HUMORAL RESPONSE TO OLIGOMERIC HUMAN-IMMUNODEFICIENCY-VIRUS TYPE-1 ENVELOPE PROTEIN

The humoral immune response to human immunodeficiency virus type 1 (HI V-1) is often studied by using monomeric or denatured envelope protein s (Env), However, native HIV-1 Env complexes that maintain quaternary structure elicit immune responses that are qualitatively distinct from those seen with monomeric or denatured Env, To more accurately assess the levels and types of antibodies elicited by HIV-1 infection, we de veloped an antigen capture enzyme-linked immunosorbent assay using a s oluble, oligomeric form of HIV-1(IIIB) Env (gp140) that contains gp120 and the gp41 ectodomain. The gp140, captured by various monoclonal an tibodies (MAbs), retained its native oligomeric structure: it bound CD 4 and was recognized by MAbs to conformational epitopes in gp120 and g p41, including oligomer-specific epitopes in gp41, We compared the rea ctivities of clade B and clade E serum samples to captured Env prepara tions and found that while both reacted equally well with oligomeric g p140, clade B seras reacted more strongly with monomeric gp120 than di d clade E samples, However, these differences were minimized when gp12 0 was captured by a V3 loop MAb, which may lead to increased exposure of the CD4 binding site, We also measured the ability of serum samples to block binding of MAbs to epitopes in gp120 and gp41, Clade B serum samples consistently blocked binding of oligomer-dependent MAbs to gp 41 and, to a slightly lesser extent, MAbs to the CD4 binding site in g p120, Clade E serum samples showed equivalent or greater blocking of o ligomer-dependent gp41 antibodies and considerably less blocking of CD 4-binding-site MAbs, Finally, we found that <5% of the antibodies in c lade B sera bound to epitopes present only in monomeric gp120, 30% bou nd to epitopes present in both monomeric gp120 and oligomeric gp140, a nd 70% bound to epitopes present in oligomeric gp140, which includes g p41. Thus, captured oligomeric Env closely reflects the antigenic char acteristics of Env protein on the surface of virions and infected cell s, retains highly conserved epitopes that are recognized by antibodies raised against different clades, and makes it possible to detect a mu ch greater fraction of total anti-HIV-1 Env activity in sera than does native monomeric gp120.