SALIVARY-GLAND EXTRACTS OF PARTIALLY FED DERMACENTOR-RETICULATUS TICKS DECREASE NATURAL-KILLER-CELL ACTIVITY IN-VITRO

The salivary glands and saliva of ticks (Arachnida, Acari, Ixodida) pl ay a vital role in blood feeding, including manipulation of the host's immune response to tick infestation. Furthermore, a diverse number of tick-borne pathogens are transmitted to vertebrate hosts via tick sal iva. A factor synthesized in the salivary glands of feeding ticks pote ntiates the transmission of certain tick-borne viruses. We show that s alivary gland extracts (SGE) derived from Dermacentor reticulatus fema le ticks fed for 6 days on laboratory mice (SGED6) induced a decrease in the natural killer (NK) activity of effector cells obtained from 16 healthy blood donors. The decreased activity ranged from 14 to 69% of NK activity observed with the respective untreated effector cells. Su ch a decrease was not observed after treatment of effector cells with SGE from unfed ticks. Ten-fold dilution of SGED6 significantly reduced the capacity to decrease NK activity and a further IO-fold dilution a lmost eliminated the effect. After addition of IFN-alpha 2, the SGED6- induced decrease in NK activity was restored to activity levels approa ching those of untreated cells. The apparent reversibility of the inhi bition indicates that the effect of SGED6 on NK activity was not due t o cytotoxicity. The results demonstrate the presence of st factor(s) i n the salivary gland products of feeding D. reticulatus female ticks t hat influences human NK activity in vitro. These data suggest a possib le mechanism by which tick SGE potentiates the transmission of some ti ck-borne viruses through suppression of NK activity.