Tina M Cairns
| Tina M Cairns |
Tina M Cairns1, Huan Lou1, Lauren M Hook3, Doina Atanasiu1, Wan Ting Saw1, Tomas Bergstrom1, Harvey M Friedman3, Gary H Cohen1
1Basic & Translational Sciences, University of Pennsylvania, 2Infectious Diseases, University of Gothenberg; 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.