It is thought to play an immune role in the junctional epithelium at the gingival crevice in the human mouth.

The gingival crevice area (supporting structures of the teeth) provides a habitat for a variety of anaerobic species.

Fusobacterium polymorphum is a bacterium that has been isolated from the gingival crevice in humans, and has been implicated in the immunopathology of periodontal disease.

When the gingiva are swollen, the epithelial lining of the gingival crevice becomes ulcerated and the gums will bleed more easily with even gentle brushing, and especially when flossing.