Internal Medicine-Allergy & Immunology
Defects in complement proteins
- Deficiency of the classical pathway components (C1q, C1r, C1s, C2 and C4). Propensity to immune-complex diseases (like SLE).
- Deficiency of C3, factor H, and factor I. Propensity to pyogenic infections (because of C3 role in opsonization).
- Deficiency of terminal components (C5, C6, C7, C8) and alternative pathway (properdin and factor D). Propensity for infections with Neisseria gonorrheae and N. meningitidis.
- Deficiency of C9 is asymptomatic.
- Deficiency of C1 inhibitor (hereditary angioneurotic edema). This is clinically the most important deficiency of complement. Look in “hot topic” – hereditary angioneurotic edema.
