AP3B1 encodes the β1 subunit of the adaptor protein complex 3 (AP-3), a critical component of vesicular trafficking machinery. AP-3 functions in protein sorting within the trans-Golgi network and endosomes, mediating recognition of cargo sorting signals and recruitment of clathrin to membranes 1. AP-3B1 is essential for lysosomal biogenesis and targeting cargo to lysosomes and lysosome-related organelles, including melanosomes and platelet dense granules 1. In concert with BLOC-1, AP-3 directs neuronal cargo into vesicles for anterograde axonal transport to nerve terminals 1. Dysfunction of AP3B1 causes Hermansky-Pudlak syndrome type 2 (HPS2), an autosomal recessive disorder characterized by oculocutaneous albinism, platelet storage pool deficiency with hemorrhagic diathesis, and severe neutropenia with recurrent infections 2. AP3B1 mutations are also associated with hemophagocytic lymphohistiocytosis (HLH) due to impaired cytotoxic granule biogenesis in CD8+ T cells and NK cells 3. Beyond genetic disease, AP3B1 demonstrates antiviral functions: it restricts rabies virus through PDIA3-mediated selective autophagy of viral glycoproteins 4 and suppresses SARS-CoV-2 replication through interactions with the viral envelope protein 5. These findings suggest AP3B1 represents a potential therapeutic target across multiple disease contexts.