CD320 antigen is also known as 8D6 antigen，FDC-signaling molecule 8D6，Transcobalamin receptor and 8D6A. It is a single-pass type I membrane protein and containing two LDL-receptor class A domains. CD320 has been recently discovered and reported as a follicular dendritic cell (FDC) protein. CD320 can augments the proliferation of plasma cells precursors generated by IL-10. CD320 also founctions a receptor for the cellular uptake of transcobalamin bound cobalamin. Defects in CD320 are the cause of methylmalonic aciduria type TCblR (MMATC) which is a metabolic disorder.