IL-8 secretion from HOK-18A following sequential challenge of F. nucleatum and P. gingivalis. (○) Control group without bacteria. Supernatants were collected at 18 h for IL-8 ELISA. (■) F. nucleatum (MOI, 300:1) was added to cell monolayers and supernatants were collected for IL-8 measurement at the 4-, 8-, or 18-h time point. ↓, P. gingivalis 381 (MOI, 500:1) was added to cell monolayers 4 h (▵) or 8 h (⧫) after the addition of F. nucleatum (MOI, 300:1), and the supernatant was collected at 18 h.