Author's School

Graduate School of Arts & Sciences

Author's Department/Program

Biology and Biomedical Sciences: Immunology

Language

English (en)

Date of Award

Spring 2-28-2013

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Chair and Committee

Michael S Diamond

Abstract

West Nile virus: WNV) is a neurotropic flavivirus capable of causing severe disease and death in humans. Studies in mice have demonstrated that the humoral immune response against WNV limits primary infection and protects against a secondary challenge. Accordingly, passive transfer of immune serum or monoclonal antibodies: MAb) against the envelope: E) protein either prior to WNV infection or shortly thereafter is sufficient to protect mice from disease. The E protein is an immunodominant antigen in the antibody response to WNV infection, and the most potent neutralizing MAbs recognize an epitope on the lateral ridge of domain III: DIII-LR) of the E protein. However, studies with serum from human patients show that antibodies against the DIII-LR epitope comprise at best, a minor component of the human anti-WNV antibody response. Rather, the human anti-E protein response is more dominantly directed against an epitope on the fusion loop of domain II: DII-FL), and antibodies against this epitope neutralize infection poorly in vitro. The studies described in this thesis examined how the antibody response to WNV is protective despite being skewed away from the most potently neutralizing epitope: DIII-LR). In the first section, two WNV-specific human MAbs that were isolated from B cell populations of convalescent patients that strongly neutralized WNV infection in vitro and protected mice against lethal infection in vivo were characterized in detail. The MAbs were localized to E protein epitopes that are present only on intact WNV virions and subviral particles, and neutralization of infection occurred through a viral fusion blockade mechanism, similar to DIII-LR MAbs. This suggests that WNV infection may indeed induce strongly neutralizing antibodies, which simply go undetected by current epitope-specific diagnostics that utilize recombinant, monomeric E protein. Subsequently, a DII-FL mouse MAb that was non-neutralizing in vitro was shown to protect mice from WNV infection in vivo via its Fc effector functions, requiring C1q, Fc-gamma receptor III: CD16), and phagocytic cells. This highlights the limitations of current in vitro surrogate markers of protection, which cannot account for the beneficial effects conferred by immunodominant DII-FL antibodies. Overall, these studies provide an enhanced understanding of the mechanisms of protection of the human anti-WNV antibody response.

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Permanent URL: http://dx.doi.org/10.7936/K77H1GKC

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