The biologic role of interleukin-8: Functional analysis and expression of CXCR1 and CXCR2 on human eosinophils

Chemokines play an important role in attracting granulocytes into sites of inflammation. Two chemokine subfamilies differ in their biologic activity f or different granulocyte subsets. Whereas CXC chemokines such as interleuki n-8 (IL-8) activate predominantly neutrophils, CC chemokines such as RANTES and eotaxin activate predominantly eosinophils. However, controversial res ults have been published in the past regarding the biologic role of IL-8 in eosinophil activation, particularly in allergic diseases. In this study, w e investigated the functional evidence and expression of both IL-8 receptor s, CXCR1 and CXCR2, on highly purified human eosinophils. In the first set of experiments, a chemotaxis assay was performed showing that IL-8 did not induce chemotaxis of eosinophils. In addition, and in contrast to neutrophi ls and lymphocytes, IL-8 did not induce a rapid and transient release of cy tosolic free Ca2+ ([Ca2+](i)) in eosinophils, even after preincubation with TH1- and TH2-like cytokines. To investigate whether neutrophil contaminati on might be responsible for the reported IL-8 effects on eosinophils, neutr ophils were added to highly purified eosinophils from the same donor in dif ferent concentrations. interestingly, as little as 5% of neutrophil contami nation was sufficient to induce an increase of [Ca2+](i) after stimulation with IL-8. Flow cytometry experiments with monoclonal antibodies against bo th IL-8 receptors demonstrated no expression of CXCR1 and CXCR2 on eosinoph ils before or after cytokine activation. Reverse transcriptase-polymerase c hain reaction experiments showed that eosinophils, in contrast to neutrophi ls and lymphocytes, did not express mRNA for CXCR1 and CXCR2. In summary, t his study clearly demonstrates that CXCR1 and CXCR2 are not expressed on hu man eosinophils, even after priming with different bioactive cytokines. Bec ause the CXC chemokine IL-8 did not induce in vitro effects on human eosino phils, IL-8 may also not contribute in vivo to the influx of eosinophil gra nulocytes into sites of allergic inflammation. Our results suggest that GC chemokines such as eotaxin, eotaxin-2, and MCP-4 are predominant for the ac tivation of eosinophils. (C) 1999 by The American Society of Hematology.