Human immunodeficiency virus type 1 activates the classical pathway of complement by direct C1 binding through specific sites in the transmembrane glycoprotein gp41

J Exp Med. 1991 Dec 1;174(6):1417-24. doi: 10.1084/jem.174.6.1417.

Abstract

Human immunodeficiency virus type 1 (HIV-1), in contrast to animal retroviruses such as murine leukemia virus, is not lysed by human complement. Nevertheless, HIV-1 activates complement via the classical pathway independent of antibody, and C3b deposition facilitates infection of complement receptor-bearing cells. Using gel exclusion chromatography on Sephacryl S-1000, purified virions were found to bind 125I-labeled C1q, but not 125I-labeled dimeric proenzyme C1s. Virions activated the C1 complex, reconstituted from C1q, proenzyme C1r, and 125I-labeled proenzyme C1s, to an extent comparable with that obtained with immunoglobulin G-ovalbumin immune complexes. To determine the activating viral component, recombinant viral proteins were used: in the solid phase, soluble gp41 (sgp41) (the outer membrane part of gp41, residues 539-684 of gp160) bound C1q, but not dimeric proenzyme C1s, while gp120 was ineffective. In the fluid phase, sgp41 activated the C1 complex in a dose- and time-dependent manner, more efficiently than aggregated Ig, but less efficiently than immune complexes. To localize the C1 activating site(s) in gp41, synthetic peptides (15-residue oligomers spanning amino acids 531-695 of gp160) were used. Peptides covering positions 591-605 and 601-620 and, to a lesser extent, positions 561-575, had both the ability to bind C1q and to induce C3 deposition. These data provide the first experimental evidence of a direct interaction between the C1 complex and HIV-1, and indicate that C1 binding and activation are mediated by specific sites in gp41.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Binding Sites
  • Complement C1 / metabolism*
  • Complement Pathway, Classical*
  • HIV Envelope Protein gp120 / metabolism
  • HIV Envelope Protein gp41 / metabolism*
  • HIV-1 / pathogenicity
  • HIV-1 / physiology*
  • Humans
  • Polymyxin B / pharmacology
  • Recombinant Proteins / metabolism

Substances

  • Complement C1
  • HIV Envelope Protein gp120
  • HIV Envelope Protein gp41
  • Recombinant Proteins
  • Polymyxin B