Prostaglandin E2 in tick saliva regulates macrophage cell migration and cytokine profile

Nina M Poole,Lewis B Coons,Gayatri Mamidanna,Judith A Cole,Richard A Smith

doi:10.1186/1756-3305-6-261

Abstract

BackgroundTicks are obligate hematophagous ectoparasites that suppress the host’s immune and inflammatory responses by secreting immuno-modulatory and anti-inflammatory molecules in their saliva. In previous studies we have shown that tick salivary gland extract (SGE) and saliva from Dermacentor variabilis have distinct effects on platelet-derived growth factor (PDGF)-stimulated IC-21 macrophage and NIH3T3-L1 fibroblast migration. Since tick saliva contains a high concentration of prostaglandin E2 (PGE2), a potent modulator of inflammation, we used a PGE2 receptor antagonist to evaluate the role of PGE2 in the different migratory responses induced by saliva and its impact on macrophage cytokine profile.MethodsAdult ticks were fed on female New Zealand white rabbits for 5-8 days. Female ticks were stimulated with dopamine/theophylline to induce salivation and saliva was pooled. Competitive enzyme immunoassays (EIA) were used to measure saliva PGE2 content and the changes in macrophage intracellular cyclic adenosine monophosphate (cAMP) levels. The effects of tick saliva on macrophage and fibroblast migration were assessed in the absence and presence of the PGE2 receptor antagonist, AH 6809, using blind well chamber assays. A cytokine antibody array was used to examine the effects of tick saliva on macrophage cytokine secretion. Statistical significance was determined by one-way ANOVA; Student Newman-Kuels post-test was used for multiple comparisons.ResultsThe saliva-induced increase in PDGF-stimulated macrophage migration was reversed by AH 6809. The inhibition of PDGF-stimulated fibroblast migration by saliva was also antagonist-sensitive. Tick saliva induced macrophages to secrete copious amounts of PGE2, and conditioned medium from these cells caused an AH 6809-sensitive inhibition of stimulated fibroblast migration, showing that macrophages can regulate fibroblast activity. We show that tick saliva decreased the secretion of the pro-inflammatory cytokines regulated and normal T cell expressed and secreted (RANTES/CCL5), tumor necrosis factor-alpha (TNF-α), and soluble TNF receptor I (sTNFRI) through a PGE2-dependent mechanism mediated by cAMP. Saliva had similar effects on lipopolysaccharide (LPS) stimulated macrophages.ConclusionsOur data show that ticks utilize salivary PGE2 to subvert the ability of macrophages to secrete pro-inflammatory mediators and recruit fibroblasts to the feeding lesion, therefore inhibiting wound healing.

Highlights

Ticks are obligate hematophagous ectoparasites that suppress the host’s immune and inflammatory responses by secreting immuno-modulatory and anti-inflammatory molecules in their saliva
This reduction was similar to the effects observed in cells treated with prostaglandin E2 (PGE2) in the presence of the receptor antagonist 58 ± 32% (Figure 2A) which suggests the saliva-induced increase in macrophage migration was mediated by PGE2
The inhibitory effects of saliva and macrophage conditioned medium were similar to that of PGE2 and were antagonized by AH 6809 (Figure 2B). This antagonism partially restored the migration of the saliva-treated cells 55 ± 17% while there was full restoration in the cells treated with conditioned medium from saliva-treated macrophages 94 ± 21% when compared to the platelet-derived growth factor (PDGF)-stimulated cells (Figure 2B)

Summary

Introduction

Ticks are obligate hematophagous ectoparasites that suppress the host’s immune and inflammatory responses by secreting immuno-modulatory and anti-inflammatory molecules in their saliva. Since tick saliva contains a high concentration of prostaglandin E2 (PGE2), a potent modulator of inflammation, we used a PGE2 receptor antagonist to evaluate the role of PGE2 in the different migratory responses induced by saliva and its impact on macrophage cytokine profile. Ixodid ticks such as Dermacentor variabilis are obligate blood-sucking ectoparasites that physically attach to their host for several days to feed until repletion. Tick saliva contains molecules that control host angiogenesis and wound healing to aid feeding [34,35,36,37,38]

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