Using sera from volunteers in a DENV1 monovalent vaccine trial, we found that neutralization of strain TVP2130 was similarly impacted by mutation at E residues 126 and 157, while mutation of these residues in strain 16007 did not markedly change neutralization sensitivity. genotype 2 strain 16007 did not markedly change neutralization sensitivity, Firategrast (SB 683699) indicating the existence of additional DENV1 type-specific antibody targets. The accessibility of antibody epitopes can be strongly influenced by the conformational dynamics of virions and modified allosterically by amino acid variation. FLJ34064 We found that changes at E Firategrast (SB 683699) domain II residue 204, shown previously to impact access to a poorly accessible E domain III epitope, impacted sensitivity of DENV1 16007 to neutralization by vaccine immune sera. Our data identify a role for minor sequence variation in changes to the antigenic structure that impacts antibody recognition by polyclonal immune sera. Understanding how the many structures sampled by flaviviruses influence antibody recognition will inform the design and evaluation of DENV immunogens. IMPORTANCEDengue virus (DENV) is an important human pathogen that cocirculates globally as four serotypes. Because sequential infection by different DENV serotypes is associated with more severe disease, eliciting a protective neutralizing antibody response against all four serotypes is a major goal of vaccine efforts. Here, we report that neutralization of DENV serotype 1 by polyclonal antibody is impacted by minor sequence variation among virus strains. Our data suggest that mechanisms that control neutralization sensitivity extend beyond variation within antibody epitopes but also include the influence of single amino acids on the ensemble of structural states sampled by structurally dynamic virions. A more detailed understanding of the antibody targets of DENV-specific polyclonal sera and factors that govern their access to antibody has important implications for flavivirus antigen design and evaluation. KEYWORDS:dengue virus, humoral immunity, neutralizing antibody, polyclonal antibody, structural dynamics, vaccines == INTRODUCTION == Dengue virus (DENV) is a globally important human pathogen responsible for an estimated 105 million infections per year (1). It is predicted that 2.5 billion people live at risk of DENV infection due to the extensive Firategrast (SB 683699) geographical range of theAedesmosquito vector responsible for virus transmission. While most DENV infections do not cause disease, clinical manifestations arising from infection with one of the four serotypes of DENV range from a mild febrile illness to potentially life-threatening complications, including plasma leakage and shock, severe bleeding, and organ involvement (referred to as severe dengue) (2). Because more severe disease manifestations are most frequently associated with secondary infections by a heterologous DENV serotype (3,4), vaccine efforts are focused on a tetravalent platform that elicits neutralizing antibodies against all four DENV serotypes. A chimeric yellow fever virus (YFV)-DENV live attenuated tetravalent vaccine developed by Sanofi-Pasteur (CYD-TDV; Dengvaxia) was recently licensed (5). However, unequal protection was observed against the four serotypes in phase III human clinical trials (68). This vaccine is not recommended for children under the age of 9 due to evidence that it may predispose younger, seronegative recipients to severe disease upon subsequent DENV infection (7,9,10). Thus, the need to control primary DENV infections remains unmet. Two additional tetravalent live-attenuated candidates are currently in phase III clinical trials (NCT02406729[NIAID] andNCT02747927[Takeda]). A member of the genusFlavivirus, DENV has an 11-kb single-stranded RNA genome that is translated as a single polyprotein and cleaved into three structural proteins (capsid [C], premembrane [prM], and envelope [E]) and at least seven nonstructural proteins (11). Noninfectious, immature virions bud into the endoplasmic reticulum (ER) and incorporate 180 copies of the E protein, arranged as 60 heterotrimeric spikes associated with an equal number of prM Firategrast (SB 683699) proteins (12,13). As virus particles traffic through the trans-Golgi network, low-pH-induced structural rearrangements reveal a host-furin protease recognition site in prM, enabling cleavage. A short membrane-bound M protein remains associated with the virus, while the cleaved pr portion dissociates at neutral pH upon release from the cell (14,15). The resulting mature flavivirus virions are smooth, spherical particles incorporating 90 sets of anti-parallel E homodimers arranged in a.