The present study was designed to investigate the expression of members of the toll-like receptor (TLR) family in human B cells. High-density, resting, and low-density activated tonsillar B cells expressed TLR9 and TLR10 mRNA transcripts at the highest levels. Expression was higher in activated B cells than in resting cells. Analysis of a range of resting and activated human leukocyte populations revealed that mRNA expression of TLR10 was restricted to B cells. Stimulation of resting B cells with anti-μ and anti-CD40 antibodies or with Staphylococcus aureus Cowan I bacteria (SAC) increased expression of TLR9 and TLR10. TLR1 and TLR4 expression were not significantly induced by B-cell activation. Interestingly, a CpG oligonucleotide, a TLR9 agonist, also stimulated TLR9 expression in B cells. Exposure to anti-μ antibodies augmented TLR9 expression, concomitantly and dramatically increasing the responsiveness of B cells to CpG oligonucleotides in terms of proliferation and chemokine (CC chemokine ligand 3 [CCL3] and CCL22) production. Epstein-Barr virus (EBV)-transformed cell lines and other cell lines representative of mature B-cell neoplasias (Burkitt lymphoma follicular lymphoma, multiple myeloma) expressed TLR9 and/or TLR10, whereas pre-B cell lines were negative. These results show that normal and neoplastic human B lymphocytes express a distinct TLR repertoire including TLR9 and TLR10 and that expression is increased upon engagement of the antigen receptor complex or TLR9 itself. Regulated expression of selected TLRs in B cells is likely to play an important role in linking innate and adaptive immune responses in normal and pathologic conditions.
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