Toll-like receptor-9 triggering modulates expression of α-4 integrin on human B lymphocytes and their adhesion to...

The interaction of human B lymphocytes as recirculating cells with their microenvironment components including fibronectin is an instrumental process that directs their further responses in an inflammatory milieu or during their development in secondary lymphoid organs. Factors derived from extracellular environment, including those of pathogens, termed pathogen-associated molecular patterns, may have effects on this interaction, yet no study to date has addressed these effects. In this study, we explored the effect of Toll-like receptor 9 (TLR9) triggering on the interaction of normal B cells with fibronectin and collagen.

The synthetic analog of TLR9 ligand, CpG-C, was used for stimulating the cells. The expression pattern of very late antigen-4 integrin was studied by fluorescence-activated cell sorting and Western blotting experiments, and cell adhesion was analyzed by fluorometric adhesion assay.

CpG at 0.5 μM upregulated fibronectin receptor (very late antigen-4) expression and cell adhesion, and increasing the CpG concentration did not have further effect. Blocking experiments with TLR9 signaling inhibitor, TTAGGG, anti-α4 antibody, and IκBα phosphorylation inhibitor, Bay 11-7082, confirmed that the CpG-induced induction level was TLR9 (partly), very late antigen-4, and nuclear factor-κB-mediated, respectively.

This study indicates that TLR9 triggering on B cells influences their interaction with extracellular matrix, which will be critical in modulating activation of these cells in conditions, such as infections, and gives a basic insight into the contribution of innate immunity elements in B-cell functional responses.