Synergic production of neutrophil chemotactic activity by colonic epithelial cells and eosinophils.

The presence of eosinophils in the lumen and mucosa of the intestine is characteristic of both ulcerative colitis (UC) and Crohn's disease (CD). There is evidence of eosinophil activation in the intestine during acute inflammatory episodes of these diseases; these episodes are also characterized by an influx of neutrophils, which have the potential to cause extensive tissue damage. We undertook a study to determine whether eosinophils in contact with colonic epithelial cells produce factors that may attract neutrophils in response to immunological stimulation. Neutrophil chemotactic activity (NCA) and concentrations of three neutrophil-attracting CXC chemokines - CXCL1 (Groα), CXCL5 (Ena78) and CXCL8 (IL8) - were measured in supernatants of T84 colonic epithelial cells and blood eosinophils or eosinophil-like myeloid leukaemia cells (AML14.3D10), alone or in combination. Cells were stimulated with serum-opsonized zymosan (OZ) particles. NCA (P<0.005) and CXCL5 levels (P<0.05) in the supernatants of OZ-stimulated epithelial/eosinophil co-cultures were significantly higher than in the supernatants of either cell type alone. Release of CXCL1 (P<0.05) and CXCL8 (P<0.01) from OZ-stimulated co-culture supernatants was significantly higher than from OZ-stimulated eosinophils but not higher than from OZ-stimulated epithelial cells. Eosinophils and colonic epithelial cells exhibit synergy in production of neutrophil chemoattractants in response to immunological stimulation. This may represent a mechanism for exaggerated recruitment of neutrophils to the intestine in response to acute infection in conditions that are characterized by the presence of eosinophils in the bowel.

Phosphoinositide 3-kinase gamma mediates chemotactic responses of human eosinophils to platelet-activating factor.

BACKGROUND: Eosinophils are characteristic participants in allergic inflammation. The intracellular signalling mechanisms involved in the migration of eosinophils to sites of allergic inflammation are poorly understood. Chemotactic responses of eosinophils to platelet-activating factor (PAF), but not eotaxin, have been demonstrated to be dependent upon the activation of phosphoinositide 3-kinase (PI3K) but the specific isoform of PI3K involved has not been identified. OBJECTIVE: To determine the roles of the leukocyte-specific PI3K gamma and PI3K delta isoforms of PI3K in PAF-induced chemotaxis of human eosinophils. METHODS: Chemotactic responses of the EoL-1 eosinophilic cell line and human peripheral blood eosinophils were measured. The effects of a PI3K gamma-selective inhibitor (5-[2,2-difluorobenzo(1,3)dioxol-5-ylmethylene]-thiazolidine-2,4-dione; AS604850) and gene knock-down of PI3K gamma and PI3K delta on chemotactic responses were determined. RESULTS: AS604850 caused a concentration-dependent suppression of chemotactic responses of EoL-1 cells and blood eosinophils to PAF but not eotaxin. Specific siRNAs reduced the expression of PI3K gamma and PI3K delta in EoL-1 cells. Knock-down of PI3K gamma by siRNA resulted in a 75% inhibition of the chemotactic response to PAF but had no effect on the response to eotaxin. Knock-down of endogenous PI3K delta by siRNA resulted in a 38% inhibition of the chemotactic response to PAF but had no effect on the response to eotaxin. CONCLUSION: PI3K gamma plays a major role in the induction of chemotaxis in PAF-stimulated eosinophils, while PI3K delta plays a lesser role. Interventions which reduce the activity of PI3K gamma may have therapeutic potential in allergic diseases.