Complement Biology
In the presence of foreign particles, complement proteins become activated and bind
to the surface of these particles. This triggers a cascade, or chain reaction, among
complement proteins, with one protein leading directly to the creation of the next
one in the complement cascade. Complement proteins then form holes or pores in the
invading organisms, causing their destruction. Complement proteins can also mark
foreign particles so that white blood cells can remove them. Complement proteins,
once activated, can trigger other reactions on host cells and on cells of the immune
system, further increasing the destruction of foreign particles. Complement proteins
also clean up left over antibody complexes for disposal in the spleen and liver.
Complement plays a role in many diseases. In PNH for example, a genetic error in
cell proteins results in a deficiency in complement inhibitors that normally protect
red blood cells, making the PNH red blood cells vulnerable to complement destruction.1
PNH red blood cells are then recognized by the immune system as foreign particles,
and are destroyed by complement. The contents of the red blood cell are emptied
into the blood stream and cause many of the symptoms that patients suffer such as
thrombosis, anemia, abdominal pain and erectile dysfunction.2 Patients
endure blood clots, recurrent pain, disabling fatigue3, shortness of
breath, pulmonary hypertension4, impaired kidney function, anemia, transfusions,
a poor quality of life and a heightened risk of mortality3,5