Salivary gland extract from Ixodes ricinus ticks inhibits production of interferon-γ by the upregulation of interleukin-10

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)-gamma and interleukin (IL)-10, in vitro. While SGE markedly suppressed the elaboration of IFN-gamma 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 sicks, 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-gamma. This immunosuppression may facilitate the establishment of tick-transmitted pathogens in the host.