Apolipoprotein D (ApoD), carried on HDL, can facilitate lipid exchange between circulating lipoproteins.

“we actually have a protein it's pretty much carried on hdls it was originally called April protein or April lipoprotein D as in thought capital D and in my dirty New Jersey mind think of an HDL particle which carries most of the a PO d you men carry something between their legs that if it got erect it's sticking up and it can penetrate something else so if HCL's are carrying it's a po d and it suddenly sticks up it can penetrate it another particle b it another HDL or an April B particle and that's a phospholipid sort of tunnel let's say it's like a little tunnel that can connect to circulating lipoproteins and therefore the core lipids can exchange”