Phagocytosis is a common method used within cell-mediated immunity to kill foreign cells. On the binding of the phagocyte to the target cell, endocytosis brings the pathogen into the phagocyte, enclosing it in a phagosome.
The phagosome is a special vesicle containing the pathogen, into which lysozymes, from lysosomes are deposited. This is through the fusion of the phagosome with lysosomes in the phagocyte, forming a phagolysosome.
Lysozymes are important in digesting the pathogen and rendering it inert. The products of these reactions can either be internalised into the phagocyte, or released into the extracellular fluid for other cells to take up.
Some pathogens, such as Legionella, can grow in the phagosome. By producing special proteins that insert into the phagosome membrane, the fusion of lysosomes can be prevented. This allows the intracellular growth of the pathogen. Normally, this process occurs with bacteria that are adapted for intracellular growth in amoebae.