B-cell continuous epitopes of the SIVmac-251 envelope protein in experimentally infected macaques

The humoral immune response of 34 macaques experimentally infected with SIVmac-251 was studied using a combination of an epitope library and synthetic peptides. The course of the immune response was checked for up to 9 months postinfection with a panel of clones expressing SIV fragments. A systematic study was performed with synthetic peptides covering the whole transmembrane (TM) and external (SU) envelope proteins. Seven major immunodominant epitopes were characterized. Four are localized in the SU protein: one in the V1 region (111-130), one in the Cys loop of the V3 region (311-330) and two in the C-terminal end (501-520 and 511-530). Three are localized in the TM protein: one in the extracellular domain (601-619), one in the anchor domain (731-750) and one in the intracytoplasmic domain (861-881). Among these epitopes, only one, 601-619, was found to be reactive with all sera and can be defined as the principal immunodominant epitope.