Fig. 6. Inhibition effect of a splice variant on 4-1BB signaling. (A) EL4 cells were transiently transfected with the indicated expression plasmids of pCDNA3.1-4-1BB, pCDNA3.1-4-1BBL, or pCDNA3.1-ΔE8-4-1BB. pELAM-luc reporter plasmid and pCMV-β-gal were co-transfected. Luciferase activities were measured 24 h after transfection and normalized on the basis of β-galactosidase activity. Values are presented as means±s.e. Each experiment was performed in triplicate, and the data presented are representative of three different experiments. (B) The surface expression of 4-1BB on EL4 cells transfected with pCDNA3.1, pCDNA3.1-4-1BB, or pCDNA3.1-ΔE8-4-1BB was determined by staining with FITC conjugated 3E1 mAb and an isotype control. (C) RT-PCR performed with identical samples. (D) Soluble 4-1BB protein was measured by ELISA using the supernatant from transfected EL4 cells. A Wallac vector 1420 Multilabel Counter was used for measurement. Data are representative of three independent experiments. Values are presented as means ± s.e.