Cytotoxic T-Lymphocyte (CTL)-Induced Apoptosis of a Virus-Infected Cell
Killing of the infected cell or tumor cell by apoptosis involves a variety of mechanisms:
Certain granzymes can activate the caspase enzymes that lead to apoptosisof the infected cell. The caspases are proteases that destroy the protein structural scaffolding of the cell - the cytoskeleton - and degrade both the target cell's nucleoprotein and microbial DNA within the cell.
Granzymes cleave a variety of other cellular substrates that contribute to cell death.
The perforin molecules may also polymerize and form pores in the membrane of the infected cell, similar to those produced by MAC. This can increase the permeability of the infected cell and contribute to cell death. If enough perforin pores form, the cell might not be able to exclude ions and water and may undergo cytolysis. A granule called granulysin can also alter the permeability of both miocrobial and host cell membranes.
This animations shows destruction of both the cytoskeleton and nucleoprotein of the infected cell. As the infected cell breaks up into apoptotic fragments, the fragments are subsequently removed by phagocytes. This reduces inflammation and also prevents the release of viruses that have assembled within the infected cell and their spread into uninfected cells.