Raman imaging highlights biochemical heterogeneity of human eosinophils versus human eosinophilic leukaemia cell line.

Eosinophils are acidophilic granulocytes that develop in the bone marrow. Although their population contributes only to approximately 1-6% of all leucocytes present in the human blood, they possess a wide range of specific functions. They play a key role in inflammation-regulating processes, when their numbers can increased to above 5 × 109 /l of peripheral blood. Their characteristic feature is the presence of granules containing eosinophil peroxidase (EPO), the release of which can trigger a cascade of events promoting oxidative stress, apoptosis or necrosis, leading finally to cell death. Raman spectroscopy is a powerful technique to detect EPO, which comprises a chromophore protoporphyrin IX. Another cell structure associated with inflammation processes are lipid bodies (lipid-rich organelles), also well recognized and imaged using high resolution confocal Raman spectroscopy. In this work, eosinophils isolated from the blood of a human donor were analysed versus their model, EoL-1 human eosinophilic leukaemia cell line, by Raman spectroscopic imaging. We showed that EPO was present only in primary cells and not found in the cell line. Eosinophils were activated using phorbol 12-myristate 13-acetate, which resulted in lipid bodies formation. An effect of cells stimulation was studied and compared for eosinophils and EoL-1.