TNF and rheumatoid arthritis: To examine the effect of IL-1β or TNF-α on the migratory abilities of cells isolated from plica and pannus-like tissue, the cells were seeded into the upper chamber of a porous membrane cell culture insert and allowed to migrate for 24 h across the membrane in the presence or absence of IL-1β or TNF-α or in the presence of IL-1β and IL-1 receptor antagonist (IL-1 RA) or TNF-α and the TNF-α inhibitor Enbrel.