Interaction ofcomplement andspecific antibodies withtheexternal glycoprotein 120ofHIV-1

SUMMARY Previously we haveinvestigated theinteraction ofhumancomplement aswell as one polyclonal andthree humanmonoclonal antibody preparations withthehumanimmunodeficiency virus type-i(HIV-1) transmembrane recombinant glycoprotein (rgp4l). A strongcompetition was foundbetween theantibodies anddeposited complement proteins forthesame binding sites located within theimmunodominant region ofrgp41. Theaimofthepresent experiments was to seeifthesame typeofantibody-complement-HIV- I interactions could beobserved withtheouter envelope glycoprotein (rgp 120) ofHIV-1.Three different glycosylated rgp120preparations, aswell asa synthetic peptide corresponding totheV3loopoftheMN strain, wereadsorbed toenzymelinked immunosorbent assay (ELISA)plates andincubated withmixtures ofanti-rgp120 antibodies andnormal humanserum(NHS)asacomplement source.Fixedcomplement proteins andantibodies were detected withspecific, peroxidase-labelled antibodies against different complement proteins (Ciq,C4b,C3b)andthey-chain ofantibodies. Intheabsence ofanti-rgpl 20, highamountsofC3weredeposited toeachrgpl20 preparation tested (including theV3peptide) butsignificant differences intheamountsofboundClqandC4bwere observed. Usingsera deficient indifferent complement proteins, we foundthatboththeclassical andthealternative pathways contributed totheC3binding torgp120. Addition ofspecific antibodies didnotincrease complement activation byrgpl20 andonlyinthecaseofa monoclonal antibody totheV3-loop could we seecomplement-dependent inhibition ofantibody binding.