- Porphyromonas gingivalis (P. gingivalis), Escherichia coli (E. coli), Lipopolysaccharide (LPS), Toll-like receptors (TLR), Cytokines, Inflammation.
Monocytes are important cells in innate immunity. The early stage of the innate immunity is regulated by various cytokines produced by monocytes. We conducted a preliminary study to investigate TNFα expression by stimulating THP-1 cells with several bacterial species. The TNFα mRNA levels significantly varied, with the most potent stimulatory effects observed with P. gingivalis. In the present study, we focused on P. gingivalis and compared differences in cytokine expression profiles after the stimulation of THP-1 with E. coli. Bacterial antigen stimulation increased various cytokine gene expressions in THP-1. P. gingivalis had significantly more potent effects on the mRNA expressions of TNFα, IL-1β, and IL-10, but not of IL-12p40, than E. coli. This result suggests the potent ability of P. gingivalis to induce inflammation. THP-1 stimulated with LPS derived from both bacterial species showed that E. coli had significantly more potent effects on the expressions of TNFα, IL-1β, and IL-12p40 than P. gingivalis. The differences in the bacterial antigens and the LPS stimulation effects suggest involvements of different receptors, such as TLR-2 and -4, which recognize bacterial components. The present results suggest that the P. gingivalis somatic cell antigen stimulates a number of pattern recognition receptors at the same time as the synthesis of bacterial components, except LPS. The potent virulence of P. gingivalis and persistence of infection might be affected by differences in cytokine production. Pro-inflammatory responses are dependent not only on the bacterial type, but also bacterial components.