Treponema lecithinolyticum is known to be associated with rapidly progressive periodontitis. The full-length gene encoding the major surface protein MspTL of this organism was cloned and expressed by using the expression vector pQE30. Recombinant MspTL (rMspTL) protein was purified and functionally characterized. MspTL was one of several T lecithinolyticum surface proteins that bound to cultured human gingival fibroblasts (HGFs). As well, it strongly induced IL-6 production by HGFs. These observations suggest that MspTL contributes to pathogenesis of periodontitis by adhesion to host cells and by induction of the proinflammatory cytokine IL-6.