Fig. 2.

CD9+ GC-B cells survive better than CD9− GC-B cells in the presence of FDC/HK cells. (A and B) CD9+ and CD9− GC-B cells were cultured with CD40L in the presence or absence of HK cells for 24 h, and Annexin V-FITC and PI binding were measured by flow cytometry to assess apoptosis. (C) GC-B cells were cultured with CD40L in the presence or absence of HK cells for 24 h. In some experiments, GC-B cells were separated from HK cells by transwell inserts. At the end of the culture, cells were stained with either anti-CD9 or isotype control antibodies and analyzed by flow cytometry. The percentage of the surviving CD9+ GC-B cells was determined.