Salivary gland extracts of different partially fed ticks affect human natural killer cell activity in different manner

The salivary glands and saliva of ticks play a vital role in blood feeding, including manipulation of the host's response to tick infestation. Furthermore, a diverse number of tick-borne pathogens are transmitted to vertebrate hosts via tick saliva. We show that salivary gland extracts (SGE) derived from Dermacentor reticulatus female or male ticks fed different times on laboratory mice, induced a decrease in the natural killer activity (NKA) of effector cells obtained from healthy blood donors, in a time dependent manner. Such a decrease was not observed after treatment of effector cells with SGE from unfed ticks. Similarly, SGE derived from Amblyomma variegatum female ticks fed 14 days decreased NKA. In contrast, SGE derived from Rhipicephalus appendiculatus female ticks fed for 3 or 5 days on mice increased NKA. After addition of IFN-alpha 2, the SGE-induced decrease in NKA was restored to activity levels approaching those of untreated cells. The results demonstrate the presence of a factor(s) in tick salivary glands that influence human effector cells in their natural killer activity in vitro. The influence of NKA may play a role in mechanisms by which tick saliva supports the transmission of tick-borne patogens.