 It is a 29 kDa glycoprotein discovered in 1963 as a component of the High Density Lipoprotein (HDL) fraction of human plasma.It is the major component of human mammary cyst fluid.The human gene encoding it was cloned in 1986 and the deduced protein sequence revealed that ApoD is a member of the lipocalin family, small hydrophobic molecule transporters (Drayna et al, 1986).