Attachment of T. denticola strains ATCC 33520, ATCC 35405, B11 and Ny541 to a morphologically distinct population of rat palatal epithelial cells

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Abstract
In the present study an assay for the attachment of T. denticola to epithelial cells is described. An indirect immunohistochemical staining method, using two native polyclonal antisera, revealed dark-brown coloured spirochetes attached to rat palatal epithelial cell (RPE) monolayers. In addition, two morphologically distinct populations of RPE cells could be distinguished in the monolayers when using phase contrast microscopy. One minor population consisted of isolated rounded RPE cells that were lying on top of a confluent monolayer of flattened RPE cells. The rounded RPE cells were more receptive for the attachment of T. denticola than the flattened cells. The rounded RPE cells were evenly distributed over the monolayer, but the attachment of spirochetes to the rounded cells was greater at the edge than in the centre of the monolayers. The percentage of rounded RPE cells with attached spirochetes depended on the incubation time (optimum 6 h), temperature (optimum 37 degrees C) and pH (optimum 7.0). It is speculated that the attachment of T. denticola is a physical/chemical process of yet unknown nature and that differences in the number of microvilli and/or the amount of available receptors, between the two morphologically distinct cell types, accounts for the differences in the numbers of attached spirochetes.