Next generation sequencing and proteomics have helped to comprehensively characterize gene expression in tick salivary glands at both the transcriptome and the proteome level. Functional data are, however, lacking. Given that tick salivary secretions are critical to the success of the tick transmission lifecycle and, as a consequence, for host colonization by the pathogens they spread, we thoroughly review here the literature on the known interactions between tick saliva (or tick salivary gland extracts) and the innate and adaptive vertebrate immune system. The information is intended to serve as a reference for functional characterization of the numerous genes and proteins expressed in tick salivary glands with an ultimate goal to develop novel vector and pathogen control strategies.

Insulin-like growth factor I (IGF-I) stimulates smooth muscle cell (SMC) proliferation, and the mitogen-activated protein kinase (MAPK) pathway plays an important role in mediating IGF-I-induced mitogenic signaling. Our prior studies have shown that recruitment of Src homology 2 domain tyrosine phosphatase (SHP-2) to the membrane scaffolding protein Src homology 2 domain-containing protein tyrosine phosphatase substrate-1 (SHPS-1) is required for IGF-I-dependent MAPK activation. The current studies were undertaken to define the upstream signaling components that are required for IGF-I-stimulated MAPK activation and the role of SHPS-1 in regulating this process. The results show that IGF-I-induced Shc phosphorylation and its subsequent binding to Grb2 is required for sustained phosphorylation of MAPK and increased cell proliferation in SMCs. Furthermore, for Shc to be phosphorylated in response to IGF-I requires that Shc must associate with SHPS-1 and this association is mediated in part by SHP-2. Preincubation of cells with a peptide that contains a phospho-tyrosine binding motif sequence derived from SHPS-1 inhibited IGF-I-stimulated SHP-2 transfer to SHPS-1, the association of Shc with SHPS-1, and IGF-I-dependent Shc phosphorylation. Expression of an SHPS-1 mutant that did not bind to Shc or SHP-2 resulted in decreased Shc and MAPK phosphorylation in response to IGF-I. In addition, SMCs expressing a mutant form of the ␤3 subunit of the ␣V␤3, which results in impairment of SHP-2 transfer to SHPS-1, also showed attenuated IGF-I-dependent Shc and MAPK phosphorylation. Further analysis showed that Shc and SHP-2 can be coimmunoprecipitated after IGF-I stimulation. A cell-permeable peptide that contained a polyproline sequence from Shc selectively inhibited Shc/SHP-2 association and impaired Shc but not SHP-2 binding to SHPS-1. Exposure to this peptide also inhibited IGF-I-stimulated Shc and MAPK phosphorylation. Cells expressing a mutant form of Shc with the four prolines substituted with alanines showed no Shc/SHPS-1 association in response to IGF-I. We conclude that SHPS-1 functions as an anchor protein that recruits both Shc and SHP-2 and that their recruitment is necessary for IGF-Idependent Shc phosphorylation, which is required for an optimal mitogenic response in SMCs. INTRODUCTIONBoth vascular smooth muscle cell proliferation and migration in response to growth factor stimulation play important roles in the formation of atherosclerotic plaques, and insulin-like growth factor I (IGF-I) is a potent stimulator of smooth muscle cell proliferation and migration (Jones et al., 1996). In primary cultured smooth muscle cells (pSMCs), IGF-I induces activation of both the phosphatidylinositol (PI)-3 kinase and the mitogen-activated protein (MAP) kinase (MAPK) pathways. Both pathways have been shown to play roles in mediating IGF-I-dependent cell migration and cell proliferation responses (Imai and Clemmons, 1999;Maile et al., 2003).Previous studies have shown that the protein tyrosine phosphatase SHP-2 plays an impor...

Macrophage-mediated phagocytosis and cytokine production represent the front lines of resistance to bacterial invaders. A key feature of this pro-inflammatory response in mammals is the complex remodeling of cellular metabolism towards aerobic glycolysis. Although the function of bactericidal macrophages is highly conserved, the metabolic remodeling of insect macrophages remains poorly understood. Here, we used adults of the fruit fly Drosophila melanogaster to investigate the metabolic changes that occur in macrophages during the acute and resolution phases of Streptococcus-induced sepsis. Our studies revealed that orthologs of Hypoxia inducible factor 1α (HIF1α) and Lactate dehydrogenase (LDH) are required for macrophage activation, their bactericidal function, and resistance to infection, thus documenting the conservation of this cellular response between insects and mammals. Further, we show that macrophages employing aerobic glycolysis induce changes in systemic metabolism that are necessary to meet the biosynthetic and energetic demands of their function and resistance to bacterial infection.

