By using GP-specific monoclonal antibodies, several epitopes recognized by ADE antibodies were identified and these epitopes were mostly located in the MLR of the GP1 subunit (Takada et al., 2007; Nakayama et al., 2011) . It should be noted that neutralizing antibodies appear to recognize different epitopes that are not located on the MLR (Takada et al., 2003b; Lee et al., 2008) . As reflected by the high variability of the MLR amino acid sequences and limited overall cross-reactivity of anti-sera among filovirus species (i.e., ZEBOV, SEBOV, CIEBOV, BEBOV, REBOV, and MARV), ADE activities of the anti-sera to GP are virus-species-specific (Takada et al., , 2007 Nakayama et al., 2010) . Interestingly, potential viral pathogenicity is correlated with the ability to induce ADE antibodies, suggesting the possible contribution of ADE to different pathogenicity between filoviruses Nakayama et al., 2011) . More importantly, the demonstration of ADE of filovirus infection raises fundamental questions about the development of GP-based vaccines and the use of anti-GP antibodies for passive immunization.