CXCL8 attenuates chemoattractant-induced equine neutrophil migration.
The chemokine, CXCL8, is a potent chemoattractant but it has also been shown to attenuate the migratory response of human neutrophils to the bacterial peptide, FMLP; this could lead to retention of cells in infected tissue and, potentially, to enhanced clearance of bacteria. This study has examined the effect of CXCL8 on equine neutrophil migration and adherence in response to PAF and LTB(4), chemoattractants that may play a role in non-infectious inflammatory conditions of the horse associated with neutrophil recruitment to the target tissue. The effects of CXCL8 on PAF- and LTB(4)-induced responses were determined using a ChemoTx plate migration assay and by measuring adhesion to protein-coated plastic. The CXCR1/2 antagonist, SB225002, was used to investigate whether the observed effects were receptor mediated and the role of cAMP was examined by measuring intracellular cAMP following exposure to agonists alone and in combination and by establishing the effect of dibutyryl cAMP on neutrophil migration. CXCL8, LTB(4) and PAF each induced migration and adhesion. Exposure of neutrophils to a combination of CXCL8 and PAF reduced the magnitude of the responses to that of unstimulated cells. In contrast, although the effect was less than additive, the response to co-stimulation with CXCL8 and LTB(4) were not nearly as pronounced. CXCL8 acted in a receptor mediated manner, the attenuation of PAF-induced responses being reversed by SB225002 at a concentration that blocks CXCR2. CXCL8, PAF and LTB(4) alone increased intracellular cAMP. In co-incubation studies, combination of CXCL8 with PAF led to an additive increase in cAMP whereas no increase above that obtained in response to LTB(4) alone was seen. Dibutyryl cAMP significantly reduced neutrophil migration in response to either CXCL8 or PAF alone. These results demonstrate that CXCL8, in addition to being a potent chemoattractant and pro-adhesive molecule for equine neutrophils, is able to attenuate responses to PAF and, to a much lesser extent, LTB(4). This effect, which appears to be CXCR2-mediated and cAMP dependent, could lead in vivo to trapping of cells at sites of inflammation resulting potentially in either enhanced clearance of injurious stimuli or increased local tissue damage by activated cells.
Department of Veterinary Basic Sciences, Royal Veterinary College, Hawkshead Lane, North Mymms, Hertfordshire, AL9 7TA, UK. abrooks@rvc.ac.uk
Andrew C
AC
Brooks
Karen J
KJ
Rickards
Fiona M
FM
Cunningham
D000818:Animals; D002448:Cell Adhesion; D002465:Cell Movement / Q000187:drug effects*; D002478:Cells, Cultured; D002630:Chemotactic Factors / Q000494:pharmacology; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP; D006736:Horses; D016209:Interleukin-8 / Q000494:pharmacology*; D007975:Leukotriene B4 / Q000494:pharmacology*; D009504:Neutrophils / Q000187:drug effects* / Q000502:physiology*; D010972:Platelet Activating Factor / Q000494:pharmacology*
D002630:Chemotactic Factors; D016209:Interleukin-8; D010972:Platelet Activating Factor; D005576:Colforsin; D007975:Leukotriene B4; D000242:Cyclic AMP