Caspase-8 association with FADD, RIP1, and FLIP proteins in cells undergoing macrophagic differentiation. (A) Peripheral-blood monocytes (Mo) were treated for 2 days as in Figure 1 to induce their differentiation into macrophages (Mac) or dendritic cells (DC) before lysis. These lysates were used for immunoblotting before (Lysates) or after (IP:casp-8) immunoprecipitation with an anti–caspase-8 antibody. (B) U937 cells were exposed to 20 nM TPA for indicated times (hours) before analysis as in panel A or using an anti-FLIP antibody (IP:FLIP) for immunoprecipitation. Molecular weights are in kilodaltons. The asterisk indicates cleavage products. Beads are a negative control without antibody for immunoprecipitation. One representative of at least 3 independent experiments is shown.