Mast cell tryptase activates peripheral blood eosinophils to release granule-associated enzymes.
BACKGROUND
Mast cells and eosinophils are important effector cells in asthma. Understanding their interactions is essential for studying asthma pathophysiology. Inflammatory mediators released from mast cells, such as arachidonic acid metabolites, TNF and IL-5, are important in eosinophil biology. However, little is known about the effects of mast cell-specific mediators, such as tryptase, on eosinophils. Our objective was to investigate the effects of mast cell tryptase on human peripheral blood eosinophils.


METHODS
Peripheral blood eosinophils isolated from asthmatic individuals were activated using various concentrations of tryptase- and protease-activated receptor-2 (PAR-2)-activating peptides (PAR-2 AP). Eosinophil activation was evaluated by the release of granule mediators, superoxide release, estimation of eosinophil survival, changes in intracellular Ca2+ concentration and mitogen-activated protein kinase activation.


RESULTS
Tryptase induced the release of eosinophil peroxidase and beta-hexosaminidase from peripheral blood eosinophils but had no effect on RANTES release. Eosinophils isolated from two thirds of our donors responded to tryptase, while the remainder appeared not to respond. Release of granule mediators was dependent on tryptase enzymatic activity. To identify the mechanism of eosinophil activation by tryptase, we studied the expression of PAR-2 by eosinophils and its function. Using RT-PCR, we amplified PAR-2 from eosinophils. However, flow cytometry failed to detect significant PAR-2 expression on the surface of eosinophils. The PAR-2 AP SLIGRL-NH2 did not induce eosinophil activation by any of the methods we employed.


CONCLUSIONS
Our data indicate that mast cell tryptase may affect eosinophil activation status independently of PAR-2.
Pulmonary Research Group, Department of Medicine, University of Alberta, Edmonton, Alta., Canada.
Harissios
H
Vliagoftis
Paige
P
Lacy
Betty
B
Luy
Darryl
D
Adamko
Morley
M
Hollenberg
Dean
D
Befus
Redwan
R
Moqbel
D001249:Asthma / Q000276:immunology*; D002118:Calcium / Q000276:immunology; D018946:Chemokine CCL5 / Q000097:blood / Q000276:immunology; D003594:Cytoplasmic Granules / Q000201:enzymology* / Q000276:immunology; D047209:Eosinophil Peroxidase / Q000097:blood / Q000276:immunology; D004804:Eosinophils / Q000166:cytology / Q000201:enzymology / Q000276:immunology*; D005434:Flow Cytometry; D006801:Humans; D008407:Mast Cells / Q000201:enzymology* / Q000276:immunology; D018375:Neutrophil Activation / Q000276:immunology*; D044464:Receptor, PAR-2 / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012697:Serine Endopeptidases / Q000276:immunology*; D053802:Tryptases; D001619:beta-N-Acetylhexosaminidases / Q000097:blood / Q000276:immunology
D018946:Chemokine CCL5; D044464:Receptor, PAR-2; D047209:Eosinophil Peroxidase; D001619:beta-N-Acetylhexosaminidases; D012697:Serine Endopeptidases; D053802:Tryptases; D002118:Calcium