Species-specific PAMP recognition by TLR2 and evidence for species-restricted interaction with Dectin-1

The TLR2 response depends on the ECD of a species, not the ICD, and is modulated by interaction with different innate immune receptors. TLRs mediate recognition of a wide range of microbial products, including LPS, lipoproteins, flagellin, and bacterial DNA, and signaling through TLRs leads to the production of inflammatory mediators. In addition to TLRs, many other surface receptors have been proposed to participate in innate immunity and microbial recognition, and signaling through some of these, for example, C-type lectins, is likely to cooperate with TLR signaling in defining inflammatory responses. In the present study, we examined the importance of the ECD and intracellular TIR domain of boTLR2 and huTLR2 to induce a species-specific response by creating a chimeric TLR2 protein. Our results indicate that the strength of the response to any TLR2 ligand tested was dependent on the extracellular, solenoid structure, but not the intracellular TIR domain. Furthermore, we examined whether the recognition of two PAMPs by Dectin-1, a CLR, depends on the interaction with TLR2 from the same species. TLR2 expression seemed to affect the Dectin-1-dependent production of CXCL8 to -glucan containing zymosan as well as Listeria monocytogenes. Furthermore, the interaction of Dectin-1 with TLR2 seemed to require that both receptors are from the same species. Our data demonstrate that the differences in the TLR2 response seen between the bovine and human system depend on the ECD of TLR2 and that collaborative recognition of distinct microbial components by different classes of innate-immune receptors is crucial in orchestrating inflammatory responses.