Antigenic crossreactivity of the alpha subunit of complement component C8 with the cysteine-rich domain shared by complement component C9 and low density lipoprotein receptor

Proc Natl Acad Sci U S A. 1986 Jun;83(12):4223-7. doi: 10.1073/pnas.83.12.4223.


Complement component C9 contains two distinct cysteine-rich domains exhibiting high sequence resemblance to a domain present in the low density lipoprotein (LDL) receptor and epidermal growth factor precursor, respectively. Antibodies were raised against a peptide corresponding to the most conserved region of the LDL receptor/C9-homology segment. The antibodies were shown by immunoblotting to bind specifically to C9 but also to crossreact with C8 alpha, the alpha subunit of complement component C8. Moreover, a monoclonal antibody to a neoantigen present in polymerized C9 bound to an epitope exposed on C8 within the C5b-8 complex but buried in monomeric C8, suggesting that C8 and C9 undergo similar conformational changes during membrane-attack-complex assembly. Isolated C8 alpha-gamma exhibited the propensity to polymerize in the presence of Zn2+ and urea, as already demonstrated for C9. These data indicate that C8 alpha is closely related, both structurally and functionally, to C9.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Complement C8 / immunology*
  • Complement C9 / immunology*
  • Complement Membrane Attack Complex
  • Complement System Proteins / immunology
  • Cross Reactions
  • Cysteine
  • Epitopes
  • Humans
  • Macromolecular Substances
  • Oligopeptides / chemical synthesis
  • Oligopeptides / immunology
  • Receptors, LDL / immunology*


  • Complement C8
  • Complement C9
  • Complement Membrane Attack Complex
  • Epitopes
  • Macromolecular Substances
  • Oligopeptides
  • Receptors, LDL
  • Complement System Proteins
  • Cysteine