CSR in vitro, demonstrating that ERCC1-XPF participates in, but is not required for, CSR. To investigate the role of ERCC1 in CSR, the nucleotide sequences of switch (S) regions were determined. The mutation frequency in germline Smicro segments and recombined Smicro-Sgamma3 segments cloned from Ercc1(-)(/)(-) splenic B cells induced to switch in culture was identical to that of wild-type (WT) littermates. However, Ercc1(-)(/)(-) cells show increased targeting of the mutations to G:C bp in RGYW/WRCY hotspots and mutations occur at sites more distant from the S-S junctions compared with WT mice. The results indicate that ERCC1 is not epistatic with MMR and suggest that ERCC1 might be involved in processing or repair of DNA lesions in S regions during CSR.
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role for mismatch repair proteins msh2 mlh1 and pms2 in Immunoglobulin Class Switching shown by sequence analysis of recombination junctions
Journal of Experimental Medicine, 2002Co-Authors: Carol E Schrader, Joycelyn Vardo, Janet StavnezerAbstract:B cells from mice deficient in mismatch repair (MMR) proteins show decreased ability to undergo Class switch recombination in vitro and in vivo. The deficit is not accompanied by any reduction in cell viability or alterations in the cell cycle in B cells cultured in vitro. To assess the role of MMR in Switching we examined the nucleotide sequences of Sμ-Sγ3 recombination junctions in splenic B cells induced in culture to switch to IgG3. The data demonstrate clear differences in the sequences of switch junctions in wild-type B cells in comparison with Msh2-, Mlh1-, and Pms2-deficient B cells. Sequences of switch junctions from Msh2-deficient cells showed decreased lengths of microhomology between Sμ and Sγ3 relative to junctions from wild-type cells and an increase in insertions, i.e., nucleotides which do not appear to be derived from either the Sμ or Sγ3 parental sequence. By contrast, 23% of junctions from Mlh1- and Pms2-deficient cells occurred at unusually long stretches of microhomology. The data indicate that MMR proteins are directly involved in Class Switching and that the role of Msh2 differs from that of Mlh1 and Pms2.
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Immunoglobulin Class Switching
Current Opinion in Immunology, 1996Co-Authors: Janet StavnezerAbstract:Antibody Class Switching is induced by B-cell activators in the presence of cytokines. The identity of the heavy-chain Class to which a B cell is switched is regulated by cytokines and B-cell activators at the level of transcription of unrearranged heavy chain constant genes. Gene-targeting experiments in mice have proved the essential role of these transcripts in switch recombination. Their possible functions are discussed in the context of a model for the mechanisms of Class Switching.
