FIG. 4.

Augmentation of Elk transactivation by the intermediate-affinity TCR ligand is partially dependent on CD4. (A) CD4⁺ or CD4⁻ BW5147 TCR⁺ CD3⁺ CD45RO⁺ cells (clone 18.16) were transfected with the Elk-1–GAL4–5×GAL4–luciferase reporter system and the pRL-CMV internal vector control and stimulated with different concentrations of plate-bound MAb 3D3 or 5A. Luciferase activity was normalized against the internal reporter, and the ratio between the maximal responses obtained with the two MAbs from each cell type was determined. Numbers 1, 2, 3, and 4 indicate separate experiments. (B) Flow cytometric analysis of CD45RO⁺ CD4⁺ (solid) and CD45RO⁺ CD4⁻ (dots) BW cells stained with phycoerythrin-labeled anti-CD4 MAb GK1.5. The cell surface expression of CD45 and the TCR-CD3 complex was also measured and was the same in both cell types (data not shown).