title: TLR4 promotes B cell maturation: independence and cooperation with B lymphocyte-activating factor.
abstract: We have previously shown that TLR4 triggering promotes the generation of CD23(+)CD93(+) transitional T2-like cells in vitro from mouse B cell precursors, suggesting a possible role for this receptor in B cell maturation. In this study, we perform an extensive study of cell surface markers and functional properties of B cells matured in vitro with LPS, comparatively with the well-known B cell maturation factor B lymphocyte-activating factor (BAFF). LPS increased generation of CD23(+) transitional B cells in a TLR4-dependent way, upregulating IgD and CD21 and downregulating CD93, without inducing cell proliferation, in a manner essentially equivalent to BAFF. For both BAFF and LPS, functional maturation of the IgM(+)CD23(+)CD93(+) cells was confirmed by their higher proliferative response to anti-CD40 plus IL-4 compared with IgM(+)CD23(neg)CD93(+) cells. BAFF-R-Fc-mediated neutralization experiments showed that TLR4-induced B cell maturation was independent of BAFF. Distinct from BAFF, maturation by LPS relied on the activation of canonical NF-kappaB pathway, and the two factors together had complementary effects, leading to higher numbers of IgM(+)CD23(+)CD93(+) cells with their simultaneous addition. Importantly, BCR cross-linking abrogated the generation of CD23(+) B cells by LPS or BAFF, indicating that signals mimicking central tolerance act on both systems. Addition of cyclosporin A reverted BCR-mediated inhibition, both for BAFF and LPS, suggesting similar regulation of signaling pathways by calcineurin. Finally, LPS-injected mice showed a rapid increase of mature B cells in the bone marrow, suggesting that TLR4 signaling may effectively stimulate B cell maturation in vivo, acting as an accessory stimulus in B cell development, complementary to the BAFF physiological pathway.
authors.affiliation: Department of Immunology, Institute of Microbiology, Federal University of Rio de Janeiro, Brazil.
authors.forename: Elize A
authors.initials: EA
authors.lastname: Hayashi
authors.forename: Alessandra
authors.initials: A
authors.lastname: Granato
authors.forename: Luciana S
authors.initials: LS
authors.lastname: Paiva
authors.forename: Alvaro L
authors.initials: AL
authors.lastname: Bertho
authors.forename: Maria
authors.initials: M
authors.lastname: Bellio
authors.forename: Alberto
authors.initials: A
authors.lastname: Nobrega
mesh_terms: D000818:Animals; D053264:B-Cell Activating Factor / Q000502:physiology*; D016175:B-Lymphocyte Subsets / Q000166:cytology / Q000276:immunology* / Q000378:metabolism*; D002454:Cell Differentiation / Q000276:immunology*; D049109:Cell Proliferation; D002478:Cells, Cultured; D018920:Coculture Techniques; D008070:Lipopolysaccharides / Q000502:physiology; D008211:Lymphocyte Cooperation / Q000276:immunology*; D051379:Mice; D008810:Mice, Inbred C57BL; D017455:Receptors, IgE / Q000096:biosynthesis; D015398:Signal Transduction / Q000276:immunology; D051197:Toll-Like Receptor 4 / Q000502:physiology*
chemical_list: D053264:B-Cell Activating Factor; D008070:Lipopolysaccharides; D017455:Receptors, IgE; C493487:Tlr4 protein, mouse; D051197:Toll-Like Receptor 4