Deficiency of complement components

Primary immunodeficiency

 * Disorders of all individual components of complement,
 * rare disorders,
 * C1, C2, C3 and C4 disorders manifest as SLE-like immunocomplex diseases; combined with purulent infections,
 * C1 inhibitor defects clinically severe → hereditary angioedema: uncontrolled complement activation occurs after various stimuli → local edema; airway swelling can be fatal,
 * disorders in receptors for complement components include LAD I syndrome (affects CR3),
 * in children with recurrent bacterial and fungal infections, a deficiency of mannose-binding protein (lectin) (MBL), which initiates the lectin pathway of complement activation, has been identified; in adults it is not manifested (compensated by other mechanisms).

Secondary immunodeficiency

 * Reduction of complement components during its depletion, in case of synthesis failure,
 * complement consumption in immunocomplex diseases, septic conditions,
 * in severe liver disease,
 * normalization of liver functions → normalization of complement,
 * transient consumption of C4 in attacks of hereditary angioedema.