Lipoproteins & apolipoproteins: E, by 'eck.

In December 2008, I wrote about Cholesterol And Coronary Heart Disease , where I used a limousine metaphor to describe how cholesterol & fat are transported around the body. Here's a diagram of a chylomicron lipoprotein "limousine". Chylomicrons transport dietary fat (triglycerides) & cholesterol from the gut to the liver & other tissues. As there's much more dietary fat than dietary cholesterol, the contents are mostly fat.

A chylomicron. T=Triglyceride C=Cholesterol. From http://en.wikipedia.org/wiki/Lipoprotein

The lipoprotein "limousines" vary a lot in size.

(a) VLDL (b) chylomicrons (c) LDL (d) HDL. 
From http://healthcorrelator.blogspot.co.uk/2011/11/triglycerides-vldl-and-industrial.html

Apolipoproteins are the "chauffeurs" which determine to where lipoproteins transport stuff.
Apo A is found mainly on HDL, which transports fat & cholesterol from tissues to the liver.
Apo B is found mainly on LDL, which transports cholesterol from the liver to tissues.
Apo C is found on HDL when fasted, but moves to chylomicrons & VLDL when fat is eaten.
Apo D is found mainly on HDL and is is associated with an enzyme involved in lipoprotein metabolism.
Apo E is found mainly on chylomicrons & IDL and transports lipoproteins, fat-soluble vitamins, and cholesterol into the lymph system and into the blood. In the CNS, Apo E transports cholesterol to neurons. Defects in Apo E result in hyperlipidaemia , cardiovascular & neurological diseases, and is the E referred to in the title.

There's also Apo H, which is a β-glycoprotein involved in the binding of cardiolipin. It has nothing to do with the above lipoproteins.