Activation of the MAPK pathway mediates insulin-like growth factor-I (IGF-I)-dependent proliferation in vascular smooth muscle cells (SMC).Our previous studies have shown that IGF-I-induced Shc phosphorylation is necessary for sustained activation of MAPK and increased cell proliferation of SMCs, and both Shc and the tyrosine phosphatase SHP-2 must be recruited to the membrane protein SHPS-1 in order for Shc to be phosphorylated. These studies were undertaken to determine whether Src kinase activity is required to phosphorylate Shc in response to IGF-I in SMC and because SHP-2 binds to Src whether their interaction was also required for IGF-I-stimulated mitogenesis. Our results show that IGF-I induces activation of Src kinase and that is required for Shc phosphorylation and for optimal MAPK activation. We tested whether Shc is a substrate of c-Src in SMC by disrupting Src/Shc association using a peptide containing a YXXL (Tyr 328 ) motif sequence derived from Src. The peptide blocked the binding of Src and Shc in vitro and in vivo. Cells expressing a mutant Src (Src-FF) that had Tyr 328 / Tyr 358 substituted with phenylalanines (Src-FF) showed defective Src/Shc binding, impaired IGF-I-dependent Shc phosphorylation, and impaired mitogenesis. This supports the conclusion that Src phosphorylates Shc. IGF-I induced both Src/SHP-2 and Src/SHPS-1 association. SMCs expressing an SHP-2 mutant that had the polyproline-rich region of SH2 deleted (SHP-2⌬10) had disrupted SHP-2/Src association, impaired IGF-I-dependent Shc phosphorylation, and an attenuated mitogenic response. IGF-I-induced association of Src and SHPS-1 was also impaired in SHP-2⌬10-expressing cells, although SHP-2/SHPS-1 association was unaffected. Upon IGF-I stimulation, a complex assembles on SHPS-1 that contains SHP-2, c-Src, and Shc wherein Src phosphorylates Shc, a signaling step that is necessary for an optimal mitogenic response. IGF-I2 stimulation of vascular smooth muscle cells (SMC) leads to activation of two major signaling pathways, e.g. the MAP kinase (MAPK) and PI 3-kinase pathways (1). Activation of the MAPK pathway is required for IGF-I-dependent proliferation, whereas activation of the PI 3-kinase pathway is the predominant determinant of IGF-I-dependent SMC migration. BindingofIGF-ItotheIGF-Ireceptorleadstoreceptorautophosphorylation followed by tyrosine phosphorylation of substrates such as IRS-1 and Shc (2). These adaptor proteins bind Grb2/ SOS and activate the Ras/MAPK pathway (3). Previous studies in SMC have shown that IGF-I-induced Shc phosphorylation and its association with Grb-2 are necessary for sustained phosphorylation of Erk1/2 MAPK and IGF-I-dependent cell proliferation (4). The requirement of Shc phosphorylation for growth factor-dependent mitogenesis has been demonstrated in other cell types as well (5, 6).Src family kinases (SFK) have been implicated in mediating the mitogenic effect of several growth factors (7, 8); however, the mechanism by which SFK function is not completely understood. Src has also been implicated i...

Type I interferon (IFN), mainly produced by dendritic cells (DCs), is critical in the host defence against tick-transmitted pathogens. Here, we report that salivary cysteine protease inhibitor from the hard tick Ixodes scapularis, sialostatin L2, affects IFN-β mediated immune reactions in mouse dendritic cells. Following IFN receptor ligation, the Janus activated kinases/signal transducer and activator of transcription (JAK/STAT) pathway is activated. We show that sialostatin L2 attenuates phosphorylation of STATs in spleen dendritic cells upon addition of recombinant IFN-β. LPS-stimulated dendritic cells release IFN-β which in turn leads to the induction of IFN-stimulated genes (ISG) through JAK/STAT pathway activation. The induction of two ISG, interferon regulatory factor 7 (IRF-7) and IP-10, was suppressed by sialostatin L2 in LPS-stimulated dendritic cells. Finally, the interference of sialostatin L2 with IFN action led to the enhanced replication of tick-borne encephalitis virus in DC. In summary, we present here that tick salivary cystatin negatively affects IFN-β responses which may consequently increase the pathogen load after transmission via tick saliva.

