Porphyromonas gingivalis cell wall components induce PD-L1 expression on human oral carcinoma cells by a RIP2-dependent mechanism

Programmed death-ligand 1 (PD-L1/B7-H1) serves as a co-signalling molecule in cell-mediated immune responses and contributes to chronicity of inflammation and the escape of tumor cells from immunosurveillance. Here we investigated the molecular mechanisms leading to PD-L1 upregulation of human oral carcinoma cells and in primary human gingival keratinocytes in response to infection with Porphyromonas gingivalis (P. gingivalis), a keystone pathogen for the development of periodontitis. The bacterial cell wall component peptidoglycan uses bacterial outer membrane vesicles to be taken up by the cells. Internalized peptidoglycan triggers cytosolic receptors to induce PD-L1 expression in a myeloid differentiation primary response 88 (Myd88)-independent and receptor-interacting serine/threonine-protein kinase 2 (RIP2)-dependent fashion. Interference with the kinase activity RIP2 or mitogen-activated protein (MAP) kinases interferes with inducible PD-L1 expression.