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Updated: May 11, 2026

Generation of Human CD40-activated B cells
Published on: October 17, 2009
Toll-like receptor 9, transmembrane activator and calcium-modulating cyclophilin ligand interactor, and CD40
Esra Ozcan1, Ingrid Rauter, Lilit Garibyan
1Division of Immunology, Children's Hospital, Harvard Medical School, Boston, MA 02115, USA.
Background:
B cells receive activating signals from T cells through CD40, from microbial DNA through Toll-like receptor (TLR) 9, and from dendritic cells through transmembrane activator and calcium-modulating cyclophilin ligand interactor (TACI). TLR9 and CD40 ligation augment TACI-driven B-cell activation, but only the mechanism of synergy between CD40 and TACI has been explored. Synergy between CD40 and TLR9 in B-cell activation is controversial.
Objective:
We sought to examine the mechanisms by which TLR9 modulates CD40- and TACI-mediated activation of B cells and to determine whether all 3 receptors synergize to activate B cells.
Methods:
Naive murine B cells and human PBMCs were stimulated with combinations of anti-CD40, CpG, and a proliferation inducing ligand in the presence of IL-4. Proliferation was measured by means of tritiated thymidine incorporation. Immunoglobulin production was measured by means of ELISA. Class-switch recombination (CSR) was examined by measuring mRNA for germline transcripts, activation-induced cytidine deaminase (AICDA), and mature immunoglobulin transcripts. Plasma cell differentiation was examined by using syndecan-1/CD138 staining and mRNA expression of B lymphocyte-induced maturation protein 1 (Blimp-1).
Results:
TLR9 synergized with CD40 and TACI in driving CSR and inducing IgG(1) and IgE secretion by naive murine B cells and synergized with TACI in driving B-cell proliferation and plasma cell differentiation. All 3 receptors synergized together in driving murine B-cell proliferation, CSR, plasma cell differentiation, and IgG(1) and IgE secretion. TLR9 synergized with CD40 and TACI in driving IgG secretion in IL-4-stimulated human B cells.
Conclusion:
Signals from TLR9, TACI, and CD40 are integrated to promote B-cell activation and differentiation.
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