Detection of MRP3 in a GBM cell line and in MRP3-transfected cells. (A) Western Blot. Lane 1, reactivity of purified IgG from rabbit anti-MAR3 antiserum 1780 for fusion protein MAR3-MBP (~69 kD); lanes 2 and 3, protein extract (10 μg) of HEK293 cells transfected with the parental pcDNA3.1 and with pcDNA3.1-MRP3 plasmid, respectively; lane 4, protein extracts (10 μg) of MRP3-positive T98G cells that were electrophoresed and probed with rabbit anti-MAR3 antiserum 1708. The ~185-kDa mature MRP3 protein is indicated by an arrow. The locations of protein molecular weight markers are shown to the left. (B) Indirect FACS analysis. Reactivity of MAb 16A11 for non-permeabilized MRP3-expressing T98G cells, demonstration of a cell surface epitope. Irrelevant purified murine IgG2a was used as a negative control. (C) Quantitative FACS analysis of purified, directly fluoresceinated MRP3-specific MAb 16A11 with established human glioma cell line D54 MG; median MRP3 antigen density/cell: 4.4 × 104. (D) Quantitative FACS analysis of MAb 16A11 with human glioma biopsy sample TB 2155 MG; median MRP3 antigen density/cell: 2.7 × 104.