Distribution and roles of neutrophilic polymorphonuclear leukocytes in experimental gingivitis in rats.

For the purpose to study on the distribution and role of polymorphonuclear leukocytes (PML) in the junctional epithelium (JE) in gingivitis, morphological changes of the rat molar JE following topical application of sterile saline, squid ink, latex particles, hyaluronidase and lipopolysaccharide were examined by light and electron microscopy. Ultrastructure of the gingival pocket induced by experimental plaque accumulation on the rat molar teeth was also studied. Small numbers of PML were always revealed under phygiologcal condition in the JE and gingival sulcus, while they rapidly increased in number and extent of distribution after topical application of those substances. In the gingival pockets, regardless of their depth or width, and pocket-lining epithelium, numerous PML were also present and formed a dense layer surrounding the bacterial plaque. Desmosome-like structures were often demonstrated on the closely adjoining cytoplasmic membranes between PML around the plaque. PML within gingival sulcus and/or pocket were often found to phagocytose bacteria, squid ink and latex particles. These observations strongly suggested that PML in the JE, gingival sulcus, and even in the gingival pocket as well as the pocket epithelium might form a strong protective barrier against the irritants from the oral cavity.