Phagocytosis
In phagocytosis, phagocytes are attracted to the area of invasion by chemical products of the
microorganism, phospholipids released by injured mammalian cells, or by components of the
complement system. The phagocyte moves into the area of invasion and then attaches to the
microorganism. The attachment is mediated by a variety of surface receptors including antibody,
lipopolysaccharide, and complement receptors.
For example, the C3b component of complement coats bacteria or other particles and then binds
to C3b receptors on the phagocyte. This process of coating to enhance phagocytosis is called
opsonization. The microorganism is then engulfed by the phagocyte into a vacuole known as a
phagosome.
Vesicles in the cytoplasm called lysosomes fuse with the phagosome, releasing digestive
enzymes such as lysozyme and proteases into the phagosome. The structure resulting from this
fusion is called a phagolysosome. Inside the phagolysosome, microorganisms are killed and
digested.
Finally, the digested contents of the phagolysosome are eliminated from the phagocyte by
exocytosis.