SPPL3 (Signal Peptide Peptidase-Like 3) is an enzyme in the intramembrane-cleaving protease family that processes certain transmembrane proteins. By releasing intracellular domains from its substrates, SPPL3 influences cellular signaling and regulation. It plays a key role in immune system function, including B cell maturation, and has been linked to some autoimmune conditions. Studying SPPL3 helps reveal how intramembrane proteolysis impacts human health and disease.