Characterization of human antibodies against envelope protein of dengue virus during natural infection

Abstract

Despite decades of research to develop vaccines against dengue virus (DENV), there is no licensed dengue vaccine available, partly due to the lack of understanding of immune correlates of protection during natural infection. While neutralizing antibodies (Abs) against the envelope (E) protein of DENV are known to be protective, the role of different categories of anti-E Abs in protection and their epitopes remain unknown. The long-term goal of this study is to facilitate the development of a safe and effective dengue vaccine. The objective of the study is to elucidate the categories and epitopes of human anti-E Abs that account for neutralization during natural DENV infection. We hypothesize that after primary DENV infection, type-specific (TS) anti-E Abs are responsible for neutralization against the infecting serotype; after a secondary DENV infection, group-reactive (GR) anti-E Abs, the major component of cross-reactive Abs, correlate with neutralization against the non-exposed serotypes. In the first aim, we defined the role of TS anti-E Abs after primary DENV infection. We demonstrated that TS, rather than cross-reactive, anti-E Abs were responsible for the neutralizing activity and recognized structurally complex epitopes present on the virus particles rather than solubilized E protein. Moreover, we found that domain III of the E protein, though not the predominant epitope, was recognized by TS neutralizing Abs. In the second aim, we investigated the role of GR anti-E Abs in the neutralizing activity against non-exposed serotypes after secondary DENV infection. We demonstrated that the GR monoclonal antibodies derived from individuals with secondary DENV infection had stronger binding avidity and neutralization potency than those from individuals with primary infection, and blocked DENV at post-attachment step. This suggested that dengue immune status of the host (primary versus secondary DENV infection) affects the quality of cross-reactive Abs. In addition, we found that in the sera of 29 patients with secondary DENV infection from a Nicaraguan cohort, the concentration of antifusion loop Abs, which represents GR anti-E Abs, did not correlate with neutralization titers against the current infecting DENV serotype but correlated with neutralization titers against the non-exposed serotypes.