This video explains the importance of Apo B in atherogenic particles, such as LDL and Lp(a).

Atherosclerosis results from the deposition of cholesterol into artery walls by lipoproteins, including VLDL, LDL and Lp(a). Lipoproteins consist of cholesterol, triglycerides, phospholipids and apolipoproteins. Apolipoproteins provide lipoproteins with stability, facilitating transport and other functions. Lipoproteins vary in density. LDL is cholesterol-rich, carrying 70% of the body’s cholesterol.
ApoB is the most important apolipoprotein and thus the structural backbone for potentially atherogenic particles including LDL.
ApoB is synthesized in the liver, where it combines with the other constituent parts to form VLDL, a triglyceride-rich particle and a precursor of LDL. An excess of ApoB-containing particles may cause hypercholesterolemia, leading to atherosclerosis.  Measures of ApoB are recognized as leading predictors of cardiovascular risk, reflecting the importance of ApoB in atherogenic particles, such as VLDL, LDL and Lp(a).