Chronic treatment with TNF-α in combination with either IL-4 (A) or IL-13 (B) can maintain elevated VCAM-1 expression on fibroblast-like synoviocytes for up to 16 days. Cells were treated with either medium only (open circles), TNF-α (10 ng/ml) (closed circles), IL-4 (10 ng/ml) (open squares) , or IL-4 plus TNF-α (both at 10 ng/ml) (closed squares), IL-13 (10 ng/ml) (open triangles), or IL-13 plus TNF-α (both at 10 ng/ml) (closed triangles) at day 0. Cytokines were re-added at days 4, 8, 12, and 16 over a 20-day period. Cell surface VCAM-1 expression was measured 4 days after cytokine application in a flow cytometry protocol with the aid of mAb BBA-5. Results are expressed as corrected MFI. Data are presented as the mean ± SE of four experiments. *, P < 0.05; **, P < 0.01; ***, P < 0.001. (In the top panel comparison is between IL-4 alone and IL-4 plus TNF-α and in the bottom panel IL-13 alone is compared with IL-13 plus TNF-α). In addition, for both IL-4 and IL-13 alone, VCAM-1 expression was significantly different from medium-only control (P < 0.05) at days 4 and 8.