Defense Date

2007

Document Type

Dissertation

Degree Name

Doctor of Philosophy

Department

Microbiology & Immunology

First Advisor

Dr. Daniel H. Conrad

Abstract

Through underexpression and overexpression studies, CD23 has been shown to negatively regulate IgE production. To investigate CD23 destabilization and its effects on CD23 shedding and IgE synthesis in vivo, we utilized an anti-CD23 stalk monoclonal (19G5) which has previously been shown to enhance proteolysis of CD23 in vitro. Compared to isotype control-treated mice, mice injected with 19G5 displayed enhanced serum soluble CD23 and IgE. Because 19G5 injection substantially enhanced CD23 shedding, it was useful in investigating the identity of the CD23 sheddase. 19G5 enhanced CD23 shedding in ADAM8-/-, ADAM9-/-ADAM15-/-, and ADAM9-/-ADAM12-/-ADAM15-/- mice, ruling out these ADAMs as candidate CD23 sheddases. Through the use of an ADAM10 inhibitor, we blocked CD23 shedding from murine B cells while increasing CD23 surface levels, and thus we identified ADAM10 as the CD23 sheddase. During the course of the ADAM investigation, we discovered that the 129/SvJ inbred mouse strain carried five amino acid substitutions within its CD23 gene. The mutations resulted in reduced CD23 surface expression and hyper IgE levels in vivo. The hyper IgE phenotype was consistent with a more rapid clearance of Nippostrongylus brasiliensis from the gut of 129/SvJ mice. B cells from 129/SvJ spleens proliferated more rapidly than those from BALB/c after stimulation with IL-4 and CD40 ligand trimer in vitro. However, in vitro IgE levels in supernatants from 129/SvJ B cells were significantly reduced, suggesting that the B cells were no longer responsive to IL-4 in vitro. Although the affinity of the IgE-129/SvJ CD23 interaction was similar to that of the BALB/c, 129/SvJ B cells exhibited a reduced number of IgE binding sites, demonstrating that high levels of CD23 are essential for controlling IgE synthesis. This finding was further confirmed in another disease model, namely the mouse asthma model. Mice overexpressing CD23 displayed suppressed allergic lung inflammation and reduced levels of IgE and Th2 cytokines and chemokines. Overall, the data provide a direct demonstration for CD23's role in regulating IgE production in vivo and suggest that therapies aimed at stabilizing cell surface CD23 would inhibit proteolysis and increase surface expression, and thus would be beneficial in controlling allergic disease.

Rights

© The Author

Is Part Of

VCU University Archives

Is Part Of

VCU Theses and Dissertations

Date of Submission

June 2008

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