Abstract
Ebola virus (EBOV) is a highly virulent human pathogen. Recovery of infected patients is associated with efficient EBOV-specific immunoglobulin G (IgG) responses, whereas fatal outcome is associated with defective humoral immunity. As B-cell epitopes on EBOV are poorly defined, we sought to identify specific epitopes in four EBOV proteins (Glycoprotein (GP), Nucleoprotein (NP), and matrix Viral Protein (VP)40 and VP35). For the first time, we tested EBOV IgG+ sera from asymptomatic individuals and symptomatic Gabonese survivors, collected during the early humoral response (seven days after the end of symptoms) and the late memory phase (7–12 years post-infection). We also tested sera from EBOV-seropositive patients who had never had clinical signs of hemorrhagic fever or who lived in non-epidemic areas (asymptomatic subjects). We found that serum from asymptomatic individuals was more strongly reactive to VP40 peptides than to GP, NP or VP35. Interestingly, anti-EBOV IgG from asymptomatic patients targeted three immunodominant regions of VP40 reported to play a crucial role in virus assembly and budding. In contrast, serum from most survivors of the three outbreaks, collected a few days after the end of symptoms, reacted mainly with GP peptides. However, in asymptomatic subjects the longest immunodominant domains were identified in GP, and analysis of the GP crystal structure revealed that these domains covered a larger surface area of the chalice bowl formed by three GP1 subunits. The B-cell epitopes we identified in the EBOV VP35, VP40, NP and GP proteins may represent important tools for understanding the humoral response to this virus and for developing new antibody-based therapeutics or detection methods.
Highlights
Ebola virus (EBOV), a member of the Filoviridae family, is a highly virulent pathogen for humans and nonhuman primates [1]
Defective adaptive immunity observed in fatal cases is associated with an impaired humoral response, as EBOV-specific immunoglobulin G (IgG) and IgM are barely detectable before death [12,13,14]
None of the peptides was recognized by all of the survivor group #1 and #2 sera, but GP peptide 78, NP peptide 105 and VP40 peptides 73 and 77 reacted with more than half of the group #1 sera. These peptides composed several linear regions which were similar during the three EBOV outbreaks that occurred in Gabon between 1996 and 2001
Summary
Ebola virus (EBOV), a member of the Filoviridae family, is a highly virulent pathogen for humans and nonhuman primates [1]. Fatal EBOV infection is characterized by a defective innate immune response, leading to uncontrolled release of inflammatory mediators and chemokines in the late stage of the disease, and correlates with the collapse of adaptive immunity with massive T and B lymphocyte apoptosis [8,9,10]. Defective adaptive immunity observed in fatal cases is associated with an impaired humoral response, as EBOV-specific IgG and IgM are barely detectable before death [12,13,14]. Recovery is associated with early, increasing levels of long-lasting EBOV-specific IgG, followed by viral antigen clearance [12,15,16]. Moderate amounts of EBOV-specific IgG are detected about 3 weeks after infection in asymptomatic patients [8]. A strong early humoral response may play a major role in survival
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