The function of CD320 (CD320 molecule, Ensembl gene identifier ENSG00000167775) is as follows. Receptor for transcobalamin saturated with cobalamin (TCbl) (PubMed:18779389). Plays an important role in cobalamin uptake (PubMed:18779389, PubMed:20524213). Plasma membrane protein that is expressed on follicular dendritic cells (FDC) and mediates interaction with germinal center B cells (PubMed:10727470). Functions as costimulator to promote B cell responses to antigenic stimuli; promotes B cell differentiation and proliferation (PubMed:10727470, PubMed:11418631). Germinal center-B (GC-B) cells differentiate into memory B-cells and plasma cells (PC) through interaction with T-cells and follicular dendritic cells (FDC) (PubMed:11418631). CD320 augments the proliferation of PC precursors generated by IL-10 (PubMed:11418631). {ECO:0000269|PubMed:10727470, ECO:0000269|PubMed:11418631, ECO:0000269|PubMed:18779389, ECO:0000269|PubMed:20524213}.