Bacterial fimbriae stimulate proinflammatory activation in the endothelium through distinct TLRs

The major and minor fimbriae proteins produced by the human pathogen Porphyromonas gingivalis are required for invasion of human aortic endothelial cells and for the stimulation of potent inflammatory responses. In this study, we report that native forms of both the major and minor fimbriae proteins bind to and signal through TLR2 for this response. Major and minor fimbriae bound to a human TLR2:Fc chimeric protein with an observed K(d) of 28.9 nM and 61.7 nM, respectively. Direct binding of the major and minor fimbriae to a human chimeric CD14-Fc protein also established specific binding of the major and minor fimbriae to CD14 with classic saturation kinetics. Using a P. gingivalis major and minor fimbriae mutant, we confirmed that TLR2 binding in whole cells is dependent on the expression of the major and minor fimbriae. Although we did not observe binding with the major or minor fimbriae to the TLR4-Fc chimeric protein, signaling through TLR4 for both proteins was demonstrated in human embryonic kidney 293 cells transfected with TLR4 and only in the presence MD-2. Transient transfection of dominant-negative forms of TLR2 or TLR4 reduced IL-8 production by human aortic endothelial cells following stimulation with major or minor fimbriae. The ability of two well-defined microbe-associated molecular patterns to select for innate immune recognition receptors based on accessory proteins may provide a novel way for a pathogen to sense and signal in appropriate host environments.