Infection of RAW 264.7 Cells by Murine Leukemia Virus-Derived Retroviral Pseudotype Expressing the Envelope Glycoprotein of EBOV Is Enhanced by Antibodies.

It has been shown that antibodies can enhance Ebola virus (EBOV) infection at sub-neutralizing concentrations. The effect of antibodies on the infection of murine cell line (RAW 264.7) with MLV-EBOV, a murine leukemia virus pseudotype expressing surface glycoprotein (GP) of EBOV and green fluorescent protein (GFP) has been studied. Moreover, regions of EBOV GP targeted by antibodies enhancing the infection have been investigated. Serum and monoclonal antibodies (mAbs) were obtained from mice inoculated with MLV-EBOV. Plasma from patients and humanized anti-EBOV GP mAbs were obtained. The proportion of GFP-positive cells was determined by FACS analysis. Trypsin-digested EBOV GP was incubated in affinity columns prepared with mAbs. Eluted peptides were analyzed by high-resolution mass spectrometry. The infection of cells with MLV-EBOV was enhanced by immune mouse serum, human plasma and mAbs. The infection was the result of interactions between MLV-EBOV/antibody complexes and FcγRs. Regions of EBOV GP, located in GP1 core, furin cleavage site, N-terminal part of GP2, and HR1 and HR2 domains are target of antibodies able to enhance the infection. In conclusion, the RAW 264.7 cell line associated with MLV-EBOV can be used to study the enhancing activity of murine and human antibodies and may help to select antibodies or vaccine formulations that do not lead to enhancement of EBOV infection.