The surface proteinase of Treponema denticola may mediate attachment of the bacteria to epithelial cells

Abstract

Attachment of Treponema denticola ATCC 35405 was studied using a new epithelial model consisting of cultured periodontal ligament epithelial cells. T. denticola bound rapidly but selectively to the epithelial cells. Even at a high concentration of 1 x 1011 bacteria/mL, 31% of the epithelial cells did not bind any treponemes in confluent cultures. However, some of the cells bound large numbers of spirochetes. In sparse cultures with migrating epithelial cells, higher amounts of T. denticola were bound than in confluent cultures. Electron microscopy showed direct contact of T. denticola and epithelial cell membranes without apparent preference in the adhesion sites in either of the cell types. Fibronectin and bovine serum albumin did not inhibit binding of T. denticola to the epithelial cells. In contrast, serum and fibrinogen markedly inhibited binding. Pretreatment of T. denticola with proteinase K, heating at 60°C or exposure to pH 3.2 inhibited the attachment by 30, 78 and 89%, respectively, suggesting that T. denticola proteins were involved in the attachment. Protease inhibitors, phenylmethylsulfonyl fluoride and p-chloromercuribenzoic acid that inhibited the chymotrypsin-like proteinase of T. denticola, also inhibited the attachment of the spirochetes to the epithelial cells. Purified chymotrypsin-like proteinase bound rapidly to the epithelial cells and specific antibodies against the proteinase inhibited attachment of the treponemes to the epithelial cells. The results suggest that the T. denticola surface-bound chymotrypsin-like proteinase is involved in the binding of the bacteria to epithelial cells.