Abstract
IL-4 and 8-mercaptoguanosine (8-SGuo) stimulation of CD38-activated B cells induces mu to gamma1 class switch recombination (CSR) at the DNA level leading to a high level of IgG1 production. Although some of signaling events initiated by IL-4 in activated B cells have been characterized, the involvement of TLR/MyD88 and Btk pathway in IL-4-dependent mu to gamma1 CSR has not been thoroughly evaluated. In this study, we characterized receptors for 8-SGuo and differential roles of 8-SGuo and IL-4 in the induction and mu to gamma1 CSR and IgG1 production. The role of TLR7 and MyD88 in 8-SGuo-induced AID expression and mu to gamma1 CSR was documented, as 8-SGuo did not act on CD38-stimulated splenic B cells from Tlr7(-/-) and Myd88(-/-) mice. CD38-activated B cells from Btk-deficient mice failed to respond to TLR7 ligands for the AID expression and CSR, indicating that Btk is also indispensable for the system. Stimulation of CD38-activated B cells with 8-SGuo induced significant AID expression and DNA double strand breaks, but IL-4 stimulation by itself did not trigger mu to gamma1 CSR. Intriguingly, the mu to gamma1 CSR in the B cells stimulated with CD38 and 8-SGuo totally depends on IL-4 stimulation. Similar results were obtained in the activated B cells through BCR and loxoribine, a well-known TLR7 ligand, in place of 8-SGuo. In vivo administration of TLR7 ligand and anti-CD38 antibody induced the generation of CD138(+) IgG1(+) cells. These results indicate that TLR7 is a receptor for 8-SGuo and plays an essential role in the AID and Blimp-1 expression; however it is not enough to complete mu to gamma1 CSR in CD38-activated B cells. IL-4 may be required for the induction of DNA repair system together with AID for the completion of CSR.
Publication types
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Research Support, Non-U.S. Gov't
MeSH terms
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ADP-ribosyl Cyclase 1 / immunology
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ADP-ribosyl Cyclase 1 / metabolism
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ADP-ribosyl Cyclase 1 / physiology*
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Animals
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Antibodies / pharmacology
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B-Lymphocytes / drug effects
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B-Lymphocytes / immunology*
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B-Lymphocytes / metabolism
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Cells, Cultured
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Cytidine Deaminase / genetics
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Cytidine Deaminase / metabolism
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Cytidine Deaminase / physiology
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Drug Synergism
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Guanosine / analogs & derivatives
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Guanosine / metabolism
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Guanosine / pharmacology
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Immunoglobulin Class Switching* / drug effects
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Immunoglobulin Class Switching* / genetics
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Immunoglobulin Class Switching* / physiology
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Immunoglobulin G / biosynthesis*
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Interleukin-4 / metabolism
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Interleukin-4 / pharmacology
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Interleukin-4 / physiology*
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Lymphocyte Activation* / drug effects
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Lymphocyte Activation* / genetics
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Membrane Glycoproteins / agonists
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Membrane Glycoproteins / genetics
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Membrane Glycoproteins / immunology
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Membrane Glycoproteins / metabolism
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Membrane Glycoproteins / physiology*
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Mice
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Mice, Inbred C57BL
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Mice, Transgenic
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Models, Biological
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Myeloid Differentiation Factor 88 / genetics
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Myeloid Differentiation Factor 88 / metabolism
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Myeloid Differentiation Factor 88 / physiology
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Positive Regulatory Domain I-Binding Factor 1
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Receptors, Antigen, B-Cell / metabolism
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Receptors, Antigen, B-Cell / physiology*
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Recombination, Genetic / drug effects
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Recombination, Genetic / immunology
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Toll-Like Receptor 7 / agonists
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Toll-Like Receptor 7 / genetics
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Toll-Like Receptor 7 / metabolism
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Toll-Like Receptor 7 / physiology*
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Transcription Factors / genetics
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Transcription Factors / metabolism
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Transcription Factors / physiology
Substances
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Antibodies
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Immunoglobulin G
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Membrane Glycoproteins
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Myd88 protein, mouse
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Myeloid Differentiation Factor 88
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Prdm1 protein, mouse
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Receptors, Antigen, B-Cell
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Tlr7 protein, mouse
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Toll-Like Receptor 7
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Transcription Factors
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Guanosine
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Interleukin-4
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loxoribine
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Positive Regulatory Domain I-Binding Factor 1
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Cd38 protein, mouse
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ADP-ribosyl Cyclase 1
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AICDA (activation-induced cytidine deaminase)
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Cytidine Deaminase