Characterization of an immunosuppressant protein from Dermacentor andersoni (Acari: Ixodidae) salivary glands.

A 36-kDa soluble protein was found in the salivary glands of female Dermacentor andersoni (Stiles) ticks that suppressed the in vitro proliferative response of murine splenocytes to concanavalin A (Con A). Incubating the purified protein with splenocytes reduced the incorporation of thymidine into the DNA of proliferating T-lymphocytes by more than 90% compared with cells exposed to Con A and buffer alone. The N-terminal amino acid sequence of the immunosuppressant protein was determined to be NH2-Leu-His-Lys-Ala(Asp)-Lys-Ile-Val-Lys-Leu-Thr -Glu-Glu-Ala -Arg-Lys-Tyr-Val-Gly-Arg-Xxx-Xxx-Thr-Thr-Ala-Leu-Gly-. Although the sequence exhibited a modest degree of similarity with a segment of immunoglobulin-binding protein found in several species of mammals, the mode of action of the immunosuppressant protein is unknown. This protein may play an important role in suppressing the host's acquisition of resistance to ticks.