Maturation of West Nile virus modulates sensitivity to antibody-mediated neutralization

West Nile virions incorporate 180 envelope (E) proteins that orchestrate the process of virus entry and are the primary target of neutralizing antibodies. The E proteins of newly synthesized West Nile virus (WNV) are organized into trimeric spikes composed of pre-membrane (prM) and E protein heterodimers. During egress, immature virions undergo a protease-mediated cleavage of prM that results in a reorganization of E protein into the pseudo-icosahedral arrangement characteristic of mature virions. While cleavage of prM is a required step in the virus life cycle, complete maturation is not required for infectivity and infectious virions may be heterogeneous with respect to the extent of prM cleavage. In this study, we demonstrate that virion maturation impacts the sensitivity of WNV to antibody-mediated neutralization. Complete maturation results in a significant reduction in sensitivity to neutralization by antibodies specific for poorly accessible epitopes that comprise a major component of the human antibody response following WNV infection or vaccination. This reduction in neutralization sensitivity reflects a decrease in the accessibility of epitopes on virions to levels that fall below a threshold required for neutralization. Thus, in addition to a role in facilitating viral entry, changes in E protein arrangement associated with maturation modulate neutralization sensitivity and introduce an additional layer of complexity into humoral immunity against WNV

Agriculture driven nitrogen wet deposition in a karst catchment in southwest China

Nitrogen (N) deposition plays a key role in ecosystem function as one of the major N sources for natural vegetation, particularly in karst agricultural areas with thin soil cover, which drive the karst N fate via rainwater. To understand the seasonal and spatial variation in nitrogen deposition and to identify the major sources of nitrate in wet deposition in a karst agricultural area (Houzhai Catchment) in southwestern China, two sites with different land use were selected to assess wet and dry deposition for one year. Houzhai village (HZV) is an area highly influenced by agriculture, whereas Muzhu reservoir (MZR) is a more pristine environment with less anthropogenic influence. Nitrogenous species and dual nitrate isotopes were analyzed. The results showed that agriculture-derived NH4 + was the major contributor of annual total wet N deposition (> 55 %). The contribution of NH4 + to wet N deposition was 1.63 times higher than that of NO3 − and dissolved organic nitrogen (DON). The annual nitrogen deposition in this study was approximately twice as much as the average wet N deposition over China, while lower dry N deposition relative to other Chinese monitoring sites was observed. The δ15N-NO3 − showed a seasonal trend of negative summer values and positive winter values, which were primarily controlled by the variations in NOx emission sources. Seasonal variation in δ18O-NO3 − was mainly controlled by NOx oxidation pathways and showed a similar trend to δ15N-NO3 −. The contributions from four endmembers (coal combustion, vehicle exhaust, biomass burning, and soil emission) were calculated using a stable isotope mixing model. Contributions show a clear seasonal variation (except vehicle exhaust), with the four sources accounting for 20.0 %, 25.6 %, 22.9 % and 31.5 % respectively (annual mean probability estimate, AMPE) at HZV, and 19.0 %, 27.8 %, 23.2 % and 30.0 % (AMPE) at MZR. Isotopic evidence determined agricultural soil emission is a major contributor to rainwater during the summer growing season, which can significantly impact the agricultural ecosystem