Protective Antiviral Antibodies that Lack Neutralizing Activity: Precedents and Evolution of Concepts
Alan L. Schmaljohn
Affiliation: Department of Microbiology and Immunology, University of Maryland School of Medicine, Baltimore, MD, USA.
Keywords: ADCC, antibody, non-neutralizing antibodies, passive immunity, virus.
Antibody-mediated resistance to viral disease is often attributed solely to neutralizing antibodies (NAbs)
despite a body of evidence -- more than 30 years in the making -- to show that other populations of antibodies (protective
non-neutralizing antibodies, PnNAbs) can also contribute and are sometimes pivotal in host resistance to viruses.
Recently, interest in varieties of PnNAbs has been restored and elevated by an HIV vaccine trial in which virus-specific
nNAbs have been highlighted as a positive correlate of immunity. Here, I briefly review some of the historical precedents
with many viruses other than HIV, along with the emergence of data over the course of some four decades, pointing
emphatically to the importance of subsets of antiviral antibodies that operate by mechanisms other than classical virus
neutralization. Foremost among suspected mechanisms of protection by PnNAbs is antibody-dependent cellular
cytotoxicty (ADCC), but additional mechanisms have sometimes been incriminated or not experimentally excluded.
Examples are given for the diversity of proteins and cognate epitopes bound by PnNAbs. Some such epitopes are
restricted to virus-infected cell surfaces or found on secreted proteins; others may be associated with virions but
unavailable to antibodies during much of the viral cycle; these are epitopes variously described as cryptic, transitional,
dynamic, or reversibly masked.
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