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MHV S peplomer protein expressed by a recombinant vaccinia virus vector exhibits IgG Fc-receptor activity
E L Oleszak1, S Perlman, J L Leibowitz
1Department of Pathology and Laboratory Medicine, University of Texas Health Science Center, Houston 77030.
Abstract:
We have previously shown that cells infected with mouse hepatitis virus (MHV) bind rabbit, mouse, and rat IgG by the Fc portion of the IgG molecule. This Fc-binding activity appeared to be mediated by the MHV S protein. S protein could also be precipitated from MHV-infected cells by a monoclonal antibody directed against the murine Fc gamma receptor (Fc gamma R). To prove definitively that the S protein mediates Fc-binding activity, we have expressed the MHV S protein utilizing recombinant vaccinia viruses. The anti-Fc gamma R monoclonal antibody, 2.4G2, precipitated recombinant S protein in cells of murine, human, and rabbit origin. Since the anti-Fc receptor monoclonal antibody does not react with human and rabbit Fc receptors these results demonstrate that the epitope recognized by this antibody is carried on the MHV S protein and is not murine in origin. Examination of various MHV isolates and escape mutants failed to identify the precise sequences in S responsible for the molecular mimicry of the murine Fc gamma R. These data are consistent with the hypothesis that a previously identified region of similarity between the S protein and the Fc gamma R mediates this activity. The Fc binding activity of S was expressed on the cell surface, since MHV-JHM-infected cells, but not uninfected cells, formed rosettes with anti-sheep red blood cell (SRBC) antibody-coated SRBC. The anti-Fc gamma R monoclonal antibody neutralized MHV-JHM and inhibited syncytium formation induced by the MHV S protein.
Insights
Mouse hepatitis virus (MHV) S protein binds IgG via Fc, mimicking murine Fc gamma receptors. This mimicry, mediated by the S protein, is crucial for MHV infection and pathogenesis.
Area of Science:
- Virology
- Immunology
- Molecular Biology
Background:
- Cells infected with mouse hepatitis virus (MHV) exhibit Fc-binding activity, interacting with IgG molecules through their Fc portion.
- This Fc-binding activity was previously hypothesized to be mediated by the MHV S protein, potentially mimicking host Fc gamma receptors.
Purpose of the Study:
- To definitively prove that the MHV S protein mediates Fc-binding activity.
- To investigate the molecular mimicry of murine Fc gamma receptors by the MHV S protein.
Main Methods:
- Expression of the MHV S protein using recombinant vaccinia viruses in murine, human, and rabbit cells.
- Precipitation of recombinant S protein using a monoclonal antibody against murine Fc gamma receptor (Fc gamma R).
- Rosette formation assays with MHV-JHM-infected cells and antibody-coated sheep red blood cells (SRBC).
- Neutralization assays using anti-Fc gamma R monoclonal antibody on MHV-JHM.
Main Results:
- Recombinant MHV S protein was precipitated by anti-Fc gamma R monoclonal antibody in cells of various origins, demonstrating an epitope on the S protein itself.
- Fc binding activity of S protein was expressed on the cell surface, as evidenced by rosette formation.
- Anti-Fc gamma R monoclonal antibody neutralized MHV-JHM and inhibited syncytium formation.
Conclusions:
- The MHV S protein directly mediates Fc-binding activity, mimicking host Fc gamma receptors.
- The identified epitope recognized by the anti-Fc gamma R antibody is on the S protein, not a host receptor.
- This molecular mimicry likely plays a significant role in MHV pathogenesis.