Cell surface proteins SspA and SspB in Streptococcus gordonii and SpaP in Streptococcus mutans are members of the antigen I/II family of polypeptides produced by oral streptococci. These proteins are adhesins and mediate species-specific binding of cells to a variety of host and bacterial receptors. Here we show that antigen I/II polypeptides are involved in the attachment of oral streptococci to collagen and that they also determine the ability of these bacteria to invade human root dentinal tubules. Wild-type S. gordonii DL1 (Challis) cells showed heavy invasion of tubules to a depth of approximately 200 m, whereas the abilities of cells of isogenic mutant strains OB220 (sspA) and OB219 (sspA sspB) to invade were 50 and >90% reduced, respectively. Likewise, wild-type S. mutans NG8 cells invaded dentinal tubules, whereas cells of isogenic mutant strain 834 (spaP) did not. The invasive abilities of strains OB220 and OB219 were restored by heterologous expression of S. mutans SpaP polypeptide in these strains. The extents of tubule invasion by various wild-type and mutant strains correlated with their levels of adhesion to type I collagen, a major component of dentin. Furthermore, S. gordonii DL1 cells exhibited a growth response to collagen by forming long chains. This was not shown by ssp mutants but was restored by the expression of SpaP in these cells. The production of SspA polypeptide by S. gordonii DL1, but not production of SspB polypeptide by strain OB220 (sspA), was enhanced in the presence of collagen. These results are the first to demonstrate that antigen I/II family polypeptides bind collagen and mediate a morphological growth response of streptococci to collagen. These antigen I/II polypeptide activities are critical for intratubular growth of streptococci and thus for establishment of endodontic infections.

Cell wall-anchored polypeptides of the antigen I/II family are produced by many species of oral streptococci. These proteins mediate adhesion of streptococci to salivary glycoproteins and to other oral microorganisms and promote binding of cells to collagen type I and invasion of dentinal tubules. Since infections of the root canal system have a mixed anaerobic bacterial etiology, we investigated the hypothesis that coadhesion of anaerobic bacteria with streptococci may facilitate invasive endodontic disease. Porphyromonas gingivalis ATCC 33277 cells were able to invade dentinal tubules when cocultured with Streptococcus gordonii DL1 (Challis) but not when cocultured with Streptococcus mutans NG8. An isogenic noninvasive mutant of S. gordonii, with production of SspA and SspB (antigen I/II family) polypeptides abrogated, was deficient in binding to collagen and had a 40% reduced ability to support adhesion of P. gingivalis. Heterologous expression of the S. mutans SpaP (antigen I/II) protein in this mutant restored collagen binding and tubule invasion but not adhesion to P. gingivalis or the ability to promote P. gingivalis coinvasion of dentin. An isogenic afimbrial mutant of P. gingivalis had 50% reduced binding to S. gordonii cells but was unaffected in the ability to coinvade dentinal tubules with S. gordonii wild-type cells. Expression of the S. gordonii SspA or SspB polypeptide on the surface of Lactococcus lactis cells endowed these bacteria with the abilities to bind P. gingivalis, penetrate dentinal tubules, and promote P. gingivalis coinvasion of dentin. The results demonstrate that collagen-binding and P. gingivalis-binding properties of antigen I/II polypeptides are discrete functions. Specificity of antigen I/II polypeptide recognition accounts for the ability of P. gingivalis to coinvade dentinal tubules with S. gordonii but not with S. mutans. This provides evidence that the specificity of interbacterial coadhesion may influence directly the etiology of pulpal and periapical diseases.

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Mucosa from the hard and soft palates, molar gingiva, cheek and dorsal surface of the tongue of the rat was examined in the light microscope, following Mallory's triple connective tissue stain, and in the scanning and transmission electron microscopes. The epithelium covering the hard palate, gingiva, the smooth band of mucosa at the junction of the hard and soft palates, intermediate zones of the soft palate, fungiform papilla-like structures in the central zone of the soft palate, the fungiform papillae, and the more superficial part and posterior surfaces of the filiform papillae of the tongue all exhibited complete orthokeratinization. The oral surfaces of the epithelial cells in all these areas had a honeycomb pattern of interconnecting ridges surrounding depressions. Imprints of the overlying cells that had been desquamated were apparent, and the lateral boundaries between the cells were formed by two raised ridges separated by a gap. The epithelium covering the cheek, central zone of the soft palate apart from the fungiform papilla-like structures, lateral zones of the soft palate, gingival crevice, and the mucosa between the fungiform and filiform papillae of the tongue all exhibited incomplete orthokeratinization. The oral surfaces of the epithelial cells in all these areas were relatively smooth and did not exhibit a honeycomb pattern of interconnecting ridges. Imprints of the overlying cells that had been desquamated and the lateral boundaries between the cells were only very occasionally found. In the transmission electron microscope the outlines of the cells were compatible with the surface patterns seen in the scanning electron microscope. The possible relationships between the degree of orthokeratinization and ultrastructure of the various epithelia are discussed.