The Biologic Role of Interleukin-8: Functional Analysis and Expression of CXCR1 and CXCR2 on Human Eosinophils

Abstract

Chemokines play an important role in attracting granulocytes into sites of inflammation. Two chemokine subfamilies differ in their biologic activity for different granulocyte subsets. Whereas CXC chemokines such as interleukin-8 (IL-8) activate predominantly neutrophils, CC chemokines such as RANTES and eotaxin activate predominantly eosinophils. However, controversial results have been published in the past regarding the biologic role of IL-8 in eosinophil activation, particularly in allergic diseases. In this study, we investigated the functional evidence and expression of both IL-8 receptors, 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 neutrophils and lymphocytes, IL-8 did not induce a rapid and transient release of cytosolic free Ca2+([Ca2+]i) in eosinophils, even after preincubation with TH1- and TH2-like cytokines. To investigate whether neutrophil contamination might be responsible for the reported IL-8 effects on eosinophils, neutrophils were added to highly purified eosinophils from the same donor in different concentrations. Interestingly, as little as 5% of neutrophil contamination was sufficient to induce an increase of [Ca2+]iafter stimulation with IL-8. Flow cytometry experiments with monoclonal antibodies against both IL-8 receptors demonstrated no expression of CXCR1 and CXCR2 on eosinophils before or after cytokine activation. Reverse transcriptase-polymerase chain reaction experiments showed that eosinophils, in contrast to neutrophils and lymphocytes, did not express mRNA for CXCR1 and CXCR2. In summary, this study clearly demonstrates that CXCR1 and CXCR2 are not expressed on human eosinophils, even after priming with different bioactive cytokines. Because the CXC chemokine IL-8 did not induce in vitro effects on human eosinophils, IL-8 may also not contribute in vivo to the influx of eosinophil granulocytes into sites of allergic inflammation. Our results suggest that CC chemokines such as eotaxin, eotaxin-2, and MCP-4 are predominant for the activation of eosinophils.

The selective nonpeptide CXCR2 antagonist SB225002 ameliorates acute experimental colitis in mice

“…Although SB225002 administration inhibited MPO activity, it failed to reduce EPO activity, suggesting that eosinophil infiltration was not altered by CXCR2 antagonism. In agreement with this data, it has been shown that CXCR2 is not expressed on the eosinophil surface [32]. The relevance of eosinophils in gut inflammation has been described by several authors [33].…”

The CC chemokine receptor 3 CCR3 is functionally expressed on eosinophils but not on neutrophils

“…One representative experiment out of five is shown. studies, we and others could clearly demonstrate that eosinophils do not functionally express IL-8R [3,19]. Most of these conflicting results could be explained due to contaminating neutrophils in the eosinophil preparation at which less than 5% of neutrophil contamination is sufficient to induce a [Ca 2+ ] i signal in human eosinophils stimulated with IL-8 [3].…”

“…In the case of granulocytes, CC chemokine receptors such as CCR3 are expressed by eosinophils, whereas CXC chemokine receptors such as CXCR1 and CXCR2 are expressed by neutrophils [3]. Apart from the expres-sion of CCR3 on eosinophils, recent studies have demonstrated that CCR3 could also be detected on various cell types including basophils [4], microglia cells [5] and IFN-+ -treated monocytes [6].…”

ORIGINAL ARTICLE: CXCL6 (Granulocyte Chemotactic Protein‐2): A Novel Chemokine Involved in the Innate Immune Response of the Amniotic Cavity

“…44 Neither CXCR1 nor CXCR2 have been localized on B cells or eosinophils. [45][46][47][48] Of interest, although CXCL6 was first discovered in a malignant cell-line, tumor cells are poor producers of this chemokine. High levels of CXCL6 mRNA have been identified in the heart, lung, liver, and pancreas, while only weak expression has been found in the brain, kidney, and placenta.…”