The role of complement in the host's defense against Haemophilus influenzae

J Infect Dis. 1992 Jun;165 Suppl 1:S62-5. doi: 10.1093/infdis/165-supplement_1-s62.


In vitro studies have shown that Haemophilus influenzae type b (Hib) can activate both the classical and alternative pathways of complement and generate complement-dependent opsonic and bactericidal activities. In vivo studies and observations in complement-deficient patients have established the biologic significance of complement in the host's defense against H. influenzae. The complement system plays a significant role in the host's defense against Hib and against other encapsulated and unencapsulated H. influenzae, mainly by enhancing clearance from the bloodstream through its action as an opsonin in both nonimmune and immune hosts. Patients with genetically determined deficiencies of C3 or of the complement components involved in C3 activation have an increased susceptibility to H. influenzae. More recently, a relatively common deficiency of one isotype of C4 (C4B) has been shown to be associated with invasive Hib disease, suggesting that defects in complement-mediated host defense may be more common in systemic Hib infections than previously appreciated.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.
  • Review

MeSH terms

  • Animals
  • Complement Activation
  • Complement Pathway, Alternative
  • Complement Pathway, Classical
  • Complement System Proteins / deficiency
  • Complement System Proteins / immunology*
  • Haemophilus Infections / immunology*
  • Haemophilus influenzae / immunology*
  • Humans
  • Opsonin Proteins


  • Opsonin Proteins
  • Complement System Proteins