# Opsonin --- An **opsonin** is a protein in the [[immune system]] that binds to particles in a way that facilitates [[phagocytosis]], or other immune responces. Opsinization is the act of making those foreign particles more likely to be phagocotized, by coating it with opsonins. ## Types The main two types of opsonins are [[complement protein|complement proteins]] and [[antibodies]]. ## Opsonins and Capsules When a bacteria has the ability to make a [[capsule]], it can be problematic for the immune system because it effectivly hides any opsonin that may have attached to it. If the [[phagocytosis|phagocyte]] cannot see the opsonins, then they are effectivly back to square one. Some capsules can even break down complement proteins that have attached to them. ___