Defense Date

2010

Document Type

Dissertation

Degree Name

Doctor of Philosophy

Department

Microbiology & Immunology

First Advisor

Daniel Conrad

Abstract

CD23 has long been appreciated to be a natural, negative regulator of IgE synthesis. This understanding is due in part to animal models in which CD23 deficient or CD23 transgenic animals display exacerbated or reduced IgE levels respectively. Interestingly, CD23 is susceptible to proteolytic cleavage from the cell surface. When this occurs, CD23 loses its regulatory capability and the solubilized form can lead to pro-inflammatory events through its cytokinergic activity on macrophages. Thus, targeting this specific cleavage would be beneficial to the control of allergic disease by stabilizing CD23 at the cell surface. Inhibitor studies performed by our group as well as others indicate that the enzyme responsible for CD23 ectodomain shedding is a hydroxamate-sensitive metalloproteinase. Through collaboration with the Blobel group, we analyzed various ADAM KO mouse embryonic fibroblasts (MEFs) and found no involvement of ADAMs 8,9,12,15,17,19, and 33 in CD23 shedding, however we did find a role for ADAM10. Using ADAM10 KO MEFs and ADAM10 specific inhibitors, we discovered that ADAM10 is indeed the CD23 cleaving enzyme or “sheddase”. Thus, developing strategies that would target ADAM10 could have an effect on sCD23 release and IgE production. In the CNS, signaling through the kainate receptor (KAR) by glutamate causes an increase in ADAM10 expression. Human B cells were found to express a GluK2 containing kainate receptor and its activation increased ADAM10 expression which is in agreement with KAR activation in the CNS. Although glutamate is considered a neurotransmitter, it signals in the periphery and elevated levels are associated with certain immune disorders. A significant corresponding increase in sCD23 release is observed as well. Remarkably, this activation induced a strong increase in B cell proliferation, IgG, and IgE production and these events can be reversed through the use of NS102, a specific KAR antagonist. Thus, we report for the first time the unique presence on B cells of a neurotransmitter receptor and that activation of this receptor could serve as a novel mechanism for enhancing B cell activation and Ig production. This enhancement and control thereof has implications for allergic and autoimmune diseases. Lastly, the CD23-ADAM10 axis was examined in a non-allergic disease state, B cell chronic lymphocytic leukemia (BCLL). BCLL is characterized by a large accumulation of CD23+ cells and high levels of soluble CD23 in the sera. After further analysis, we show that ADAM10 is indeed over-expressed in BCLL and could account for the high levels seen in this patient population. Furthermore, specifically targeting ADAM10 resulted in reduced soluble CD23 release, reduced proliferation, and enhanced apoptosis induction. Taken together the novel finding that ADAM10 is involved in CD23 shedding allows for targeted therapeutic intervention of both atopic and non-atopic disease states.

Rights

© The Author

Is Part Of

VCU University Archives

Is Part Of

VCU Theses and Dissertations

Date of Submission

September 2010

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