HIV type 1 subtype E-infected patients with broadened, dual (B/E) V3 loop serology have increased cross-neutralizing antibodies.

The two prevalent subtypes of HIV-1 circulating in Thailand are subtypes E and B. While the most prevalent subtype continues to be E using molecular typing assays, immunologically, a subset of subtype E-infected patients (3.4% in 1997) have binding antibodies to both the E and B V3 loops in a peptide ELISA. To assess the potential function of this dual (B/E) V3 reactivity, plasmas from patients with genetically defined HIV-1 subtype E infection and either E or B/E V3 serotypes were compared for magnitude and breadth of neutralization of seven primary and laboratory-adapted subtype B and E viruses. Dually reactive (B/E) plasmas showed significantly increased cross-neutralizing activity against subtype B viruses (p < 0.001), and increased neutralization of the panel of viruses overall (p < 0.02), as compared to monoreactive E serotype plasmas. While the total envelope binding antibody titers to both subtype B and E envelopes did not differ significantly between the E and B/E plasmas, 67% of B/E plasmas neutralized >50% of the viruses in the panel, and only 14% of E plasmas showed this broadened neutralizing activity. These data suggest that dual (B/E) V3 loop reactivity may be a marker of broader immune recognition of HIV envelope epitopes in subtype E-infected patients. V3 loop antibody, perhaps in conjunction with antibodies to additional epitopes, may play a role in neutralization of virus isolates from Thailand.