Characterization of B-cell epitopes in the envelope glycoproteins of simian immunodeficiency virus.

We identified previously a neutralizing epitope in the V2 domain of the simian immunodeficiency virus (SIVmac) external envelope protein. The present study reports identification of five additional linear epitopes of SIVmac (isolate 251) by immunological screening of a peptide library expressed in yeast, using SIVmac-infected macaque sera. Three epitopes were localized in the envelope glycoproteins and the two others in the reverse transcriptase and in the Rev regulatory protein. Antibody response against the four envelope epitopes was monitored for 2 years in 12 macaques experimentally infected by SIVmac251. These four envelope regions represent major immunodominant epitopes of the SIVmac. Two epitopes are located in the V3 domain (a.a. 311-330) of the external gp130 and near the amino terminal part (a.a. 601-619) of the transmembrane gp36, in regions similar to those identified in HIVs, demonstrating immunological similarities between the envelopes of SIVs and HIVs. SIV-specific immunodominant epitopes were also identified in the V1 (a.a. 111-130) and V2 (a.a. 171-190) domains of the external gp130. In particular, antibody response against the V2 neutralizing region seems to play some role in the control of disease progression in SIVmac-infected macaques.