T-helper 2 cytokines attenuate senescent eosinophil activation by the CXCR4 ligand stromal-derived factor-1alpha (CXCL12).

Background: Different chemokine receptors have been suggested to play a pivotal role in allergic diseases and therefore to be relevant for the activation of effector cells and propagation of the inflammatory response. The CXC chemokine receptor CXCR4 has recently been found on the surface of eosinophils implicating a role in allergic diseases.

Objective: The aim of this study was to investigate the functional expression of CXCR4 on senescent eosinophils. Moreover, we questioned whether the cytokine profile--T-helper (Th)1 and Th2 cytokines--affect the activation of eosinophils via the CXCR4 that could be important for the different phases of the allergic reaction.

Methods: CXCR4 expression on human eosinophils was analysed by flow cytometry and RT-PCR. Functional analyses of intracellular calcium fluxes, actin polymerization, release of reactive oxygen species and, chemotaxis were carried out using spectrofluorometry, flow cytometry, chemiluminescence and modified Boyden chamber technique.

Results: Whole blood and freshly isolated eosinophils weakly express CXCR4 surface protein. Incubation in culture medium without addition of cytokines for 24 h always lead to strong CXCR4 surface expression that paralleled with stromal-derived factor-1alpha (CXCL12)-induced eosinophil activation. Stimulation of eosinophils with CXCL12 leads to an internalization of CXCR4, which could be prevented by phenylarsine oxide. Co-incubation of eosinophils with Th2 cytokines such as IL-3, IL-4, IL-5, IL-13, and granulocyte macrophage-colony stimulating factor prevented the expression of CXCR4 and affected eosinophil activation after stimulation with the CXCR4 ligand CXCL12. From these cytokines, IL-3 was the only cytokine completely inhibited intracellular calcium fluxes and chemotaxis of eosinophils in response to CXCL12.

Conclusion: Senescent eosinophils express functional CXCR4 receptors, which are prevented by Th2 cytokines that are found in the early phase of allergic reaction. Therefore, CXCR4 activation of eosinophils seems to be important in the chronic phase of allergic reaction, which is dominated by a Th1 cytokine profile.