ANTIBODIES OF SYMPTOMATIC HUMAN-IMMUNODEFICIENCY-VIRUS TYPE 1-INFECTED INDIVIDUALS ARE DIRECTED TO THE V3 DOMAIN OF NONINFECTIOUS AND NOT OF INFECTIOUS VIRIONS PRESENT IN AUTOLOGOUS SERUM

The present study was designed to determine the antibody specificity f or the human immunodeficiency virus type 1 (HIV-1) V3 domains of infec tious and noninfectious virions present in the serum of AIDS patients. To accomplish this, HIV-1 was isolated in the presence of autologous antibodies from the serum samples of six AIDS patients in HIV-1-negati ve donor peripheral blood mononuclear cells by short-term cultivation. The isolated virus, defined as the infectious cell-free virus (iCFV), was characterized by sequence analysis of the proviral DNA coding for the third hypervariable (V3) region of the external glycoprotein gp12 0. This was carried out by amplifying and cloning the V3 region. In al l six cases studied, 20 randomly selected V3 clones derived from the p roviral DNA of the iCFV, 20 clones from patient cell-free virus, and 2 0 clones from cell-integrated virus were sequenced to study the distri bution and frequency of the intrapatient virus population. The number of major virus variants in the six patients ranged from three to nine. The various V3 sequences found in the AIDS patients showed the typica l amino acid pattern of the syncytium-inducing and non-syncytium-induc ing viral phenotypes characteristic for the late stage of infection. H owever, only one patient-specific iCFV variant was detected within the 20 V3 clones analyzed per virus isolation, For the sis patients a tot al of 34 V3-loop variants, either iCFV or non-iCFV, was observed. All 34 V3-loop sequences were expressed as glutathione-S-transferase fusio n proteins (V3-GST). The autologous antibody response to the V3-GST fu sion proteins was studied by Western immunoblot analysis. ri strong an tibody response to almost all non-iCFV V3-GST proteins was found in th e sera of the six patients. In contrast, the autologous antibody respo nse to the sis iCFV V3 loops was undetectable (in four patients) or ve ry faint (in two patients) compared with that to the non-iCFV V3 loops . Five of the sis iCFV loops shelved positively charged amino acids at positions strongly associated with the syncytium-inducing phenotype. These findings suggest that our in vitro isolation system selects for virions which are not recognized by V3-specific antibodies and are inf ectious bath in vitro and in vivo.