Analysis of Signal Transduction Pathways in Human Eosinophils Activated by Chemoattractants and the T-Helper 2–Derived Cytokines Interleukin-4 and Interleukin-5

Abstract

Activation and recruitment of eosinophils in allergic inflammation is in part mediated by chemoattractants and T-helper 2 (Th2)-derived cytokines. However, little is known concerning the signal transduction mechanisms by which this activation occurs. We have investigated tyrosine kinase-mediated activation of phosphatidylinositol 3-kinase (PI3K) and compared this with the activation of the p21ras-ERK signaling pathway in human eosinophils. The related cytokines interleukin-3 (IL-3), IL-5, and granulocyte-macrophage colony-stimulating factor (GM-CSF), all induced PI3K activity detected in antiphosphotyrosine immunoprecipitates. Furthermore, the chemoattractants platelet-activating factor (PAF), RANTES, and C5a were also able to induce phosphotyrosine-associated PI3K activity. Protein kinase B (PKB) is a downstream target of PI3K activation by growth factors. Induction of PKB phosphorylation in human eosinophils was transiently induced on activation with the cytokines IL-4 and IL-5, as well as the chemoattractants PAF, C5a, and RANTES showing a broad activation profile. Surprisingly, analysis of the activation of the mitogen-activated protein (MAP) kinases p44ERK1 and p42ERK2, showed that ERK2, but not ERK1, was transiently activated in human eosinophils after stimulation with IL-5 or PAF. Activation kinetics correlated with activation of p21ras by both cytokines and chemoattractants as measured by a novel assay for guanosine triphosphate (GTP)-loading. Finally, using specific inhibitors of both the p21ras-ERK and PI3K signaling pathways, a role was demonstrated for PI3K, but not p21ras-ERK, in activation of the serum-treated zymosan (STZ)-mediated respiratory burst in IL-5 and PAF-primed eosinophils. In summary, these data show that in human eosinophils, Th2-derived cytokines differentially activate both PI3K and MAP kinase signal transduction pathways with distinct functional consequences showing complex regulation of eosinophil effector functions.

The relationship between persistent secretion of RANTES and residual infiltration of eosinophils and memory T lymphocytes afterHelicobacter pylori eradication

“…Eosinophils also express various membrane receptors for immunoglobulins, complement, cytokines, and adhesion molecules, as well as CD4 and class II MHC (major histocompatibility complex), and can function as antigen‐presenting cells33. In addition, their activation is closely related to the T‐helper 2 cytokine profile such as IL‐534 and they can then also release various cytokines and growth factors, including their own differentiation factors33. These findings have allowed a re‐evaluation of the role of eosinophils in immune response; in particular, these functions of eosinophils seem beneficial for the defence mechanism linked with memory T lymphocytes in HP‐eradicated gastric mucosa.…”

Protein Translation and Signaling in Human Eosinophils

“…Mitogen-activated protein kinases have important roles in many critical events, including EOS survival, migration, adhesion, production of inflammatory mediators, and degranulation. In EOS, ERK and p38 are phosphorylated and active following stimulation with a variety of mediators, including the β-chain cytokines (IL-3, IL-5, and GM-CSF), chemokines, fMLP, the PAF, and matrix proteins ( 26 , 28 , 53 , 57 , 64 – 71 ). Table 3 shows the expression levels of ERK, and their downstream targets, RSK1–3 (p90S6K), all of which are phosphorylated at a detectable level in resting cells.…”

Interleukin-15 Inhibits Spontaneous Apoptosis in Human Eosinophils via Autocrine Production of Granulocyte Macrophage–Colony Stimulating Factor and Nuclear Factor- κ B Activation

“…The classic hematopoietins, interleukin (IL)-3, IL-5, and granulocyte macrophage-colony stimulating factor (GM-CSF), constitute a cytokine family well known to inhibit apoptosis in these cells (4)(5)(6). The signaling pathways for IL-5 and GM-CSF have been partially delineated and found to be dependent on phosphorylation of Lyn and Syk and activation of p21 Ras/Raf-1, Jak -2/Stat, and PI3 kinase pathways (7,8). Although IL-5, produced by T cells and to a lesser extent eosinophils, is the most specific cytokine for eosinophils, GM-CSF is widely expressed by human myofibroblasts, endothelial cells, airway epithelial cells, and eosinophils themselves, suggesting a potentially important role as both an autocrine and paracrine factor (4,(9)(10)(11).…”