A distinct Toll-like receptor repertoire in human tonsillar B cells, directly activated by Pam3CSK4, R-837 and CpG-2006 stimulation

Toll-like receptors (TLRs) recognize specific pathogen-associated molecular patterns (PAMPs), which subsequently trigger innate immunity. Recent data also suggest a role for TLRs in the direct activation of adaptive immune cells. In the present study, the expression and function of TLR1-TLR10 were characterized in purified human tonsillar B cells, focusing on differences among CD19(+) CD38(-) CD27(-) (naive B cells), CD19(+) IgD(-) CD27- [germinal centre (GC) B cells] and CD19(+) CD38(-)CD27(+) (memory B cells) cells. The study was also designed to compare the TLR expression in B cells obtained from infected and hyperplastic tonsils that served as controls. The results demonstrated a distinct repertoire of TLRs, in which TLR1, TLR2, TLR7, TLR9 and TLR10 predominated. No differences were found among naive, GC and memory B cells. Tonsillar infection did not substantially alter the TLR expression profile in ex vivo-isolated B-cell subsets. Purified CD19+ B cells stimulated with Pam(3)CSK(4), R-837 and CpG oligodeoxynucleotide (ODN) 2006, via TLR1/TLR2, TLR7 and TLR9, respectively, showed an induction of interleukin-6 secretion and an up-regulated expression of human leucocyte antigen (HLA)-DR. Collectively, the present study demonstrates that B cells exhibit constitutively high levels of specific TLRs, which are not developmentally regulated during the B-cell differentiation process. Ongoing microbial infections, such as chronic tonsillitis, do not appear to affect the TLR profile in B cells. Furthermore, the distinct expression of TLRs allows B cells to.respond directly to the cognate PAMPs. This further emphasizes the role of TLRs in directly activating adaptive immune cells.