CD320 is a transmembrane receptor that plays a critical role in vitamin B12 (cobalamin) metabolism by facilitating cellular uptake of transcobalamin-bound cobalamin 1. The receptor is expressed on the luminal surface of intestinal epithelial cells and renal proximal tubules, suggesting roles in both vitamin B12 absorption and reabsorption 2. CD320 functions through receptor-mediated endocytosis, with its cell surface expression dependent on O-glycosylation but not N-glycosylation 3. Beyond vitamin B12 transport, CD320 serves as a costimulatory molecule on follicular dendritic cells, promoting B cell proliferation and differentiation in germinal centers 45. The receptor has emerged as a potential therapeutic target, being overexpressed in many cancers 6. Clinically, CD320 variants can cause transient methylmalonic aciduria in newborns, though most affected individuals show normal cobalamin metabolism beyond infancy 7. Importantly, autoantibodies against CD320 have been identified as causing autoimmune vitamin B12 central deficiency, leading to neurological symptoms despite normal peripheral B12 levels 8. This condition responds to immunosuppression and high-dose B12 supplementation, defining a potential 'anti-CD320-associated syndrome' 9.