BANK1, also known as B-cell scaffold protein with ankyrin repeats 1, is a protein primarily expressed in B lymphocytes — a type of white blood cell essential for adaptive immunity. BANK1 plays a key role in regulating B-cell receptor (BCR) signaling, which is critical for B cell activation and differentiation. As a scaffold protein, BANK1 facilitates the assembly of signaling complexes following BCR engagement by interacting with various molecules such as kinases, phosphatases, and adapter proteins, thereby modulating downstream signaling pathways.