title: Human immunodeficiency virus type 1 activates the classical pathway of complement by direct C1 binding through specific sites in the transmembrane glycoprotein gp41.
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.
authors.affiliation: Institut für Hygiene, Innsbruck, Austria.
authors.forename: C F
authors.initials: CF
authors.lastname: Ebenbichler
authors.forename: N M
authors.initials: NM
authors.lastname: Thielens
authors.forename: R
authors.initials: R
authors.lastname: Vornhagen
authors.forename: P
authors.initials: P
authors.lastname: Marschang
authors.forename: G J
authors.initials: GJ
authors.lastname: Arlaud
authors.forename: M P
authors.initials: MP
authors.lastname: Dierich
mesh_terms: D001665:Binding Sites; D003172:Complement C1 / Q000378:metabolism*; D003171:Complement Pathway, Classical; D015699:HIV Envelope Protein gp120 / Q000378:metabolism; D015700:HIV Envelope Protein gp41 / Q000378:metabolism*; D015497:HIV-1 / Q000472:pathogenicity / Q000502:physiology*; D006801:Humans; D011112:Polymyxin B / Q000494:pharmacology; D011994:Recombinant Proteins / Q000378:metabolism
chemical_list: D003172:Complement C1; D015699:HIV Envelope Protein gp120; D015700:HIV Envelope Protein gp41; D011994:Recombinant Proteins; D011112:Polymyxin B