Porphyromonas gingivalis lipopolysaccharide promotes T-hel per17 cell differentiation by upregulating Delta-like ligand 4 expression on CD14⁺ monocytes

To investigate the effect and mechanism of Porphyromonas gingivalis (P. gingivalis) lipopolysaccharide (LPS) on Th17 cell differentiation mediated by CD14⁺ monocytes.

P. gingivalis LPS-activated CD14⁺ monocytes were co-cultured with CD4⁺T cells in different cell ratios. An indirect co-culture system was also established using transwell chambers. Furthermore, anti- Delta-like ligand 4 (Dll-4) antibody was used to investigate the role of Dll-4 in Th17 cell response. The mRNA expression was analyzed using quantitative reverse transcription-polymerase chain reaction, and secreted cytokines in culture supernatant were detected using enzyme-linked immunosorbent assay. Flow cytometry was used to determine the frequencies of Th17 cells. IL-17 protein expression levels were determined using western blotting assay.

P. gingivalis LPS increased the expressions of interleukin (IL)-1β, IL-6, IL-23 and transforming growth factor (TGF)-β in CD14⁺ monocytes. Th17 cell frequency upregulated, which is not solely cytokine-dependent but rather requires cell-cell contact with activated monocytes, particularly in the 1:10 cell ratio. Furthermore, P. gingivalis LPS increased t he expression of Dll-4 on CD14⁺ monocytes, whereas the anti- Dll-4 a ntibody decreased the response of Th17 cells. The results suggest that P. gingivalis LPS enhances Th17 cell response via Dll-4 upregulation on CD14⁺ monocytes.