Eosinophil leukocyte degranulation in response to serum-opsonized beads: C5a and platelet-activating factor enhance ECP release, with roles for protein kinases A and C.
BACKGROUND
Eosinophils have a typical content of granule-bound, cytotoxic, cationic proteins which may, when released to the external milieu, play roles in diseases such as asthma and parasitic infestation. Therefore, we have investigated possible mechanisms by which their release is regulated in eosinophils.


METHODS
The enzyme-linked immunosorbent assay (ELISA) was used to detect released eosinophil cationic protein (ECP). Release of ECP was induced by serum-opsonized, nonphagocytosable Sephadex beads (SOS).


RESULTS
The complement fragment C5a and platelet-activating factor (PAF) were found to enhance ECP release in response to SOS in a dose-dependent fashion, and, contrary to previous reports, they were not found to act as secretagogues themselves on eosinophils in suspension. The role of protein kinase C (PKC) in eosinophil degranulation has been controversial. We found that ECP release induced by SOS was inhibited by the PKC inhibitors staurosporine and calphostin C. Activation of protein kinase A (PKA), by raising cAMP, also inhibited ECP release. Furthermore, pertussis toxin decreased ECP release on opsonized beads, indicating the involvement of pertussis-toxin-sensitive G proteins.


CONCLUSIONS
C5a, and PAF enhance granule release, rather than acting as secretagogues themselves. PKC and PKA have opposing roles in the regulation of ECP release in response to SOS.
Egesten
A
A
Department of Medicine, Lund University, University Hospital MAS, Malmö, Sweden.
Malm
J
J
D001798:Blood Proteins / Q000032:analysis / Q000037:antagonists & inhibitors / Q000187:drug effects*; D015550:Cell Degranulation / Q000187:drug effects* / Q000502:physiology; D015936:Complement C5a / Q000494:pharmacology*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors / Q000502:physiology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004797:Enzyme-Linked Immunosorbent Assay; D047091:Eosinophil Granule Proteins; D004804:Eosinophils / Q000187:drug effects* / Q000502:physiology; D006801:Humans; D009281:Naphthalenes / Q000494:pharmacology; D010972:Platelet Activating Factor / Q000494:pharmacology*; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000502:physiology; D012260:Ribonucleases; D019311:Staurosporine / Q000494:pharmacology; D013997:Time Factors
D001798:Blood Proteins; D004791:Enzyme Inhibitors; D047091:Eosinophil Granule Proteins; D009281:Naphthalenes; D010972:Platelet Activating Factor; D015936:Complement C5a; D017868:Cyclic AMP-Dependent Protein Kinases; D011493:Protein Kinase C; D012260:Ribonucleases; D019311:Staurosporine; C058819:calphostin C