Atherosclerosis is a clogging, narrowing, and hardening of the body's large and medium-sized blood vessels. Atherosclerosis can lead to stroke, and myocardial infarction.
Atherosclerosis is actually a chronic inflammatory response within the walls of arteries. Small lipoproteins like LDL* are able to diffuse through the endothelial wall of blood vessels and accumulate. The inflammatory component of atherosclerosis results from the migration of leukocytes (mainly macrophages) that enter the blood vessel walls. These macrophages seek to remove the deposited LDL as well as intermediate-density lipoproteins (IDL). As macrophages phagocytose these lipoproteins, they become foam cells that get trapped in the endothelial space. This eventually leads to "hardening" or "furring" of the arteries and plaque formation.
*Small dense LDL molecules are known to be more atherogenic than larger, less dense LDL particles. They can more easily move through the basement membrane of the endothelium and into the arterial wall. They may also adhere to glucoproteins more readily and more easily bind to monocytes and macrophages in plaque formation. Thus, small dense LDL molecules would enhance the incorporation of lipid into the plaque.