REV genome consists of three structural genes (gag, pol and env) flanked by long-terminal repeats (LTRs) [10] . The major mature env gene products of REVs are the surface glycoprotein (gp90) and the transmembrane protein (gp20) [11, 12] . The gp90 protein containing both continuous and discontinuous epitopes functions as the immunodominant protein [13] and is responsible for eliciting REV antibodies. Previous studies indicated that the Cterminal epitope of gp90 was exposed on the outer surface of the REV-A-infected cell [12] . However, the epitope identified in REV gp90 protein has not been finely mapped, and the core sequence of the epitope needs to be determined.