Translocation of Porphyromonas gingivalis infected monocytes and associated cellular responses

Porphyromonas gingivalis (P. gingivalis), an important periodontal pathogen in adult chronic periodontitis, has been reported to colocalize in human atheromatous lesions. We have studied the phagocytosis and survival of P. gingivalis in human monocytes, together with the cellular responses of infected human monocytes. Human monocytes were cocultured with P. gingivalis and the external bacteria were killed with metronidazole and gentamycin. Localization of P. gingivalis in cells was studied by transmission electron microscopy (TEM). The survival of P. gingivalis was determined by lysing the monocytes and plating on blood agar under anaerobic conditions. Interleukin-1 beta (IL-1beta) and tumor necrosis factor-alpha (TNF-alpha) were determined using specific enzyme-linked immunosorbent assays (ELISAs) kits. The transwell chamber system was used to investigate the chemotactic response of the infected cells. TEM showed that P. gingivalis organisms were localized within the autophagosome-like structure of monocytes. No significant difference on the survival of P. gingivalis at 0, 4 and 8 h after infection was found. IL-1beta and TNF-alpha were present in the cell culture media in response to bacterial challenge. The infected monocytes showed a normal chemotactic response to monocyte chemotactic protein-1 (MCP-1). The number of monocyte cells migrating through membrane in the presence and absence of P. gingivalis were 18.64 +/- 2.33 x 10(4) cells and 19.11 +/- 1.76 x 10(4) cells respectively. The number of viable P. gingivalis per monocyte following translocation in response to the chemotactic gradient was 5.83 +/- 1.45 x 10(-3) CFU/cell. The results indicate that P. gingivalis can stimulate cytokine production and survive in monocytes without affecting cell migration.