Complement deficiencies

The complement system, an integral part of the innate immune system, consists of a series of plasma proteins that collaborate to eradicate pathogens, promote inflammation, and fine-tune the adaptive immune response. Complement proteins are involved in chemotaxis, cell lysis and opsonisation. Deficiencies in the complement system can increase susceptibility to infections, autoimmune disorders, or other conditions.

C1 inhibitor (C1-INH) protein deficiency

causes hereditary angioedema
C1-INH is a multifunctional serine protease inhibitor
probable mechanism is uncontrolled release of bradykinin resulting in oedema of tissues

C1q, C1rs, C2, C4 deficiency (classical pathway components)

predisposes to immune complex disease
e.g. SLE, Henoch-Schonlein Purpura
also predisposes to bacterial infections, but less severe than C3 deficiency

C3 deficiency

presents early in life; can be fatal without treatment
causes severe, recurrent bacterial infections with encapsulated organisms

C5 deficiency

predisposes to Leiner disease
recurrent diarrhoea, wasting and seborrhoeic dermatitis

C5-9 deficiency

encodes the membrane attack complex (MAC)
particularly prone to Neisseria meningitidis infection

+PassMedicine Notes

C1 inhibitor (C1-INH) protein deficiency

causes hereditary angioedema
C1-INH is a multifunctional serine protease inhibitor
probable mechanism is uncontrolled release of bradykinin resulting in oedema of tissues

C1q, C1rs, C2, C4 deficiency (classical pathway components)