HSPA8 is the ligand of EWI-2. (a to f) Jurkat cells were treated either with a combination of two HSPA8-specific siRNAs (gray shaded profiles) or with control siRNA (QIAGEN AllStars) (black empty histograms). Binding of sEWI-2-hIg (a and d) and of a control protein (b and e) and the expression of CD81 (c and f) were analyzed 20 h (left column [panels a, b, and c]) or 60 h (right column [panels d, e, and f]) after treatment. (g) Binding of 10 pM sEWI-2-hIg in fluid phase to the following BIACORE chip-immobilized proteins: human HSPA8, anti-EWI-2 mAb 5E8, and human hsp60. (h) The same experiment was performed in the presence of 10 μM ATP. One representative experiment out of three (each using independent protein preparations) is shown.