PTGS2 and periodontitis: To identify potential interactions between oral bacteria and inflammatory cytokines in the regulation of the COX-2-PGE2 axis, we infected GFs with two well-characterized oral pathogens, P. gingivalis (ATCC 33277) and F. alocis (ATCC 35896), or the pathobiont F. nucleatum (ATCC 10953) in the absence or presence of TNF—the cytokine detected in large quantities in the gingival tissue of periodontitis patients (23).