ARPC1B (Actin Related Protein 2/3 Complex Subunit 1B) is a gene that encodes a component of the ARP2/3 complex, a key regulator of actin cytoskeleton organization and cell movement. It is essential for proper immune cell function and the body’s defense against infections. Mutations in ARPC1B can cause a rare immunodeficiency disorder, known as ARPC1B deficiency, which impairs immune response.