More generally, these findings highlight the potential for a single antigenic site to elicit diverse Ab responses that vary in binding mode, mechanisms of action, and potency. mechanisms despite sharing an epitope. Delineating the full range of Ab binding modes and neutralization mechanisms against a single epitope may inform therapeutic approaches and refine vaccine design. Keywords: Dengue virus, E dimer epitope, antibody valency, broadly neutralizing antibodies, virus neutralization Introduction The goal of many vaccines is to elicit antibodies (Abs) with the capacity to protect against future infection. Rational vaccine design strategies first identify epitopes targeted by potent Abs that are representative of a desired Ab response, and vaccine immunogens are then engineered with the goal of driving Ab responses towards these epitopes (Rappuoli et al., 2016). An important property of IgG Ab molecules and the B cell receptors (BCRs) from which they develop is their ability to engage antigen (Ag) targets bivalently. Avid interactions Bax inhibitor peptide, negative control decrease the concentration of Ab required for neutralization (Klein and Bjorkman, 2010), and Ab crosslinking, the formation of multiple binding interactions between multivalent Ags and one or more Abs, increases the efficiency of immune complex formation (Steensgaard and Johansen, 1980) as well as recruitment of effector cells (Klaassen et al., 1988). It has been demonstrated that some Abs may even depend on bivalent engagement for their antiviral activity against viral targets, as monovalent Ab fragments (Fabs) derived from otherwise potent Abs exhibit marked losses in neutralization potency. For example, poliovirus:Ab complexes regain infectivity upon papain digestion (Icenogle et al., 1983), and monoclonal Abs (mAbs) against Influenza exhibit up to three orders of magnitude 1912-fold losses in neutralization potency upon conversion to Fabs Bax inhibitor peptide, negative control (Schofield et al., 1997). Thus, given the potential requirement for multivalent Ab engagement, vaccine design strategies may need to consider displaying arrays of Ags or epitopes with geometries compatible of inducing bivalent Ab interactions where necessary. While the regular array of Ags on many viral and bacterial species is amenable to Ab crosslinking via multivalent interactions, in some cases Ag arrangement may prohibit bivalent Ab binding. For example, the density of the human immunodeficiency virus-1 (HIV-1) envelope trimer spike estimated to be remarkably low at 7-14 spikes per virion (Zhu et al., 2006). Due to this low spike density, the large physical distance between Env trimers inhibits bivalent Ab binding because the wingspan between IgG arms may not be sufficient to crosslink epitopes within a trimer or bridge multiple trimers (Klein and Bjorkman, 2010). Avidity of Ab binding may be modulated by changing Ag density or placement (Hadzhieva et al., 2017), or by altering physical characteristics of the IgG, with potential consequences for Ab activity (Bournazos et al., 2016). Indeed, it has been demonstrated that endowing Abs with the capacity to bind the HIV-1 envelope trimer bivalently can dramatically boost neutralization potency by introducing a second epitope in a single envelope trimer spike (Wang and Yang, 2010), or by synthetically increasing Fab-Fab distance (Galimidi et al., 2015). Thus, antiviral activity can be improved upon by introducing or enhancing valency effects, and understanding the limits of Ab bivalency may enable improvement in Ab activity for cases where Rabbit Polyclonal to ETV6 bivalent binding is natively unlikely or impossible. In contrast to the sparsity of HIV-1 envelope trimer spikes, a complete shell of envelope (E) proteins fully encapsulates viruses of the family including West Nile Virus (WNV), Japanese Encephalitis Virus (JEV), Zika Virus (ZIKV) and Dengue virus (DENV), which encompasses four distinct serotypes (DENV1-4). In mature DENV (and other flavivirus) virions, the E protein coat consists of 180 E proteins forming 90 E dimers which are arrayed in a unique herringbone pattern Bax inhibitor peptide, negative control across the entire virion surface with quasi-icosahedral geometry (Kuhn et al., 2002). Yet, axes of 2-, 3-, and 5-fold symmetry result in nonuniform local environments at each axis, perhaps accounting for the apparent rarity of Abs targeting DENV via bivalent interactions despite a dense array of Ag (Edeling et al., 2014). This unique arrangement of E proteins on DENV virions may contribute to the virus evasion of potent, bivalent Ab recognition, presenting a hurdle for DENV vaccine strategies where potently neutralizing Ab responses are desired. Non-neutralizing Ab responses or Abs present at sub-neutralizing concentrations have the potential to exacerbate DENV infection by a process termed Ab-dependent enhancement (ADE) (Halstead, 2003). Associated with severe disease more frequently observed with secondary heterotypic infection, ADE is precipitated by Fc receptor (FcR) binding of opsonized but not neutralized virus by, thus enabling efficient infection of FcR-bearing cells (Halstead, 2003). Therefore, the elicitation of potent and cross-neutralizing or broadly neutralizing Ab (bnAb) responses may be required of a DENV vaccine in order to minimize potential risks associated with vaccination. Human bnAbs targeting a conserved epitope at.