Immunomodulatory effects of Ixodes ricinus tick saliva on the host and their role in tick-borne pathogen transmission. Development of pathogen transmission-blocking vaccines.
Chmelař J., Oliveira C.J., Řezáčová P., Francischetti I.M., Kovářová Z., Pejler G., Kopáček P., Ribeiro J.M., Mareš M., Kopecký J., Kotsyfakis M. (2011) A tick salivary protein targets cathepsin G and chymase and inhibits host inflammation and platelet aggregation. Blood 117: 736–744.
Růžek D., Salát J., Singh S.K., Kopecký J. (2011) Breakdown of the blood-brain barrier during tick-borne encephalitis in mice is not dependent on CD8+ T-cells. PLOS One 6: e20472.
Salát J., Paesen G.C., Řezáčová P., Kotsyfakis M., Kovářová Z., Šanda M., Majtán J., Grunclová L., Horká H., Andersen J.F., Brynda J., Horn M., Nunn M.A., Kopáček P., Kopecký J., Mareš M. (2010) Crystal structure and functional characterization of an immunomodulatory salivary cystatin from the soft tick Ornithodoros moubata. Biochemical Journal 429: 103–112.
Fialová A., Cimburek Z., Iezzi G., Kopecký J. (2010) Ixodes ricinus tick saliva modulates tick-borne encephalitis virus infection of dendritic cells. Microbes and Infection 12: 580–585.
Růžek D., Yakimenko V.V., Karan L.S., Tkachev S.E. (2010) Omsk haemorrhagic fever. The Lancet 376: 2104–2113.
Effect of tick sdaliva on dendritic cells
To extend the knowledge about the impact of the I. ricinus tick saliva on dendritic cells (DCs), we have examined effects of the saliva on DC maturation and migration, and on DC-mediated priming and polarization of naive CD4+ T cells. The tick saliva promoted an inhibition of synthetic TLR ligands-induced DC maturation in vitro, as well as dibutyl phthalate (DBP)-induced DC maturation in vivo. Using a sensitive in vitro priming system, we have demonstrated that the saliva significantly diminished IFN-? and IL 17 production, and increased IL-4 production by transgenic CD4+ T cells. Moreover, in contrast to controls, in the co-cultures of naive transgenic CD4+ T cells with in vivo saliva-stimulated DCs, Th2 cells markedly prevailed over the Th1 cells. The tick saliva also inhibited the early phase of DBP-induced DC migration from skin into draining lymph nodes. Our data demonstrate a complex impact of the tick saliva on DC phenotype and function, which might be the key mechanism used by the tick to evade host immune system.
Salivary cystatin from the soft tick Ornithodoros moubata (OmC2)
Recombinant OmC2 was screened against a panel of physiologically relevant peptidases and found to be an effective broad-specificity inhibitor of cysteine cathepsins, including endopeptidases (cathepsins L and S) and exopeptidases (cathepsins B, C and H). The crystal structure of OmC2 was determined at a resolution of 2.45 A and used to describe the structure-inhibitory activity relationship. The potential biological impact of OmC2 on the host-parasite interaction was demonstrated in two types of experiments. First, OmC2 displayed in vitro immunomodulatory activity: it affected the function of antigen-presenting mouse dendritic cells by reducing the production of the proinflammatory cytokines TNF-alfa and IL-12, and the proliferation of antigen-specific CD4+ T cells. Second, immunization of mice with OmC2 significantly suppressed the survival of O. moubata ticks in infestation experiments.
Interaction of Borrelia spirochetes with macrophages
The effect of salivary gland extracts (SGE) and saliva from the tick I. ricinus on the interaction of B. afzelii spirochetes with mouse macrophages as well as on the borreliacidal effect of calf serum was studied. SGE reduced both the number of phagocytosing cells and phagocytosed bacteria. An inhibitory effect of SGE on the killing of spirochetes by the alternative pathway of complement activation was also observed. Both SGE and saliva down-regulated production of pro-inflammatory cytokine TNF-? by macrophages stimulated with IFN-? and live B. afzelii spirochetes. SGE and saliva exerted a different effect on the production of nitric oxide by stimulated macrophages. Whereas SGE up-regulated NO production, saliva decreased it.
Saliva-activated transmission of Borrelia burgdorferi
Tick saliva-activated transmission of the Lyme disease agent, Borrelia burgdorferi sensu lato, was also studied. Using Real-Time PCR, the accelerating effect of SGE or saliva on the proliferation of B. burgdorferi in the mouse skin and other organs (heart, urinary bladder) was demonstrated. The prevalence of spirochetes in ticks infected by feeding on mice was more than 10 times higher when the mice were infected with the mixture of spirochetes and saliva or SGE, in comparison with spirochetes alone. The presence of SGE in the infectious inoculum increased the spirochete burden per tick from 0 to almost 28,000. Taken together, these results show a very early effect of tick saliva on the proliferation and distribution of Borrelia spirochetes in the host, probably due to the effect of saliva on the host innate immunity mechanisms.
Saliva-activated transmission activity of tick cystatins
Sialostatin L2 from I. scapularis accelerated proliferation of B. burgdorferi spirochetes when injected together with the pathogen. A four-fold increase of spirochete count was recorded in the inoculation site (skin). Sialostatin L2 seems to be the second known SAT factor identified so far.
A large collection of helminths is available for comparative studies...
