CARD games in apoptosis and immunity

A bewildering array of proteins containing the caspase recruitment domain (CARD) have now been identified. Previously, CARD-CARD interactions have been shown to be involved in the assembly of protein complexes that promote caspase processing and activation in the context of apoptosis. However, as the family of CARD-containing proteins has grown, it has become apparent that the majority of these proteins do not recruit caspases or promote caspase activation. Instead, many participate in NF-kappaB signalling pathways associated with innate or adaptive immune responses. Here, we suggest a simplified classification of the CARD proteins based upon their domain structures and discuss the divergent roles of these proteins in the context of host defence.