Antibodies against members of the Bcl-2 family are valuable tools in studying apoptosis and related processes. This family consists of 25 members, some of which play opposing regulatory roles. Most members including Bcl-2, Bcl-Xl, and Bcl-W function to inhibit apoptosis by preventing the release of mitochondrial components such as cytochrome c, leading to caspase activation. This counteracts the function of family members Bax and Bak which promote mitochondrial release and cell death. Other pro-apoptotic members such as Bid, Bad, Bik, Bim and Puma, despite their lack of protein similarity to Bcl-2, are included in the family based on their affinity to bind and inhibit antiapoptotic Bcl-2 proteins.