Tick saliva has been shown to modulate host immunity by a so far unknown mechanism. We have demonstrated an inverted effect of salivary gland extract (SGE), derived from partially fed Ixodes ricinus females, on the production of two cytokines, interferon (IFN)‐γ and interleukin (IL)‐10, in vitro. While SGE markedly suppressed the elaboration of IFN‐γ by mouse splenocytes stimulated with lipopolysaccharide (LPS), the production of IL‐10 was increased in comparison with SGE‐untreated cultures. The suppressive effect of SGE could be abolished by the addition of an IL‐10 neutralizing monoclonal antibody to splenocyte cultures. Similar results were obtained when live Borrelia afzelii spirochetes, which are transmitted in Europe by I. ricinus ticks, were used for the cytokine induction. These results suggest that tick saliva can upregulate the IL‐10 production at the tick feeding site, which consecutively inhibits the elaboration of pro‐inflammatory cytokines, for example IFN‐γ. This immunosuppression may facilitate the establishment of tick‐transmitted pathogens in the host.

Salivary gland extract (SGE) from Ixodes ricinus ticks inhibited the killing of Borrelia afzelii spirochetes by murine macrophages. SGE also reduced the production of two major defense molecules of phagocytes, superoxide and nitric oxide. It is likely that the suppression of macrophage microbicidal mechanisms contributes to the inhibitory effect of tick saliva on the killing of B. afzelii spirochetes, thus facilitating the transmission of this important pathogen.

No abstract