Onset of apoptosis in GC (A) and FL cells (B) cultured in media alone or in the presence of cytokines: prolongation of survival in the presence of soluble CD40L. FACS-sorted GC B cells (A) or purified FL cells of a representative patient (B) were cultured in media alone or in the presence of several cytokines (see Materials and Methods) or soluble CD40L for the indicated time and apoptosis was assessed quantitatively by Trypan Blue exclusion at the indicated time points. Similar results were obtained with GC cells isolated from two other tonsils and with FL cells from six additional patients.