B-CLL cells were cultivated with 100 mg of exosomes in a final volume of 2 ml for two days. Induction of surface accessory molecules was measured by flow cytometry using a FACS Calibur flow cytometer (Becton Dickinson). For bead-coupling assays 5 ml of surfactant-free sulfate/aldehyde latex beads were incubated with 10 mg of exosomes for 15 min at room temperature. Then 1 ml of PBS was added and the beads were incubated for another 2 hours. The beads were washed three times in PBS with 2% FCS and analyzed. Antibodies specific for tsg101 (sc-978) and CD154 (sc-7964) were purchased from Santa Cruz Biotechnology. E. Kremmer (Munich) provided the gp350-specific antibody 72A1. Fluorochrome-labeled secondary antibodies were obtained from Becton Dickinson (Heidelberg, Germany) or Immunotools (Friesoyte, Germany).