Changes in bcl-x_L expression in FL cells (A) and GC (B) upon culture in media alone or in the presence of sCD40L; bcl-2 levels are not affected. Highly purified FL cells (A) and FACS-sorted CD38⁺ GC B cells (B) were cultured in media alone or in the presence of soluble CD40L. At the indicated time intervals, cells were isolated, cell lysates were prepared, and 3 × 10⁶ cells were analyzed by SDS-PAGE and Western blotting using anti–mcl-1 polyclonal antiserum (first panel), anti–bcl-x polyclonal antiserum (second panel), and anti–bcl-2 MoAb (third panel). Expression of the different proteins was quantitated in each lane using a Scanner phosphoimager (Alpha Innotech Corp).