Characterisation of CD23 cleavage by endogenous and exogenous proteases using neo-epitope antibodies

CD23 is the low affinity IgE receptor. It is a type II integral transmembrane glycoprotein that can be shed from the cell surface forming soluble products of approximately 37, 33, 29, 25 and 16kDa.;It appears that membrane and soluble CD23 have opposing regulatory functions and that inhibition of CD23 shedding may have potential to alleviate both allergic and inflammatory diseases. This has focused attention on the endogenous protease(s) responsible for CD23 shedding, leading to the demonstration that both the 37 and 33kDA sCD23 fragments are cleaved from the cell surface by a metalloprotease.;In order to characterise the cleavage events within CD23, anti-neoepitope antibodies specific for the newly created amino and carboxy termini of the two predominant cleavage sties within CD23 (producing the 37 and 25kDa soluble CD23 products) were raised. Characterisation of these antibodies demonstrated that the proteolytic cleavage events responsible for creating the 37 and 25kDa sCD23 fragments are independent of each other. Furthermore, two different proteases were shown to be responsible for cleaving these two fragments. The work described in this thesis confirms previous reports that 37kDA sCD23 is cleaved by a metalloprotease, however cleavage of the 25kDa fragment was not inhibited by metalloprotease inhibitors.;The production of the two different sized sCD23 molecules by different proteases has important implications for targeting the proteolytic cleavage events to alleviate symptoms of allergic and inflammatory diseases. This emphasises the importance of defining the biological functions of mCD23 and each of the sCD23 molecules.