Fc receptor-like activity of mouse hepatitis virus E2 glycoprotein

Herpesviral Fcgamma receptors: culprits attenuating antiviral IgG?

Production of IgG in response to virus infection is central to antiviral immune effector functions and a hallmark of B cell memory. Antiviral antibodies (Abs) recognising viral glycoproteins or protein antigen displayed on the surface of virions or virus-infected cells are crucial in rendering the virus noninfectious and in eliminating viruses or infected cells, either acting alone or in conjunction with complement. In many instances, passive transfer of Abs is sufficient to protect from viral infection. Herpesviruses (HV) are equipped with a large array of immunomodulatory functions which increase the efficiency of infection by dampening the antiviral immunity. Members of the α- and β-subfamily of the Herpesviridae are distinct in encoding transmembrane glycoproteins which selectively bind IgG via its Fc domain. The Fc-binding proteins constitute viral Fcγ receptors (vFcγRs) which are expressed on the cell surface of infected cells. Moreover, vFcγRs are abundantly incorporated into the envelope of virions. Despite their molecular and structural heterogeneity, the vFcγRs generally interfere with IgG-mediated effector functions like antibody (Ab)-dependent cellular cytolysis, complement activation and neutralisation of infectivity of virions. vFcγRs may thus contribute to the limited therapeutic potency of antiherpesviral IgG in clinical settings. A detailed molecular understanding of vFcγRs opens up the possibility to design recombinant IgG molecules resisting vFcγRs. Engineering IgG with a better antiviral efficiency represents a new therapeutic option against herpesviral diseases.

Molecular mimicry between Fc receptor and S peplomer protein of mouse hepatitis virus, bovine corona virus, and transmissible gastroenteritis virus

We have previously demonstrated molecular mimicry between the S peplomer protein of mouse hepatitis virus (MHV) and Fc gamma R (Fc gamma R). A monoclonal antibody (MAb) to mouse Fc gamma R (2.4G2 anti-Fc gamma R MAb), purified rabbit immunoglobulin, but not their F(ab')2 fragments, as well as mouse and rat IgG, immunoprecipitated (1) recombinant S peplomer protein expressed by a vaccinia virus recombinant in human, rabbit, and mouse cells, and (2) natural S peplomer protein from cells infected with several strains of MHV and MHV escaped mutants. We report here results of studies documenting molecular mimicry between Fc gamma R and S peplomer protein of viruses representing three distinct antigenic subgroups of the Coronaviridae. We have shown a molecular mimicry between the S peplomer protein of bovine corona virus (BCV) and Fc gamma R. The 2.4G2 anti-Fc gamma R MAb, rabbit IgG, but not its F(ab')2 fragments, as well as homologous bovine serum, free of anti-BCV antibodies, immunoprecipitated S peplomer protein of BCV (Mebus strain). In contrast, we did not find molecular mimicry between S peplomer protein of human corona virus (HCV-OC43) and Fc gamma R. Although the OC43 virus belongs to the same antigenic group as MHV and BCV, MAb specific for human Fc gamma RI or Fc gamma RII and purified human IgG1, IgG2, and IgG3 myeloma proteins did not immunoprecipitate the S peplomer protein from HCV-OC43-infected RD cells. In addition, we did demonstrate molecular mimicry between the S peplomer protein of porcine transmissible gastroenteritis virus (TGEV) and Fc gamma R. TGEV belongs to the second antigenic subgroup of coronaviridae.(ABSTRACT TRUNCATED AT 250 WORDS)

Molecular mimicry between S peplomer proteins of coronaviruses (MHV, BCV, TGEV and IBV) and Fc receptor

In previous studies we have demonstrated molecular mimicry between the S peplomer protein of Mouse Hepatitis Virus (MHV) and Fc gamma Receptor (Fc gamma R) of IgG. Rabbit IgG, but not its F(ab')2 fragments, monoclonal rat and mouse IgG and the rat 2.4G2 anti-mouse Fc gamma R monoclonal antibody (mab) immunoprecipitated natural and recombinant MHV S protein. On the basis of a number of criteria, MHV S peplomer protein exhibits Fc IgG binding ability. We report here a molecular mimicry between the S peplomer protein of Bovine Coronavirus (BCV) and Fc gamma R. BCV S peplomer protein which belongs to the same antigenic subgroup as MHV also binds Fc portion of rabbit IgG and is immunoprecipitated by the 2.4G2 anti-Fc gamma R mab. In contrast, Transmissible Gastroenteritis Coronavirus (TGEV) and Infectious Bronchitis Virus (IBV) S peplomer proteins which represent two distinct antigenic subgroups of Coronaviridae do not bind rabbit IgG and do not react with anti-Fc gamma R mab. However, homologous swine IgG, but not its F(ab')2 fragments, immunoprecipitated from TGEV-infected cells a polypeptide chain with molecular mass of 195 kDa, identical to that immunoprecipitated by the T36 mab anti-TGEV S peplomer protein.

Microheterogeneity of S-glycoprotein of mouse hepatitis virus temperature-sensitive mutants

Mouse hepatitis virus (MHV) strain JHM (MHV-JHM) is a neurotropic coronavirus that causes acute fatal encephalomyelitis in 75-99% of infected mice. The surviving animals may subsequently develop demyelinating disease. We compared the S peplomer protein of the wild type (wt) and five temperature-sensitive (ts) mutants of MHV-JHM. In contrast with the wt, none of these five cause fatal disease (mortality less than 10%). Three of these ts mutants did not induce any demyelinating disease, a fourth caused demyelinating disease in 5% of the animals and a fifth, designated ts8, exhibited strong demyelinating properties and caused demyelination in 99% of the animals. SDS-PAGE analysis revealed no differences in the molecular weight of S peplomer protein of wt or ts MHV-JHM mutants. However, isoelectric focusing of the S protein of these five ts mutants and the wt MHV-JHM, followed by transfer to nitrocellulose sheets and immunoblotting with anti-S specific antibody revealed significant differences in the microheterogeneity of the S protein.