Staining results for MVP in a panel of cell lines with known presence or absence of MVP (A) and in frozen sections of normal human lung (B). Preparations were pretreated using the guanidine method (see Materials and methods) and stained with MVP-φ4, control Fab or MVP-37 murine Mab. Biotinylated rabbit-anti-mouse and HRP-labelled streptavidin were used as secondary reagents for the mouse Mab. For detection of the human Fabs, 9E10 Mab and HRP-labelled rabbit-anti-mouse serum was used. Colour development was with AEC/H2O2. Both the anti-MVP Fab MVP-φ4 and the murine Mab MVP-37 show, as expected, the presence of MVP in the GLC4 ADR cells, the SW1573/2R120 cells and in a characteristic low percentage of cells in the MDR1 P-gp positive SW1573/2R160 cells (A). Furthermore, MVP-φ4 and MVP-37 show the presence of MVP in the epithelial cells of the bronchi of the lung (B).