Regulation of chemokine receptor expression in eosinophils

Signals via chemokine receptors play an important role in the accumulation of eosinophils at allergic inflammatory sites. Eosinophils constitutively express CC chemokine receptor 3 (CCR3) and, to a lesser extent, CCR1. CCR3 is mainly responsible for migration of resting eosinophils, and its specific ligand, eotaxin, represents the most potent chemoattractant for eosinophils. Some reports also suggest the expression of CXC chemokine receptor 1 (CXCR1) and/or CXCR2 in eosinophils. In addition, we recently reported the functional expression of CXCR4. The ligand of CXCR4, stromal cell-derived factor-1 (SDF-1), was able to induce a strong migratory response comparable to that by eotaxin. In contrast to the CCR3/eotaxin system which is mainly regulated at the level of ligand production, the CXCR4/SDF-1 system is regulated at the level of receptor expression. CXCR4 expression was completely attenuated by IL-4 and IL-5 and upregulated by IFN-gamma and dexamethasone, while CCR3 expression was only marginally affected. The balance between the biological effects of these chemokine systems may affect the distribution and migration of eosinophils.