Constitutive activation of NF-AT in p-ERK1/2–positive CLL cells. Nuclear extracts of purified CLL cells from 6 p-ERK⁺ and 6 p-ERK⁻ CLL patients, of Daudi (p-ERK⁻) and MEC1 cells (p-ERK⁺) were examined for NF-ATc activation by an enzyme-linked immunosorbent assay (ELISA)–based assay as described in “Antibodies and reagents.” A specific competing oligonucleotide was added to determine specificity of binding. Error bars represent SD.