Tick saliva suppresses IFN signalling in dendritic cells upon Borrelia afzelii infection

Type I interferons (IFN-α and IFN-β) are crucial determinants of the host immune response and tick saliva modulates this response, thus facilitating the transmission of tickborne pathogens. The current study therefore examines the effect of Ixodes ricinus tick saliva on IFN-β signalling in murine dendritic cells using lipopolysaccharide (LPS) and Borrelia afzelii spirochaetes as inducers. Activated dendritic cells secret IFN that activates Signal Transducer and Activator of Transcription 1 (STAT-1). Our results show that Borrelia-induced activation of STAT-1 was suppressed by tick saliva. As the amount of secreted IFN-β was not influenced by tick saliva, the results indicated that saliva affected the interferon pathway at the IFN receptor or downstream of it. By using recombinant IFN-β, we show that tick saliva attenuates IFN-triggered STAT-1 activation. Tick saliva also inhibited LPS-induced IFN-β production suggesting that saliva interferes with the activation of the pathway that mediates IFN-β induction. Our data indicate that I. ricinus tick saliva may modulate the host immune response by attenuating the initial signal transduction pathway of type I IFN.