Saliva of Ixodes ricinus enhances TBE virus replication in dendritic cells by modulation of pro-survival Akt pathway.

It has been suggested that tick saliva facilitates transmission of tick-borne encephalitis virus (TBEV) to vertebrates. The mechanism of this facilitation has not been elucidated yet. Since dendritic cells (DCs) are among first cells attacked by the virus, we examined the amount of virus and changes induced by saliva in TBEV-infected DCs. We found that virus replication was significantly increased by saliva of Ixodes ricinus tick. Next, saliva-induced enhancement of Akt pathway activation was observed in TBEV-infected DCs. Akt mediated pathway is known for its anti-apoptotic and pro-survival effects. Accordingly, apoptosis of TBEV-infected DCs was declined and cellular viability increased in the presence of tick saliva. Saliva-induced enhancement of STAT1 and NF-κB was also observed in TBEV-infected DCs. In conclusion, we suggest that tick saliva provides pro-survival and anti-apoptotic signals to infected DCs via upregulation of Akt, which may have positive consequences for TBEV replication and transmission.

Tick sialostatins L and L2 differentially influence dendritic cell responses to Borrelia spirochetes.

BACKGROUND: Transmission 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. METHODS: DCs 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-ß 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. RESULTS: We 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-ß 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-ß in pDC and also impaired the maturation of these cells. CONCLUSIONS: This 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.

Ixodes ricinus salivary serpin IRS-2 affects Th17 differentiation via inhibition of the interleukin-6/STAT-3 signaling pathway.

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.