Neutrophils play a pivotal role in the innate immune response. The small cytokine CXCL8 (also known as IL-8) is known to be one of the most potent chemoattractant molecules that, among several other functions, is responsible for guiding neutrophils through the tissue matrix until they reach sites of injury. Unlike mice and rats that lack a CXCL8 homolog, zebrafish has two distinct CXCL8 homologs: Cxcl8-l1 and Cxcl8-l2. Cxcl8-l1 is known to be upregulated under inflammatory conditions caused by bacterial or chemical insult but until now the role of Cxcl8s in neutrophil recruitment has not been studied. In this study we show that both Cxcl8 genes are upregulated in response to an acute inflammatory stimulus, and that both are crucial for normal neutrophil recruitment to the wound and normal resolution of inflammation. Additionally, we have analyzed neutrophil migratory behavior through tissues to the site of injury in vivo, using open-access phagocyte tracking software PhagoSight. Surprisingly, we observed that in the absence of these chemokines, the speed of the neutrophils migrating to the wound was significantly increased in comparison with control neutrophils, although the directionality was not affected. Our analysis suggests that zebrafish may possess a subpopulation of neutrophils whose recruitment to inflamed areas occurs independently of Cxcl8 chemokines. Moreover, we report that Cxcl8-l2 signaled through Cxcr2 for inducing neutrophil recruitment. Our study, therefore, confirms the zebrafish as an excellent in vivo model to shed light on the roles of CXCL8 in neutrophil biology.
This work was supported by Fundação para a Ciência e Tecnologia via Ph.D. Fellowship Grant SFRH/BD/62674/2009 (to S.d.O.), Spanish Ministry of Science and Innovation through Grants BIO2011-23400 and CSD2007-00002 cofunded with the Fondo Europeo de Desarrollo Regional/European Regional Developmental Fund (to V.M.) and a Ph.D. fellowship (to S.C.), and by Fundación Séneca-Murcia via Grant 04538/GERM/06 (to V.M.). S.A.R. is funded by U.K. Medical Research Council Senior Clinical Fellowship G0701932 and Medical Research Council Centre Grant G0700091.
The online version of this article contains supplemental material.
Abbreviations used in this article:
- days postfertilization
- hours postwounding
- leukotriene B4
- quantitative PCR
- ribosomal protein S11 gene
- standard control
- Received November 28, 2012.
- Accepted February 19, 2013.
- Copyright © 2013 by The American Association of Immunologists, Inc.