Release of granule proteins from human eosinophils stimulated with mast-cell mediators

It has been suggested that mast cells and eosinophils are major effector cells in the pathogenesis of allergic diseases. However, the interaction of these cells has not been thoroughly elucidated. We examined eosinophil cationic protein (ECP) release and cytosolic free calcium concentration ([Ca2+]i) in human eosinophils induced by the major mast-cell mediators including cytokines.

Eosinophils from healthy donors were stimulated with the major mast-cell mediators for 20 min after preincubation with cytochalasin B for 10 min. ECP in supernatants was measured by radioimmunoassay. Moreover, to examine changes of [Ca2+]i in eosinophils, Fura-2-loaded eosinophils were monitored for fluorescence changes after stimulus addition.

Of the tested mediators (prostaglandin [PG]D2, leukotriene (LT)B4, platelet-activating factor (PAF), histamine, LTC4, and eosinophil chemotactic factor of anaphylaxis [ECF-A]), LTB4 and PAF induced ECP release from eosinophils. Any cytokines produced by human mast cells, i.e., interleukin (IL)-4, IL-5, IL-8, tumor necrosis factor (TNF), or granulocyte-macrophage colony-stimulating factor (GM-CSF), did not induce ECP release in our system. ECP release triggered with LTB4 and PAF occurred at concentrations of 10(-8)-10(-6) M concentration-dependently. LTB4 and PAF also elicited a rise in [Ca2+]i in eosinophils. Neither PGD2, histamine, nor LTC4 induced ECP release, although they increased cytosolic calcium in eosinophils.

Of mast-cell mediators, LTB4 and PAF induced eosinophil degranulation. The contribution of LTB4 and PAF from mast cells to eosinophil degranulation may be important in the pathogenesis of allergic inflammatory diseases.