Inhibition of Monocyte Chemotaxis and Chemokine Macrophage Inflammatory Protein-1 Alpha, and Interleukin-8 Secretion by Lipopolysaccharide Isolated from Periodontal Pathogens

The vast majority of periodontal pathogens are classified as gram negative bacteria. These bacteria have an outermost membrane consisting of lipopolysaccharide (LPS), a molecule that can act as an endotoxin and elicit an immune response. The lipopolysaccharide structure consists of three major regions: oligosaccharide, core, and lipid A. Oligosaccharide is exposed on the cell surface, and lipid A anchors LPS in the outer membrane. LPS has been known to hinder certain defensive mechanisms of the immune system by secreting products that interfere with signals that promote chemotaxis of leukocytes enabling the pathogens to go unrestricted. When LPS binds to the Toll‑like receptor it promotes the secretion of proinflammatory cytokines in cells such as the macrophage, monocyte, and endothelial cells. Two such cytokines stimulated by LPS are macrophage inflammatory protein 1‑alpha (MIP‑1α) and interleukin 8 (IL‑8) both of which have been characterized as potent monocyte chemoattractants. IL‑8 has potency as a chemotactic agent equal to that of C5a. It is a pro-inflammatory mediator of gingivitis and a mediator of the inflammatory response, by serving as a chemical signal that attracts neutrophils. MIP‑1α belongs to a large super family of small inducible cytokines. It is able to stimulate the activity of white blood cells in response to infection or inflammation and is a major factor produced by macrophages stimulated with bacterial endotoxins. The present study examined the interaction of LPS prepared from periodontal pathogens with monocytes, to stimulate them to secrete MIP‑1α and IL‑8. The hypothesis of this study is that LPS molecules of more pathogenic periodontal pathogens suppress the secretion of both MIP‑1α and IL‑8, in such a way that they can escape detection by the defensive cells, thus facilitating their ability to colonize the oral cavity and may contribute to their pathogenicity. The LPS from three different periodontal pathogens, Porphyromonas gingivalis, Prevotella denticola, and Fusobacterium nucleatum were isolated under identical conditions. Cultured human monocytic cells were incubated with different concentrations of LPS and then the secretion of MIP‑1α and IL‑8 was measured by enzyme‑linked immunosorbent assay (ELISA). The results demonstrated that LPS of different periodontal pathogens differ in their ability to stimulate inflammatory cytokines. LPS of P. gingivalisand P. denticola were found to suppress the secretion of both IL‑8 and MIP‑1α at higher concentrations. On the other hand, LPS of F. nucleatumstimulated the secretion of IL‑8 and MIP‑1α, by monocytes in a dose dependent manner. The long term objective is to understand the mechanisms by which the periodontal pathogens escape detection by interfering with host defensive functions, such as chemotaxis. This study presents a possible mechanism of chemotaxis interference by LPS from periodontal pathogens by inhibiting the secretion of both MIP‑1α and IL‑8. With an understanding of the mechanism by which LPS molecules interfere with chemotaxis, it may be possible to intervene and prevent the tissue destruction associated with periodontal pathogens