Distribution of P-gp and CD19 in the lipid raft fractions of the plasma membrane. The 12 fractions isolated by sucrose gradient ultracentrifugation of the 1% Triton X-100 cell lysates from Namalwa/MDR1 cells before and after treatment with HD37 or RFB4 were analyzed for the presence of (A) P-gp and (B) CD19. The combined lipid raft fractions from the gradient (3-6) and soluble fractions from the gradient (9-12) were analyzed for the presence of GM1 and CD45, respectively (C). The proteins were electrophoresed on a 6% (P-gp), 7.5% (CD45), 8% (CD19), and 12% SDS-PAGE (GM1), and analyzed by Western blotting using either specific antibodies or HRP-ChB, as indicated in “Materials and methods.”