title: B cell TLR1/2, TLR4, TLR7 and TLR9 interact in induction of class switch DNA recombination: modulation by BCR and CD40, and relevance to T-independent antibody responses.
abstract: Ig class switch DNA recombination (CSR) in B cells is crucial to the maturation of antibody responses. It requires IgH germline IH-CH transcription and expression of AID, both of which are induced by engagement of CD40 or dual engagement of a Toll-like receptor (TLR) and B cell receptor (BCR). Here, we have addressed cross-regulation between two different TLRs or between a TLR and CD40 in CSR induction by using a B cell stimulation system involving lipopolysaccharides (LPS). LPS-mediated long-term primary class-switched antibody responses and memory-like antibody responses in vivo and induced generation of class-switched B cells and plasma cells in vitro. Consistent with the requirement for dual TLR and BCR engagement in CSR induction, LPS, which engages TLR4 through its lipid A moiety, triggered cytosolic Ca2+ flux in B cells through its BCR-engaging polysaccharidic moiety. In the presence of BCR crosslinking, LPS synergized with a TLR1/2 ligand (Pam3CSK4) in CSR induction, but much less efficiently with a TLR7 (R-848) or TLR9 (CpG) ligand. In the absence of BCR crosslinking, R-848 and CpG, which per se induced marginal CSR, virtually abrogated CSR to IgG1, IgG2a, IgG2b, IgG3 and/or IgA, as induced by LPS or CD154 (CD40 ligand) plus IL-4, IFN-γ or TGF-β, and reduced secretion of class-switched Igs, without affecting B cell proliferation or IgM expression. The CSR inhibition by TLR9 was associated with the reduction in AID expression and/or IgH germline IH-S-CH transcription, and required co-stimulation of B cells by CpG with LPS or CD154. Unexpectedly, B cells also failed to undergo CSR or plasma cell differentiation when co-stimulated by LPS and CD154. Overall, by addressing the interaction of TLR1/2, TLR4, TLR7 and TLR9 in the induction of CSR and modulation of TLR-dependent CSR by BCR and CD40, our study suggests the complexity of how different stimuli cross-regulate an important B cell differentiation process and an important role of TLRs in inducing effective T-independent antibody responses to microbial pathogens, allergens and vaccines.
authors.affiliation: Institute for Immunology, University of California , Irvine, CA , USA .
authors.forename: Egest J
authors.initials: EJ
authors.lastname: Pone
authors.forename: Zheng
authors.initials: Z
authors.lastname: Lou
authors.forename: Tonika
authors.initials: T
authors.lastname: Lam
authors.forename: Milton L
authors.initials: ML
authors.lastname: Greenberg
authors.forename: Rui
authors.initials: R
authors.lastname: Wang
authors.forename: Zhenming
authors.initials: Z
authors.lastname: Xu
authors.forename: Paolo
authors.initials: P
authors.lastname: Casali
mesh_terms: D000818:Animals; D001402:B-Lymphocytes / Q000166:cytology / Q000187:drug effects / Q000276:immunology; D019013:CD40 Antigens / Q000235:genetics / Q000276:immunology*; D023201:CD40 Ligand / Q000494:pharmacology; D002118:Calcium / Q000276:immunology / Q000378:metabolism; D002454:Cell Differentiation; D016207:Cytokines / Q000096:biosynthesis; D005786:Gene Expression Regulation / Q000276:immunology; D007093:Imidazoles / Q000494:pharmacology; D017578:Immunoglobulin Class Switching / Q000187:drug effects; D007074:Immunoglobulin G / Q000096:biosynthesis* / Q000145:classification; D055666:Lipopeptides / Q000494:pharmacology; D008070:Lipopolysaccharides / Q000494:pharmacology; D008562:Membrane Glycoproteins / Q000235:genetics / Q000276:immunology*; D051379:Mice; D008810:Mice, Inbred C57BL; D020239:Receptor Cross-Talk / Q000276:immunology; D011947:Receptors, Antigen, B-Cell / Q000235:genetics / Q000276:immunology*; D011995:Recombination, Genetic; D015398:Signal Transduction; D051194:Toll-Like Receptor 1 / Q000235:genetics / Q000276:immunology*; D051195:Toll-Like Receptor 2 / Q000235:genetics / Q000276:immunology*; D051197:Toll-Like Receptor 4 / Q000235:genetics / Q000276:immunology*; D051199:Toll-Like Receptor 7 / Q000235:genetics / Q000276:immunology*; D051217:Toll-Like Receptor 9 / Q000235:genetics / Q000276:immunology*
chemical_list: D019013:CD40 Antigens; D016207:Cytokines; D007093:Imidazoles; D007074:Immunoglobulin G; D055666:Lipopeptides; D008070:Lipopolysaccharides; D008562:Membrane Glycoproteins; C508075:Pam(3)CSK(4) peptide; D011947:Receptors, Antigen, B-Cell; C493486:Tlr2 protein, mouse; C493487:Tlr4 protein, mouse; C477038:Tlr7 protein, mouse; C495370:Tlr9 protein, mouse; D051194:Toll-Like Receptor 1; D051195:Toll-Like Receptor 2; D051197:Toll-Like Receptor 4; D051199:Toll-Like Receptor 7; D051217:Toll-Like Receptor 9; D023201:CD40 Ligand; D002118:Calcium; C402365:resiquimod
keywords: Antibody; B cell receptor; B cells; CpG; T-independent antibody response; Toll-like receptor; class switch DNA recombination; lipopolysaccharides