Medical Definition of Membrane attack complex
Membrane attack complex: An abnormal activation of the complement (protein) portion of the blood that forms a cascade reaction and brings blood proteins together, binds them to the cell wall, and then inserts them through the cell membrane. Abbreviated MAC. MAC allows water, ions, and other small molecules to move freely into and out of a cell, and it quickly results in cell death.
Subscribe to MedicineNet's General Health Newsletter