Receptor for transcobalamin saturated with cobalamin (TCbl). Plays an important role in cobalamin uptake. Plasma membrane protein that is expressed on follicular dendritic cells (FDC) and mediates interaction with germinal center B cells. Functions as costimulator to promote B cell responses to antigenic stimuli; promotes B cell differentiation and proliferation. 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). CD320 augments the proliferation of PC precursors generated by IL-10. Interacts (via LDL-receptor class A domains) with TCN2.