Studies of Eosinophil Cationic Protein (ECP) in vivo and in vitro : Impact of Genetic and Posttranslational Modifications

Sammanfattning: Eosinophil granulocytes are tissue dwelling leukocytes that are implicated in host defence, particularly against helminthic parasites; they also participate in most inflammatory disorders. Although eosinophils have important roles in host defence mechanisms, their actions can also be harmful to the host as in the allergic inflammation where lung epithelium is destructed due to the release of toxic granule proteins. The focus of the present thesis work has been to characterize the molecular and functional heterogeneity of the granule protein Eosinophil Cationic Protein (ECP). We investigated a coding ECP gene polymorphism (arg97thr) in an African population endemically exposed to the Schistosoma mansoni parasite and found a correlation between ECP genotype and disease manifestations; ECP97arg was more effective in terms of host defence against the parasite, but was also correlated to development of liver fibrosis in infected subjects. We purified ECP97arg and ECP97thr from healthy blood donors and showed that they differ in their cytotoxic activities; ECP97arg was cytotoxic whereas ECP97thr was non-cytotoxic. They did not differ in terms of RNase activity or in their ability to stimulate fibroblast-mediated collagen gel contraction. We developed a new SELDI-TOF MS assay to enable the study of the structure of ECP in more detail and showed that ECP is produced in several glycosylated forms, and that the degree of glycosylation determines the cytotoxic activity. Enzymatic deglycosylation significantly enhanced the cytotoxic activity of highly glycosylated ECP-variants.To summarize, in this thesis we demonstrated that the cytotoxic activity of ECP is dependent on both a gene polymorphism and post-translational modifications, and that the cytotoxic activity is distinct from other functions of ECP. We speculate that ECP is synthesised in heavily glycosylated variants as a means to protect the host from its harmful effects and that ECP is activated by deglycosylation when required at the site of inflammation.