Activation of the respiratory burst in human eosinophils by chemotaxins requires intracellular calcium fluxes.
Eosinophils represent major effector cells in the allergic inflammatory response. Following activation, these cells are capable of mediating tissue damage, particularly by the release of reactive oxygen species. In this study, the role of extracellular and intracellular calcium in the induction of the respiratory burst of human eosinophils was investigated in healthy non-atopic individuals. Pre-incubation of Fura-2-loaded eosinophils with the intracellular calcium chelator 2-bis(o-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid prevented the increase of the [Ca++]i following stimulation by RANTES, C5a and PAF, in concentration-dependent fashion, whereas depletion of extracellular calcium in the test medium by ethyl=eneglycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid was ineffective. To investigate the potential role of extracellular and intracellular calcium on the production of reactive oxygen species, flow-cytometric measurement of H2O2 production by dihydrorhodamine 123 and lucigenin-dependent chemiluminescence were carried out. Chelation of both intracellular and extracellular calcium prevented production of reactive oxygen species after stimulation with C5a, PAF, or RANTES. However, production of reactive oxygen species after stimulation by phorbol myristate acetate, which bypasses post-receptor events by direct activation of protein kinase C, was prevented only after chelation of intracellular but not extracellular calcium. This suggested a Ca(++)-sensitive form of protein kinase C in the activation process of the respiratory burst. These data demonstrate that intracellular and extracellular calcium represent a prerequisite of chemotaxin-induced activation of the respiratory burst in human eosinophils. Thus, intracellular calcium seems to play a central role in the modulation of the respiratory burst in eosinophils and might therefore be an interesting target for drugs that interfere with calcium homeostasis and reduce the tissue destructive power of eosinophils.
Elsner
J
J
Department of Dermatology, Hannover Medical School, Germany.
Dichmann
S
S
Kapp
A
A
D002118:Calcium / Q000378:metabolism*; D002614:Chelating Agents / Q000494:pharmacology; D002630:Chemotactic Factors / Q000494:pharmacology*; D004492:Edetic Acid / Q000494:pharmacology; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D004804:Eosinophils / Q000378:metabolism*; D005110:Extracellular Space / Q000378:metabolism; D006801:Humans; D006861:Hydrogen Peroxide / Q000378:metabolism; D007425:Intracellular Membranes / Q000378:metabolism*; D017382:Reactive Oxygen Species / Q000378:metabolism; D016897:Respiratory Burst
D002614:Chelating Agents; D002630:Chemotactic Factors; D017382:Reactive Oxygen Species; C070379:1,2-bis(2-aminophenoxy)ethane N,N,N',N'-tetraacetic acid acetoxymethyl ester; D004533:Egtazic Acid; D004492:Edetic Acid; D006861:Hydrogen Peroxide; D002118:Calcium