ANALYSIS OF NEUTRALIZING AND ENHANCING ANTIBODIES TO HUMAN-IMMUNODEFICIENCY-VIRUS TYPE-1 PRIMARY ISOLATES IN PLASMA OF INDIVIDUALS INFECTEDWITH ENV GENETIC SUBTYPE-B AND SUBTYPE-E VIRUSES IN THAILAND

Twenty-seven HIV-1 isolates were obtained from 51 asymptomatic HIV-1-i nfected pregnant women or intravenous drug users (IDUs) in Bangkok. Us ing heteroduplex mobility assay (HMA), it was found that the majority of the HIV-1 isolates (9 out of 11) from pregnant women belonged to ge netic subtype E, whereas most of the subtype B HIV-1 isolates (15 out of 16) were isolated from IDUs. The HIV-1 isolates were tested for the ir susceptibility to neutralization or antibody-dependent enhancement with homologous and heterologous plasma of the two different genetic s ubtypes, B and E. Overall, HIV-1 neutralizing activity could be found in 37.3% of virus/plasma pairs for both subtypes B and E. No significa nt correlation could be identified between the two genetic subtypes (B and E) and their susceptibility to neutralization. Subtype B plasma d emonstrated frequent cross-neutralization of subtype E viruses in 38.5 % of virus/plasma pairs, whereas cross-neutralization activity of subt ype E specific plasma samples was more limited and could cross-neutral ize subtype B viruses only in 15.8% of cases. Some of the viral strain s independently of their genetic subtypes were more susceptible to neu tralization by plasma specific for both subtype E or subtype 11, sugge sting that this phenomenon is related to the proper biological propert ies of a viral strain. Antibody-dependent enhancement of HIV-1 strains could be detected in 12/83 (14.5%) virus-plasma pairs irrespective of genetic subtypes. Similar to neutralization results, the HIV-1 enhanc ing activity of plasma was mostly isolate-specific. The HIV isolates t hat were susceptible to neutralization were not enhanced by any plasma . On the other hand, the HIV isolates that were enhanced by plasma wer e resistant to neutralization in most cases. Such a dissociation betwe en susceptibility to neutralization or enhancement may be indicative o f the existence of discrete epitopes determining the two distinct vira l properties.