Complement Immunodeficiencies

Complement Deficiencies

Complement deficiencies include the following conditions:

◗ Recurrent infections

This is a condition caused by a deficiency of C1, C3, or C5, or even C6, C7, or C8 components of the complement. Patients with C3 deficiency are highly susceptible to infection with S. aureus and other pyogenic bacteria. Similarly, patients withC6, C7, or C8 deficiency are more susceptible to bacteremia with N. meningitidis or Neisseria gonorrhoeae.

◗ Autoimmune diseases

Patients with deficiencies in C2 and C4 components have disease resembling systemic lupus erythematosus or other autoimmune diseases. Patients with C2 deficiency are usually asymptomatic, and C2 deficiency is the most common comple-ment defect.

◗ Paroxysmal nocturnal hemoglobinuria

It is a disease characterized by hemoglobinuria during night when patient is asleep. The hemoglobinuria occurs due to a complement-mediated hemolysis, especially at night. This is because the lower concentration of oxygen in the blood during sleep increases the susceptibility of the red blood cells to lysis. This occurs in the patients with a defect in the gene for the molecules that attach decay-accelerating factor (DAF) and other proteins to the cell membrane. This results in a deficiency of DAF on the surface of blood cell precursors, leading to an increased activation of complement and increased hemolysis.

◗ Hereditary angioedema

Hereditary angioedema is a disease caused by a deficiency of C1 inhibitor, a component of the complement. This deficiency results in the continual action of C1 on C4 to produce more C4a and subsequently more C3a and C5a complement compo-nents. An increased production of the vasoactive components, such as C3a and C5a, results in the production of capillary permeability and edema in larynx and several other organs. Steroids (such as oxymetholone and danazol) are used to treat the condition, because they increase the concentration of C1 inhibitors, thereby preventing increased production of more C3a and C5a.