c Th17 cells constitute a subset of CD4؉ T lymphocytes that play a crucial role in protection against extracellular bacteria and fungi. They are also associated with tissue injury in autoimmune and inflammatory diseases. Here, we report that serpin from the tick Ixodes ricinus, IRS-2, inhibits Th17 differentiation by impairment of the interleukin-6 (IL-6)/STAT-3 signaling pathway. Following activation, mature dendritic cells produce an array of cytokines, including the pleiotropic cytokine IL-6, which triggers the IL-6 signaling pathway. The major transcription factor activated by IL-6 is STAT-3. We show that IRS-2 selectively inhibits production of IL-6 in dendritic cells stimulated with Borrelia spirochetes, which leads to attenuated STAT-3 phosphorylation and finally to impaired Th17 differentiation. The results presented extend the knowledge about the effect of tick salivary serpins on innate immunity cells and their function in driving adaptive immune responses. Ticks are bloodsucking arthropods, major vectors of human pathogens like Borrelia burgdorferi and tick-borne encephalitis virus. Ticks from the family Ixodidae (hard ticks) require several days to fully engorge. During feeding, ixodid ticks remain tightly attached to their host (1, 2). To avoid attack from the host immune system during the feeding period, tick saliva contains two groups of molecules, the first with antihemostatic and the second with immunomodulatory properties. These groups include both proteinaceous and nonprotein molecules (3). One group of immunomodulatory proteins is represented by serine proteinase inhibitors (serpins), a large superfamily of structurally related, but functionally diverse, proteins that control essential proteolytic pathways (4, 5). Recently, three serine protease inhibitors, namely, purified human urinary trypsin inhibitor (UTI) and two synthetic serpins, gabextate mesilate (FOY) and nafamostat mesilate (FUT), which are widely used in treatment of acute inflammatory disorders, such as disseminated intravascular coagulation (DIC), have been shown to attenuate allergic airway inflammation and remodeling in a murine model of chronic asthma. These effects were associated with inhibition of Th2 cytokines (interleukin-4 [IL-4], IL-5, IL-6, and IL-13) and Th17 cell functions. These serpins also inhibited NF-B activation in lung tissues (6).Until now, more than 60 serpins have been identified at the sequence level in ixodid ticks, but only two serpins from Ixodes ricinus have been further functionally characterized (7-9). The first known I. ricinus serpin, Iris (I. ricinus immunosuppressor), is known to preferentially target leukocyte elastase. It also interferes with the contact phase coagulation pathway, fibrinolysis, and disrupts platelet adhesion. Moreover, Iris has the ability to modulate both innate and adaptive immunity. It affects T lymphocyte and macrophage responsiveness, and it induces a Th2-type response and inhibits the production of proinflammatory cytokines. Interestingly, it was shown that the anti-inf...

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BackgroundTransmission of pathogens by ticks is greatly supported by tick saliva released during feeding. Dendritic cells (DC) act as immunological sentinels and interconnect the innate and adaptive immune system. They control polarization of the immune response towards Th1 or Th2 phenotype. We investigated whether salivary cystatins from the hard tick Ixodes scapularis, sialostatin L (Sialo L) and sialostatin L2 (Sialo L2), influence mouse dendritic cells exposed to Borrelia burgdorferi and relevant Toll-like receptor ligands.MethodsDCs derived from bone-marrow by GM-CSF or Flt-3 ligand, were activated with Borrelia spirochetes or TLR ligands in the presence of 3 μM Sialo L and 3 μM Sialo L2. Produced chemokines and IFN-β were measured by ELISA test. The activation of signalling pathways was tested by western blotting using specific antibodies. The maturation of DC was determined by measuring the surface expression of CD86 by flow cytometry.ResultsWe determined the effect of cystatins on the production of chemokines in Borrelia-infected bone-marrow derived DC. The production of MIP-1α was severely suppressed by both cystatins, while IP-10 was selectively inhibited only by Sialo L2. As TLR-2 is a major receptor activated by Borrelia spirochetes, we tested whether cystatins influence signalling pathways activated by TLR-2 ligand, lipoteichoic acid (LTA). Sialo L2 and weakly Sialo L attenuated the extracellular matrix-regulated kinase (Erk1/2) pathway. The activation of phosphatidylinositol-3 kinase (PI3K)/Akt pathway and nuclear factor-κB (NF-κB) was decreased only by Sialo L2. In response to Borrelia burgdorferi, the activation of Erk1/2 was impaired by Sialo L2. Production of IFN-β was analysed in plasmacytoid DC exposed to Borrelia, TLR-7, and TLR-9 ligands. Sialo L, in contrast to Sialo L2, decreased the production of IFN-β in pDC and also impaired the maturation of these cells.ConclusionsThis study shows that DC responses to Borrelia spirochetes are affected by tick cystatins. Sialo L influences the maturation of DC thus having impact on adaptive immune response. Sialo L2 affects the production of chemokines potentially engaged in the development of inflammatory response. The impact of cystatins on Borrelia growth in vivo is discussed.Electronic supplementary materialThe online version of this article (doi:10.1186/s13071-015-0887-1) contains supplementary material, which is available to authorized users.