DEFICIENCIES
OF THE COMPLEMENT SYSTEM
The complement system is an integral part of the immune system, and alterations in normal components of complement can result in increased susceptibility to infectious diseases and to immune-mediated disorders (Porth, 2002). Improved techniques to iden-tify the individual components of the complement system have led to a steady increase in the number of deficiencies identified. Dis-orders of the complement system can be primary or secondary.
C2 and
C3 component deficiencies result in diminished resis-tance to bacterial
infections. Angioneurotic edema is
caused by an inherited deficiency of the inhibitor of C1 esterase, which
op-poses the release of inflammatory mediators. A deficiency of this inhibitor
results in frequent episodes of urticaria and edema in various parts of the
body.
Patients
with paroxysmal nocturnal hemoglobinuria (PNH) lack decay-accelerating factor
(DAF), which is found on erythro-cytes (red blood cells). DAF normally protects
the erythrocytes from lysis (disintegration). In PNH, the complement component
C3b accumulates on the CR1 molecule on the erythrocyte, acts as a binding site
for the late-acting component, and allows lysis to occur.
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