Infections due to complement deficiencies – a general introduction
One important function of complement is to protect the host from microbial infections. Thus, complement deficiencies predispose to an increased susceptibility to infection, in particular caused by Neisseria meningitidis (Table 1), but also represent an increased risk for other, mainly autoimmune diseases (ref 1). Genetically determined deficiencies are described for almost all complement proteins. Of note, complete deficiencies may have a different outcome than subtotal deficiencies (ref 2) and specific allotypes may also predispose to infections.
Table 1. Genetically determined complement deficiencies and associated infections (adapted from ref 1):
|Protein||Infection susceptibility including typically involved microorganisms|
|C1q||Sepsis, meningitis, pneumonia / Str. pneumoniae, N. meningitidis (Nm)|
|C1rs, C4||Sepsis, meningitis, pneumonia / encapsulated bacteria|
|C2||Sepsis, meningitis, pneumonia, osteitis / Str. pneumoniae, Sta. aureus, Nm|
|C3||Respiratory tract infections / Nm, Str. pneumoniae, H. influenza, Str. pyogenes|
|Factor D||Meningitis / Nm|
|Properdin||Meningitis / Nm|
|Factors H, I||Recurrent pyogenic infections / N. meningitidis, H. influenza, Str. pneumoniae|
|MBL; MASP2||Respiratory tract infections|
|C5-C9||Recurrent meningitis & sepsis / N. meningitidis|
2. Würzner R, Hobart MJ, Fernie BA, Mewar D, Potter PC, Orren A, Lachmann PJ. Molecular basis of subtotal complement C6 deficiency. A carboxy-terminally truncated but functionally active C6. J Clin Invest 1995;95:1877–1883.