Eosinophil Cationic Protein : Expression Levels and Polymorphisms

Abstract: The eosinophil cationic protein (ECP) is usually associated with the eosinophil granulocyte. In this thesis the presence and production of this protein has been studied in two other cells. The circulating monocyte was found to contain ECP mRNA and small amounts of ECP, one thousand times less than that found in the eosinophil. The production decreased by differentiation of the myelomonoblastic cell line U937 into a macrophage phenotype. Submucosal lung macrophages did not stain for ECP and alveolar macrophages did not contain ECP mRNA. The circulating neutrophil contains ECP at a level hundred fold less than the eosinophil. We found that the protein is located to the primary granules of the neutrophil but could detect no ECP mRNA in the cell. It was shown in vitro that the protein was taken up by the cell and partly transported to the primary granules. The uptake did not seem to be receptor mediated. Upon stimulation of the neutrophils, ECP previously taken up, was re-secreted. The ECP protein is heterogeneous both to molecular characteristics and to function. To evaluate if a genetic component is involved, the ECP gene was analysed in 70 individuals. Three single nucleotide polymorphisms (SNP´s) were found, denoted 277(C>T), 434(G>C) and 562(G>C). The two first were located to the mature peptide-coding region and would change the amino acids, arg45cys and arg97thr. The prevalence of the most common SNP, 434, was evaluated in two eosinophil-related diseases, allergy/asthma and Hodgkin Lymphoma (HL). Forty-three HL patients were evaluated and it was found that the 434GG was significantly more prevalent in patients having nodular sclerosis (NS) as compared to other histologies (p=0.03). Erythrocyte sedimentation rate was also related to the 434GG genotype (p=0.009). In 209 medical students 434GG was more common (p=0.002) in those who indicated allergy. The genotype was unrelated to the production of IgE antibodies to allergens. In analysis of 76 subjects with asthma it was found that the 434GG genotype was significantly more common among allergic asthmatics (p=0.04). Asthma and HL-NS are characterized by fibrosis and eosinophils and ECP has been suggested in fibrosis development.