Salivary mucins in oral mucosal defense.

1. Salivary mucins are well recognized as an important factor in the preservation of the health of the oral cavity. These large glycoproteins play a major role in the formation of protective coatings covering tooth enamel and oral mucosa, which act as a dynamic functional barrier capable of modulating the untoward effects of oral environment, and are of significance to the processes occurring within the epithelial perimeter of mucosal defense. 2. Based on macromolecular characteristics, the mucins in saliva fall into high (> 1000 kDa) and low (200-300 kDa) molecular weight forms. The two forms, although differ with respect to bacterial clearance ability, display virtually identical carbohydrate chain make-up, ranging in size from 3 to 16 sugar units. 3. Of the two mucin forms, the low molecular weight form more efficient in bacterial aggregation, predominates in saliva and oral mucosal mucus coat of caries-resistant individuals, while the level of the high molecular weight form is higher in caries-susceptible subjects. The saliva of caries-resistant individuals also exhibits greater activity of protease capable of conversion of the high molecular weight mucin to the low molecular weight form. 4. The bacterial aggregating activity of salivary mucins appears to be associated with sulfomucins rather than sialomucins. While the removal of sialic acid causes only partial loss in mucin aggregating capacity, a complete loss in the bacterial aggregating activity occurs following mucin desulfation. 5. The mucins in oral mucosal mucus coat interact with the epithelial surfaces through specific membrane receptors. This interaction apparently involves the carbohydrate moiety of mucin molecule and may be rendered vulnerable to disruption by opportunistic bacteria colonizing the oral mucosa. 6. Salivary sulfo- and sialomucins actively participate in the modulation of the oral mucosal calcium channel activity through the inhibition of EGF-stimulated channel protein tyrosine phosphorylation. This function of salivary mucins is of paramount importance to mucosal calcium homeostasis.