Verification of pIN-KDEL expression and intracellular retention. A. Immunoblots of lysates from transfected HEK293 cells reveal bands corresponding to the anticipated sizes for pIN-G (41.3 kDa) (Lane 1) and the smaller (31.4 kDa) pIN-MDEL (Lane 2) and pIN-KDEL (Lane 3) proteins. Identical sized proteins were obtained through transduction of HEK293 cells with a lentivirus encoding pIN-MDEL (Lane 4) and pIN-KDEL (Lane 5). A band corresponding to EGFP (Lane 6) is shown for comparison. Transfection, transduction and immunoblotting were done as described in Materials and Methods. Immunoblots were analysed using anti-GFP at 1:4000 dilution. B. Anti-EGFP ELISA at 48 h post-transfection reveals the presence of EGFP immunoreactivity in the culture medium from cells expressing pIN-MDEL, but not pIN-KDEL, when compared to HEK293 cultures that were mock-transfected or transfected with insert-free plasmid.