CD38 engagement is followed by raft translocation. (A) CD38 molecules were stained with the AT-1 antibody followed by a Texas Red–GαMIg. The cells were then moved to 37°C for 40 minutes before stopping the experiment and staining for the GM1 ganglioside and CD81 using FITC-labeled reagents. (B) Tonsillar B cells were treated with the agonistic anti-CD38 antibody followed by a goat anti–mouse IgG used as a cross-linker for 5 minutes. After treatment, cells were lysed with Brij98 and the different membrane fractions separated by ultracentrifugation. Fractions 2 to 4 and 8 to 9 were pooled together and considered DIM and DSM, respectively. Proteins were precipitated, separated, and immunoblotted for CD38. (C) CD38⁺ tonsillar B cells and L-CD31⁺ or control L-mock fibroblasts were mixed at a 10:1 ratio, cocentrifuged, and incubated at 37°C for the indicated time. After stopping the experiment, CD38 or CD81 molecules were visualized by an indirect method using a Texas Red–GαMIg. Heteroconjugates were identified by visual observation under an Olympus 1 × 71 confocal microscope at 60 × magnification. Images are representative of 6 independent experiments.