Localization of the endogenous cysteine proteinase inhibitor, cystatin C, and the cysteine proteinase, cathepsin B, to the junctional epithelium in rat gingiva

The junctional epithelium (JE) is a primary site of defense against periodontal pathogens. Cystatin C is an endogenous inhibitor of cysteine proteinases such as cathepsin B and also has antibacterial actions against periodontal pathogens. However, the distribution and role of cystatin C in JE have not been clarified. To investigate the function of cystatin C in the host defense at dentogingival junction, we examined the immunolocalization of cystatin C and cathepsin B in rat gingiva using light and electron microscopy. The JE (particularly the coronal portion) was immunopositive for cystatin C, and immunoelectron microscopy revealed that cystatin C was localized to the vesicular, granular, and vacuolar compartments of JE cells. The pattern of cathepsin B immunoreactivity in JE cells resembled that of cystatin C. Both cystatin C and cathepsin B appeared to be localized to endosomal/lysosomal compartments within JE cells. These findings suggest that cystatin C regulates cysteine proteinase activity and exerts antibacterial effects both in the lysosomal compartments of JE cells and in the intercellular spaces of the JE. Cystatin C is thus able to participate in host defense against periodontal pathogens at the dentogingival junction.