Morphology of polymorphonuclear neutrophils during periodontal disease in the cynomolgus monkey

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Abstract
The polymorphonuclear neutrophil (PMN) appears to be an important cell in the protection of the host from pathogenic periodontal micro-organisms. The purpose of the present histological studies was to observe the emigration of the PMN from the gingival vessels to the periodontal pocket during gingivitis and ligature-induced periodontitis in the cynomolgus monkey. Two adult female monkeys were treated by application of a silk ligature around selected posterior teeth. After 9 wk, the monkeys were perfused and block sections of both ligated (early periodontitis) and non-ligated (gingivitis) sites were obtained, cut into smaller blocks containing a single interdental area (N = 15 for periodontitis, N = 5 for gingivitis) and processed for light microscopic and EM observations. Morphologically, no differences in PMN between gingivitis and periodontitis were observed and therefore the following description applies to both disease states. In the vessels, the endothelial cells appeared to be actively involved in PMN emigration, maintaining long processes which surrounded the PMN. Within the connective tissue, the PMN maintained their typical morphology which included polylobated nuclei and numerous lysosomal granules. Many intact PMN were observed intercellularly within the connective tissue and the epithelium. Within the periodontal pocket, a multilayer of PMN surrounded the plaque mass. Cells with numerous bacteria-containing phagolysosomes were observed wtih increasing frequency as they approached the plaque. Deeper within the bacterial deposit, PMN were seen in varying stages of degeneration. These histologic studies, when interpreted in the light of reports of severe, rapidly-progressive periodontitis in patients with PMN disorders, suggest that the interaction of PMN with bacterial plaque may serve to maintain a defensive boundary which protects the host tissues from irreversible destruction.