The HTLV-I receptor localizes in GM1-containing lipid rafts. HOS cells were treated with HTSU-Fc and biotin-labeled cholera toxin and visualized with (A) FITC-labeled anti-rabbit IgG and Cy3-labeled anti-biotin antibody, or (B) biotin-labeled anti-rabbit IgG and Cy3-labeled antibiotin antibody and FITC-labeled anti-transferrin receptor (TfR) antibody. Representative fields are shown using filters allowing visualization of only (A) FITC-labeled HTLV-I receptor (top panels), Cy3 labeled GM1 (middle panels), or both (bottom panels), and (B) Cy3 labeled HTLV receptor (left panels), FITC-labeled TfR (middle panels), or both (right panels).