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TLR4 promotes B cell maturation: independence and cooperation with B lymphocyte-activating factor
Elize A Hayashi1, Alessandra Granato, Luciana S Paiva
1Department of Immunology, Institute of Microbiology, Federal University of Rio de Janeiro, Brazil.
Journal of Immunology (Baltimore, Md. : 1950)
|April 2, 2010
Summary
Toll-like receptor 4 (TLR4) activation by LPS promotes B cell maturation similarly to BAFF, acting as an accessory signal in vivo. This TLR4-induced maturation is independent of BAFF but relies on NF-kappaB signaling and is inhibited by BCR cross-linking.
Area of Science:
- Immunology
- Cell Biology
- Molecular Biology
Background:
- Toll-like receptor 4 (TLR4) is implicated in B cell maturation.
- B lymphocyte-activating factor (BAFF) is a known B cell maturation factor.
- Understanding accessory signals in B cell development is crucial.
Purpose of the Study:
- To extensively study B cell maturation induced by LPS via TLR4.
- To compare LPS-induced maturation with BAFF-mediated maturation.
- To elucidate the signaling pathways and regulatory mechanisms involved.
Main Methods:
- In vitro culture of mouse B cell precursors with LPS and BAFF.
- Analysis of cell surface markers (CD23, CD93, IgD, CD21, IgM) by flow cytometry.
- Functional assays including proliferative responses and neutralization experiments (BAFF-R-Fc).
- Investigation of signaling pathways (NF-kappaB, calcineurin) and B cell receptor (BCR) cross-linking effects.
- In vivo studies with LPS-injected mice.
Main Results:
- LPS, via TLR4, induced CD23(+) transitional B cell generation, upregulating IgD and CD21 while downregulating CD93, similar to BAFF but without proliferation.
- TLR4-induced maturation was BAFF-independent and involved canonical NF-kappaB activation; simultaneous addition of LPS and BAFF showed complementary effects.
- BCR cross-linking abrogated LPS- and BAFF-induced CD23(+) B cell generation, an effect reversed by cyclosporin A, suggesting calcineurin involvement.
- LPS injection in mice rapidly increased mature B cells in bone marrow.
Conclusions:
- TLR4 signaling acts as an accessory stimulus for B cell maturation in vivo, complementing the BAFF pathway.
- LPS-induced B cell maturation involves NF-kappaB activation and is regulated by BCR signaling and calcineurin.
- TLR4 provides a distinct but complementary pathway to BAFF for promoting B cell development.
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