Objectives: To elucidate the role of the innate immune receptor Toll-Like receptor 2 (TLR2) in the in vivo response to challenge with live
Porphyromonas gingivalis (
P. gingivalis).Methods: Titanium chambers were placed subcutaneously in wild-type and TLR2 deficient mice. Ten days following placement chambers were seeded with
P. gingivalis and then sampled at various time points for determination of bacterial survival and the host immune response. Results: Prior to bacterial challenge, chamber cells express high levels of the leukocyte marker CD45. At 2 hours following challenge the expression of CD45 is significantly down-regulated in wild-type (wt) mice, a phenomenon known to correlate with cell activation. In TLR2 deficient mice, however, cells continue to express high levels of CD45 suggesting that they are not activated. Analysis of cytokines at 2 hours revealed high levels of TNFα and IL-1ß in wt mice whereas no TNFα and only slight IL1ß were detected in TLR2 deficient mice, again suggesting that TLR2 is necessary for rapid and potent activation in response to
P. gingivalis. We next tested the contribution of TLR2 to
P. gingivalis clearance. Chamber fluid recovered 2 and 24 hours post-injection was plated and grown under anaerobic conditions. At 2 hours we recovered
P. gingivalis colonies from wt mice in equal CFUs to the inoculum, and at 24 hours there was only a slight decrease in CFUs. Unexpectedly, bacterial clearance was enhanced in TLR2 deficient mice: at 2 hours CFUs were reduced by several orders of magnitude and at 24 hours no
P. gingivalis colonies were recovered.Conclusions: We have made the novel discovery that the TLR2-mediated response to P. gingivalis protects the bacteria from rapid clearance despite activated cells and the presence of abundant pro-inflammatory cytokines.