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Efficient neutralization of foot-and-mouth disease virus by monovalent antibody binding
N Verdaguer1, I Fita, E Domingo
1Centre de Investigació i Desenvolupament (CSIC), Barcelona, Spain.
Abstract:
Neutralization of an aphthovirus by monovalent binding of an antibody is reported. Foot-and-mouth disease virus (FMDV) clone C-S8c1 was neutralized by monoclonal antibody (MAb) SD6, which was directed to a continuous epitope within a major antigenic site of the G-H loop of capsid protein VP1. On a molar basis, the Fab fragment was at most fivefold less active in neutralization than the intact antibody, and both blocked virus attachment to cells. Neither the antibody nor the Fab fragment caused aggregation of virions, as evidenced by sucrose gradient sedimentation studies of the antibody-virus complex formed at antibody to virion ratios of 1:50 to 1:10,000. The results of neutralization of infectivity and of ultracentrifugation are fully consistent with structural data based on X-ray crystallographic and cryoelectron microscopy studies, which showed monovalent interaction of the antibody with a critical receptor binding motif Arg-Gly-Asp. The conclusions of these neutralization studies are that (i) bivalent binding of antibody is not a requisite for strong neutralization of aphthoviruses and (ii) aggregation of viral particles, which has been proposed to be the dominant neutralization mechanism of antibodies that bind monovalently to virions, is not necessary for the neutralization of FMDV C-S8c1 by MAb SD6.
Insights
Monovalent antibody binding effectively neutralizes Foot-and-mouth disease virus (FMDV) by blocking attachment, without requiring viral aggregation. This challenges previous assumptions about antibody neutralization mechanisms for aphthoviruses.
Area of Science:
- Virology
- Immunology
- Structural Biology
Background:
- Aphthoviruses, like Foot-and-mouth disease virus (FMDV), are significant pathogens.
- Antibody-mediated neutralization is crucial for controlling viral infections.
- Previous models suggested viral aggregation is essential for antibody neutralization.
Purpose of the Study:
- To investigate the mechanism of FMDV neutralization by a specific monoclonal antibody (MAb SD6).
- To determine if monovalent antibody binding is sufficient for effective neutralization.
- To assess the role of viral aggregation in FMDV neutralization.
Main Methods:
- Neutralization assays using FMDV clone C-S8c1 and MAb SD6 (intact and Fab fragment).
- Virus attachment assays to cells.
- Sucrose gradient sedimentation to detect viral aggregation.
- Analysis integrated with X-ray crystallography and cryo-electron microscopy data.
Main Results:
- MAb SD6, binding monovalently to the Arg-Gly-Asp motif on VP1, effectively neutralized FMDV.
- Both intact antibody and its Fab fragment blocked virus attachment to cells.
- No significant viral aggregation was observed, even at high antibody concentrations.
- Fab fragment showed only a fivefold reduction in neutralization activity compared to the intact antibody.
Conclusions:
- Bivalent antibody binding is not essential for potent aphthovirus neutralization.
- Viral aggregation is not a prerequisite for neutralizing FMDV with MAb SD6.
- Monovalent binding and blocking viral attachment are sufficient for effective FMDV neutralization.