Fig. 5. TNF- disrupts contact-mediated inhibition of cell proliferation. 2A4 cells were seeded at saturation density within a glass cylinder placed in the centre of a 22 mm well. After 24 hours, the cylinder was removed and the monolayer was incubated with or without TNF-. (A) When left untreated for 9 days, the initial cobblestone-like monolayer of 2A4 cells remain strictly contact inhibited. (B) Over the same time period, 2A4 cells treated with 5 ng ml^-1 TNF- have formed thick ridges overlying the initial monolayer. (C) Thin section perpendicular to the plane of a control culture showing that the cells grow as a single layer. (D) Thin section perpendicular to the plane of a culture treated with 3 ng ml^-1 TNF-. The cells pile up forming multiple cell layers. Scale bars, 200 µm (A,B); 10 µm (C,D).