A distinct Toll‐like receptor repertoire in human tonsillar B cells, directly activated by Pam3CSK4, R‐837 and CpG‐2006 stimulation
ABSTRACT 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– (naïve 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 naïve, 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 Pam3CSK4, 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.
Article: Toll-like receptor expression and responsiveness of distinct murine splenic and mucosal B-cell subsets.[show abstract] [hide abstract]
ABSTRACT: Toll-like receptors (TLRs) are pattern recognition receptors that recognize pathogen associated molecular patterns and trigger innate immunity leading to initiation of adaptive immunity. TLR-mediated activation of dendritic cells (DCs) is known to be a critical event in the initiation of cellular and humoral immune responses. Recent work however suggests that B cells also express TLRs, and that they can be activated via TLR ligands. However, whether such B cell activation occurs only on memory B cells, or whether it can also occur on truly naïve B cells remains controversial. Furthermore, the expression and functional relevance of TLRs on distinct subsets of B cells, which are known to play differential roles in humoral responses is not known. In this study, we investigated the expression pattern of different TLRs in distinct subsets of murine B cells (naïve, memory, follicular, marginal zone, B-1 and peyer's patch). In contrast to the reported restricted expression pattern of TLRs in human peripheral blood naïve B cells, murine splenic naïve B cells express a variety of TLRs with the exception of TLR5 and 8. Consistent with this relatively broad expression pattern, murine naive B cells proliferate and secrete antibody to a variety of TLR agonists in vitro, in the absence of B-cell receptor cross-linking. In addition, we observed subtle differences in the antibody secretion pattern of follicular, marginal zone, B-1 and peyer's patch B-cell subsets. Thus various B cell subsets, including truly naïve B cells, express multiple TLRs, and signaling via such TLRs results in their robust proliferation and antibody secretion, even in the absence of dendritic cell activation, or T-cell help.PLoS ONE 02/2007; 2(9):e863. · 4.09 Impact Factor
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ABSTRACT: Secretion of outer membrane vesicles (OMV) is an intriguing phenomenon of Gram-negative bacteria and has been suggested to play a role as virulence factors. The respiratory pathogens Moraxella catarrhalis reside in tonsils adjacent to B cells, and we have previously shown that M. catarrhalis induce a T cell independent B cell response by the immunoglobulin (Ig) D-binding superantigen MID. Here we demonstrate that Moraxella are endocytosed and killed by human tonsillar B cells, whereas OMV have the potential to interact and activate B cells leading to bacterial rescue. The B cell response induced by OMV begins with IgD B cell receptor (BCR) clustering and Ca(2+) mobilization followed by BCR internalization. In addition to IgD BCR, TLR9 and TLR2 were found to colocalize in lipid raft motifs after exposure to OMV. Two components of the OMV, i.e., MID and unmethylated CpG-DNA motifs, were found to be critical for B cell activation. OMV containing MID bound to and activated tonsillar CD19(+) IgD(+) lymphocytes resulting in IL-6 and IgM production in addition to increased surface marker density (HLA-DR, CD45, CD64, and CD86), whereas MID-deficient OMV failed to induce B cell activation. DNA associated with OMV induced full B cell activation by signaling through TLR9. Importantly, this concept was verified in vivo, as OMV equipped with MID and DNA were found in a 9-year old patient suffering from Moraxella sinusitis. In conclusion, Moraxella avoid direct interaction with host B cells by redirecting the adaptive humoral immune response using its superantigen-bearing OMV as decoys.PLoS Pathogens 01/2010; 6(1):e1000724. · 9.13 Impact Factor