Macrophages/white blood cells who wish to save you from those stuck particles.

The real question is what causes the blood vessel walls to get damaged (since the scar tissue is the healing response of the body, but if the damage keeps on piling it grows too much instead of being gradually reduced over time).

The problem is that there are millions of causes of inflamation etc...

In general the best answer is "modern diet" full of sugars + fat at the same time.

Carbs in high doses are poisonus, there is a reason the the lives of diabetics end in limb amputation, blindness and severe pain due to nerve damage due to sugar destroying them from the inside out...