An antigenic and kinetic comparison of IgG Fc binding to the HSV-1 and HSV-2 gE/gI protein complex using surface plasmon resonance



Tina M. Cairns

Cairns, Tina M.1, Lou, Huan1, Atanasiu, Doina1, Saw, Wan Ting1, Hook, Lauren M.3, Bergstrom, Tomas2, Friedman, Harvey M.3, Cohen, Gary H.1
1University of Pennsylvania School of Dental Medicine, Department of Basic and Translational Sciences
2University of Gothenburg, Infectious Diseases
3University of Pennsylvania Perelman School of Medicine

Introduction

HSV gE/gI exists in the virion envelope and infected cell membranes as a non-covalent complex and is associated with Fc binding and virus-cell spread. gE/gI immune activity is mediated by its capacity to block IgG Fc-mediated complement activation and antibody-dependent cell-mediated cytotoxicity.

Methods

We developed an Fc binding assay using surface plasmon resonance (SPR) and baculovirus-produced gE1, gE2, gE/gI1, and gE/gI2.

Results

Unlike gE1, binds poorly to human/rabbit IgG Fc. We questioned whether the gE/gI2 complex, as originally found for gE/gI1, may be critical for proper type-2 Fc binding. Overall, gE production is highly dependent on the co-expression with gI. We found that formation of the gE/gI2 complex now allows Fc binding and, importantly, stabilizing the Fc-gE/gI complex. Thus, as previously shown for type-1, a gE/gI complex enhances Fc binding over the single gE partner. Compared to gE/gI1, the kinetics of IgG binding for gE/gI2 were different (faster on- and off-rates). We set out to localize the Fc binding region on gE/gI2 and to develop an Fc blocking assay. We tested several anti-gE monoclonal antibodies (MAbs) for their ability to block gE1-IgG or gE/gI-IgG binding. Using SPR, we found a type-common MAb that completely blocked the binding of IgG to gE1, gE/gI1, and gE/gI2, while other anti-gE MAbs had no effect on IgG binding. The blocking antibody epitope is completely within the gE molecule; it is not dependent on gI1 or gI2 for antibody binding and it is conformationally-dependent.

Conclusion

The data suggest that gI contributes to the stabilization of gE/gI-Fc binding in both serotypes although the kinetics between serotypes remain different. Fc binding can be blocked by specific anti-gE MAbs.