Mechanisms of granule protein mobiliation in blood eosinophils
Abstract: Serum levels of eosinophil granule proteins namely ECP, EPO and EPX, which are stored in the matrix of specific granules, were shown to correlate with the course of disease in disorders involving eosinophils. The concentration of eosinophil proteins in serum is the result of their release in vivo and ex vivo during the sampling procedure. Generally, eosinophils release the content of their specific granules in three ways: exocytosis, piecemeal degranulation (PM) or cytolysis. Which of them is operating in circulating eosinophils has not yet been defined. The aim of this thesis was to study the mechanisms of granule protein release from blood eosinophils in respect of protein subcellular localization and cell ultrastructure.In patients with bacterial infections, serum levels of ECP but not EPO increased, while in patients with viral infections both proteins remained within the range of healthy controls. G-CSF is a cytokine involved in the response mechanism to bacterial but not viral infections. Administration of G-CSF to healthy subjects induced an elevation of eosinophil numbers and a preferential increase of serum EPX and ECP in comparison to EPO.The model of PM consists of the stepwise transportation of specific granule contents from the granules towards the plasma membrane. We observed that administration of G-CSF to healthy subjects and the allergen exposure of allergic subjects during the pollen season, caused changes in the ultrastructure of eosinophil specific granules such as loosening of the matrix, granule matrix lucency and ragged losses of their core. Similar alterations of morphology had been previously described for eosinophils undergoing PM.ECP, EPX and EPO were localized not only in the specific granules but also in extra-granular compartments as shown both by immuno electron microscopy and subcelular fractionations, An extra-granular EPX compartment was present in healthy as well as in allergic and in hypereosinophilic subjects, and there were no significant differences in its size between the groups. The size of the extra-granular compartments of ECP and EPO was increased in allergics during the season, and these compartments were clearly separate from that of EPX. Results of this show the differential mobilization ofgranule proteins in blood stream eosinophils serum and indicates PM as its mechanism.
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