From the neutralizing MAbs from donor 013 that bound to rE, some bound to the lateral ridge and A strand epitopes on EDIII (ref) . We also identified several neutralizing hMABs (35.3, 18.21, 13.6, 23.13 ) that bound to rE but not EDIII and these antibodies most likely bind to epitopes on EDI or EDII. We are especially interested in mapping the binding sites of these hMABs as recent studies indicate that epitopes other than the lateral ridge and A strand of EDIII can be the targets of strongly neutralizing mouse, horse and primate antibodies [29, 37, 38, 7, 22] , Our results indicating that prM was a dominant target of the primary antibody response are in agreement with other recent studies [25, 30] . The prM protein is required for the proper folding and assembly of flavivirus particles in the endoplasmic reticulum [39] , while also preventing adventitious fusion of the virus [40] in the acidic environment of the trans-Golgi network. Recent studies have demonstrated that DENV virions produced in cell culture are often partially processed and contain a mixture of unprocessed prM and fully processed M [41] . The maturation state and relative amount of prM on a virion can alter the potency of antibodies that bind specific epitopes on E, including the cross-reactive antibodies that bind the fusion loop in DII [42] . Additionally, immature, noninfectious particles became infectious in the presence of prM antibody by enhancing the ability of immature dengue virions to infect Fc-receptor bearing cells in vitro [25, 43] . Given our findings and those of others [25] establishing that prM antibodies are common following primary and secondary DENV infections, more work needs to be performed to address their contribution to dengue pathogenesis in humans.