Streptococcus pneumoniae evades complement attack and opsonophagocytosis by expressing the pspC locus-encoded Hic protein that binds to short consensus repeats 8-11 of factor H

J Immunol. 2002 Feb 15;168(4):1886-94. doi: 10.4049/jimmunol.168.4.1886.

Abstract

Streptococcus pneumoniae is an important cause of upper and lower respiratory tract infections, meningitis, peritonitis, bacterial arthritis, and sepsis. Here we have studied a novel immune evasion mechanism of serotype 3 pneumococci, which are particularly resistant to phagocytosis. On their surfaces the bacteria express the factor H-binding inhibitor of complement (Hic), a protein of the pneumococcal surface protein C family. Using radioligand binding, microtiter plate assays, surface plasmon resonance analysis, and recombinant constructs of factor H, we located the binding site of Hic to short consensus repeats (SCRs) 8-11 in the middle part of factor H. This represents a novel microbial interaction region on factor H. The only other ligand known so far for SCRs 8-11 of factor H is C-reactive protein (CRP), an acute phase protein that binds to the pneumococcal C-polysaccharide. The binding sites of Hic and CRP within the SCR8-11 region were different, however, because CRP did not inhibit the binding of Hic and required calcium for binding. Binding of factor H to Hic-expressing pneumococci promoted factor I-mediated cleavage of C3b and restricted phagocytosis of pneumococci. Thus, virulent pneumococci avoid complement attack and opsonophagocytosis by recruiting functionally active factor H with the Hic surface protein. Hic binds to a previously unrecognized microbial interaction site in the middle part of factor H.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Bacterial Proteins*
  • Binding Sites
  • Binding, Competitive
  • C-Reactive Protein / metabolism
  • Carrier Proteins / biosynthesis
  • Carrier Proteins / genetics
  • Carrier Proteins / metabolism*
  • Complement Activation*
  • Complement C3b / metabolism
  • Complement Factor H / chemistry*
  • Complement Factor H / genetics
  • Complement Factor H / metabolism*
  • Consensus Sequence
  • Enzyme-Linked Immunosorbent Assay
  • Humans
  • Kinetics
  • Opsonin Proteins / immunology
  • Phagocytosis
  • Recombinant Proteins / metabolism
  • Repetitive Sequences, Amino Acid
  • Sequence Deletion
  • Streptococcus pneumoniae / metabolism
  • Streptococcus pneumoniae / pathogenicity*
  • Surface Plasmon Resonance

Substances

  • Bacterial Proteins
  • CFH protein, human
  • Carrier Proteins
  • Hic protein, Streptococcus pneumoniae
  • Opsonin Proteins
  • Recombinant Proteins
  • Complement C3b
  • Complement Factor H
  • C-Reactive Protein