Serum enhancement of human immunodeficiency virus (HIV) infection correlates with disease in HIV-infected individuals.

The sera from 16 individuals infected with the human immunodeficiency virus (HIV) at different clinical stages were evaluated for antibody-dependent neutralization and/or enhancement of infectivity by HIV. The HIV isolate from each individual (homotypic) and established laboratory strains showing broad cellular host range and cytopathicity were used. All sera could neutralize one of the laboratory-passaged isolates, whereas only two could neutralize the corresponding homotypic strain. Seven homotypic isolates were enhanced by serum from the respective individual. This activity was primarily observed in patients with acquired immune deficiency syndrome. Moreover, the tropism for macrophages of four of these seven viral isolates was found to be enhanced by the homotypic sera. Finally, sequential pairs of HIV and sera obtained from five HIV-infected individuals with different clinical progression were studied over time. The enhancing activity of three of the five sera appeared to increase over time, indicating changes in both the host virus population and the type of antibodies produced. These results suggest that enhancing antibodies contribute to the spread and pathogenesis of HIV in vivo. They emphasize the necessity of studying further the association of enhancing antibodies and disease progression in infected individuals.