Cellular Microbiology (2006) 8(10), 1557–1570 doi:10.1111/j.1462-5822.2006.00730.x First published online 2 May 2006 © 2006 The Authors Journal compilation © 2006 Blackwell Publishing Ltd Blackwell Publishing LtdOxford, UKCMICellular Microbiology 1462-5814© 2006 The Authors; Journal compilation © 2006 Blackwell Publishing Ltd ? 200681015571570Original ArticlePorphyromonas gingivalis interactions with TLR2 and core- ceptorsG. Hajishengallis et al. Received 1 February, 2006; revised 9 March, 2006; accepted 12 March, 2006. *For correspondence. E-mail g0haji01@louisville.edu; Tel. (+1) 502 852 5276; Fax (+1) 502 852 4052. Differential interactions of fimbriae and lipopolysaccharide from Porphyromonas gingivalis with the Toll-like receptor 2-centred pattern recognition apparatus George Hajishengallis, 1,2 * Richard I. Tapping, 3 Evlambia Harokopakis, 1,4 So-ichiro Nishiyama, 5 Pukar Ratti, 6 Robert E. Schifferle, 7 Elizabeth A. Lyle, 3 Martha Triantafilou, 8 Kathy Triantafilou 8 and Fuminobu Yoshimura 5 1 Center for Oral Health and Systemic Disease and Departments of 2 Periodontics/Endodontics and 4 Orthodontics/Pedodontics, University of Louisville Health Sciences Center, Louisville, KY 40292, USA. 3 Department of Microbiology, University of Illinois, Urbana, IL 61801, USA. 5 Department of Microbiology, School of Dentistry, Aichi- Gakuin University, Nagoya 464-8650, Japan. 6 Department of Microbiology and Immunology, LSU Health Sciences Center, New Orleans, LA 70119, USA. 7 Department of Oral Biology, University at Buffalo, NY 14214, USA. 8 Infection and Immunity Group, School of Life Sciences, University of Sussex, Falmer, Brighton, BN1 9QG, UK. Summary The lipopolysaccharide (LPS) and fimbriae of Porphy- romonas gingivalis play important roles in periodon- tal inflammation and pathogenesis. We investigated fimbriae and LPS from several P. gingivalis strains in terms of relative dependence on Toll-like receptor (TLR) signalling partners or accessory pattern- recognition molecules mediating ligand transfer to TLRs, and determined induced assembly of receptor complexes in lipid rafts. Fimbriae could utilize TLR1 or TLR6 for cooperative TLR2-dependent activation of transfected cell lines, in contrast to LPS and a mutant version of fimbriae which displayed preference for TLR1. Whether used to activate human cell lines or mouse macrophages, fimbriae exhibited strong dependence on membrane-expressed CD14 (mCD14), which could not be substituted for by soluble CD14 (sCD14). In contrast, sCD14 efficiently substituted for mCD14 in LPS-induced cellular activation. LPS- binding protein was more important for LPS- than for fimbria-induced cell activation, whereas the con- verse was true for CD11b/CD18. Cell activation by LPS or fimbriae required lipid raft function and formation of heterotypic receptor complexes (TLR1-2/CD14/ CD11b/CD18), although wild-type fimbriae addition- ally recruited TLR6. In summary, TLR2 activation by P. gingivalis LPS or fimbriae involves differential dependence on accessory signalling or ligand- binding receptors, which may differentially influence innate immune responses. Introduction Porphyromonas gingivalis is an anaerobic Gram-negative oral bacterium which is strongly associated with periodon- tal disease and implicated as a contributory factor in the development of atherosclerosis (Zambon et al ., 1994; Chun et al ., 2005; Desvarieux et al ., 2005). This pathogen expresses adhesive filamentous appendages on its cell surface, known as fimbriae, which constitute a major P. gingivalis virulence factor on the basis of studies in animal models of periodontitis or atherosclerosis (Malek et al ., 1994; Gibson et al ., 2004). Another widely studied surface structure of P. gingivalis is its lipopolysaccharide (LPS), which, however, displays significant structural and biological differences from the prototypical LPS of enteric bacteria (Dixon and Darveau, 2005). Both P. gingivalis LPS (PgLPS) and fimbriae are detected by pattern- recognition receptors (PRRs) of the innate immune sys- tem resulting in host cell activation (Hajishengallis et al ., 2002; Ogawa et al ., 2002; Darveau et al ., 2004; Hajishen- gallis et al ., 2005a; Zhou et al ., 2005). Lipopolysaccharide is a classical example of a pathogen-associated molecular pattern (PAMP), i.e. the recognition substrate of PRRs such as the Toll-like recep- tors (TLRs) (Medzhitov, 2001; Akira and Takeda, 2004). The relatively conserved structure of PAMPs renders them ideal targets for detection by the similarly conserved PRRs (Medzhitov, 2001). On the other hand, virulence factors (e.g. protein adhesins) are responsible for micro- bial adaptation within a particular host environment and