Protects against apoptosis mediated by BAX.Apoptosis, or programmed cell death, is related to many diseases, such as cancer. Apoptosis is triggered by a variety of stimuli including members in the TNF family and prevented by the inhibitor of apoptosis (IAP) proteins. IAP proteins form a conserved gene family including IAP, XIAP/ILP-1/MIHA, and Livin/KIAP that bind to and inhibits specific proteases. A novel member in the IAP protein family was recently identified and designated ILP-2 for IAP-like protein-2 (1). ILP-2 has high homology to ILP-1, but is encoded by a distinct gene that is solely expressed in testis of tested normal human tissues (1). ILP-2, unlike ILP-1, has no inhibitory effect on Fas and TNF induced apoptosis, but potently inhibits apoptosis induced by overexpression of Bax or by coexpression of caspase-9 with Apaf-1. ILP-2 interacts with the processed caspase-9. These results suggest that ILP-2 is a novel IAP family member with restricted specificity for caspase-9.