Signal transduction in activation of human eosinophils: G protein-dependent and -independent pathways

C3b-induced eosinophil degranulation involves PI3-kinases and is inhibited by protein kinase C activity

Selective release of individual eosinophil granule proteins has been demonstrated in eosinophilic conditions and in vitro using different stimuli. The aim of this study was to investigate if selective release of eosinophil cationic protein (ECP), eosinophil protein X/eosinophil derived-neurotoxin (EPX/EDN) and eosinophil peroxidase (EPO) could be due to the involvement of different signal transduction pathways. Peripheral blood granulocytes from healthy donors were incubated with Wortmannin, LY294002, Genistein, Staurosporine, GÖ6976 or PD98059 prior to the induction of degranulation by C3b. The released amounts of ECP, EPO and EPX/EDN were determined by immunoassays, and related to the total cell content of respective protein. Wortmannin caused a significant, dose-dependent inhibition of all three granule proteins. LY294002 (10⁻⁶ M) also inhibited the release of all proteins. Genistein (10⁻⁶ M) inhibited the release of ECP, whereas the release of EPO was increased. However, there was a tendency towards similar concentration-dependent patterns of release of all three proteins. Staurosporine (10⁻⁷ M), GÖ6976 (10⁻⁶ M) and PD98059 (10⁻⁵ M) caused an increased release of the three proteins. PI3-kinases play an important role in the C3b-induced release of ECP, EPO and EPX/EDN, whereas protein kinase C seems to have inhibitory effects on C3b-induced degranulation.

Translocation of the tetraspanin CD63 in association with human eosinophil mediator release

The tetraspanin CD63 (also known as LAMP-3) has been implicated in phagocytic and intracellular lysosome-phagosome fusion events. It is also present in eosinophils, with predominant expression on crystalloid granule membrane. However, its role in eosinophil function is obscure. We hypothesized that CD63 is associated with intracellular events involved in eosinophil activation and mediator release. We used a combination of confocal immunofluorescence microscopy, flow cytometry, and secretion assays, including beta-hexosaminidase, eosinophil peroxidase, and RANTES, to examine CD63 expression, intracellular localization, and its association with cell activation and mediator release. In resting eosinophils, CD63 immunoreactivity was localized to plasma and crystalloid granule membranes. In interferon-gamma (IFN-gamma)- or C5a/CB-stimulated cells (10 minutes), intracellular CD63 appeared to shift to the cell periphery and plasma membrane, while stimulation with a cocktail of interleukin-3 (IL-3)/IL-5/granulocyte-macrophage colony-stimulating factor induced the appearance of discrete intracellular clusters of CD63 immunoreactivity. IFN-gamma induced mobilization of CD63 to the cell periphery, which coincided with selective mobilization of RANTES prior to its release, implying CD63 association with piecemeal degranulation. Agonist-induced CD63 mobilization and cell surface up-regulation was associated with beta-hexosaminidase, eosinophil peroxidase, and RANTES release. Dexamethasone as well as genistein (a broad-spectrum inhibitor of tyrosine kinases) inhibited agonist-induced intracellular mobilization of CD63 and RANTES together with cell surface up-regulation of CD63 and mediator release. This is the first report of an association between CD63 mobilization and agonist-induced selective mediator release, which may imply the involvement of CD63 in eosinophil activation and piecemeal degranulation.

Differential activation of signal transduction pathways mediating phagocytosis, oxidative burst, and degranulation by chicken heterophils in response to stimulation with opsonized Salmonella enteritidis

The activation of signal transduction pathways is required for the expression of functional enhancement of cellular activities. In the present studies, initial attempts were made to identify the signal transduction factors involved in activating phagocytosis, generation of an oxidative burst, and degranulation by heterophils isolated from neonatal chickens in response to opsonized Salmonella enteritidis (opsonized SE). Peripheral blood heterophils were isolated and exposed to known inhibitors of signal transduction pathways for either 20 min (staurosporin, genistein, or verapamil) or 120 min (pertussis toxin) at 39 degrees C. The cells were then stimulated for 30 min at 39 degrees C with opsonized SE. Phagocytosis, luminol-dependent chemoluminescence (LDCL), and beta-D glucuronidase release were then evaluated in vitro. The G-protein inhibitor pertussin toxin markedly inhibited (>80%) phagocytosis of opsonized SE. Both the protein kinase inhibitor (staurosporin) and calcium channel inhibitor (verapamil) reduced phagocytosis in a dose response manner. Genistein, a tyrosine kinase inhibitor, had no effect on phagocytosis. Staurosporin had a marked inhibitory effect on LDCL (>90%) while genistein had a dose responsive inhibition on LDCL. Both verapamil (40-45%) and pertussin toxin (50-55%) had a statistically significant, but less biologically significant effect on LDCL. Genistein significantly reduced the degranulation (78-81%) of heterophils by opsonized SE. Staurosporin also reduced degranulation by 43-50%, but neither verapamil nor pertussis toxin had a significant effect on degranulation. These findings demonstrate that distinct signal transduction pathways differentially regulate the stimulation of the functional activities of avian heterophils. Pertussin toxin-sensitive, Ca++-dependent G-proteins appear to regulate phagocytosis of opsonized SE, protein kinase C-dependent, tyrosine kinase-dependent protein phosphorylation plays a major role in LDCL, and tyrosine kinase(s)-dependent phosphorylation regulates primary granule release.

Interleukin-5 and the regulation of eosinophil production

Eosinophils play important roles in adaptive immune responses, inflammatory processes, and disease states. Recently, considerable research has been devoted to better defining the normal and abnormal biology of these cells, specifically their origin and mechanisms of stimulation, chemotaxis, regulation, and activation. Interleukin-5 has been identified as a major regulator of eosinophil development and function. This review highlights current literature on interleukin-5 and eosinophil production. Areas covered include molecular signaling, physiologic sources of interleukin-5, and interactions between interleukin-5, eosinophils, and the bone marrow microenvironment. Clinical correlates are also presented.