Endogenous anti-Ebola virus GP 1,2 antibodies interfere with detection of secreted glycoprotein in the blood of EVD patients

ABSTRACT Ebola disease (EBOD) is a highly infectious disease with severe hemorrhagic symptoms. It is caused by orthoebolaviruses , which include the Ebola virus ( Orthoebolavirus zairense ) (EBOV) causing Ebola virus disease (EVD), the most lethal EBOD to humans. Through co-transcriptional polymerase stuttering and subsequent proteolytic processing, its GP gene produces multiple protein products, including secreted glycoprotein (sGP) and structural membrane-associated trimeric GP 1,2 . Although sGP is known to circulate in the blood, its physiological significance in disease pathology remains speculative. We quantified sGP using enzyme-linked immunosorbent assay (ELISA) in 36 acute human EVD cases from the 10th and 11th EVD outbreaks in the Democratic Republic of the Congo (DRC) using single-time-point biobanked samples. We detected and quantified sGP in four patients with strong GP gene transcription (GP Ct < 25), as evidence of viral replication, but with no endogenous anti-EBOV GP 1,2 IgG. However, sGP was not quantified in patients with lower GP transcription (Ct > 25), regardless of their anti-EBOV GP 1,2 IgG results. While two patients, MAM179 and MAM271, had notably strong GP transcription (Ct < 25), their high amounts of endogenous anti-EBOV GP 1,2 IgG might have interfered with detection by the assay detection antibody, a human anti-EBOV GP 1,2 /sGP IgG. Furthermore, the addition of sera containing anti-EBOV GP 1,2 IgG reduced the binding between sGP and anti-EBOV GP 1,2 /sGP used as detection antibodies. This suggested that the level of sGP in circulation is strongly linked to the intensity of GP transcription. Additionally, circulating sGP in this context would form complexes with anti-GP 1,2 antibodies, hence hindering additional antibody binding for detection. IMPORTANCE Insight into the mechanism of immune function by the Ebola virus secreted glycoprotein (sGP) in humans is essential for better understanding viral pathogenesis, immune protection, and immune evasion strategies. Research utilizing samples from patients who are infected with or have survived infection with the Ebola virus offers an unparalleled opportunity to determine the immunological significance of sGP. This research evaluates, in acutely infected patients from Ebola virus disease outbreaks, the role of EBOV sGP in modulating antibody responses directed against viral entry glycoprotein. By elucidating how sGP influences antibody-mediated immunity, the study advances our understanding of a conserved immune-evasion mechanism shared across all orthoebolaviruses. These investigations are valuable resources for designing more efficacious vaccines, therapies, and biomarkers for monitoring Ebola virus diseases.