Final answer:
CARD or PYRIN proteins recruit other proteins in the immune system and play a role in signal transduction.
Step-by-step explanation:
CARD (Caspase Activation and Recruitment Domain) or PYRIN (Pyrin Domain) are protein domains that are involved in recruiting other proteins in the immune system. They play a crucial role in signal transduction, which is the process by which cells communicate with each other. CARD proteins recruit other proteins called caspases, which are important for initiating cell death pathways.