Characterization of histamine binding proteins from Ixodes persulcatus and their assessment as candidates for anti-tick vaccine

Tick feeding activities and transmission of pathogens cause great losses not only in the livestock industry, but also in public health. Particularly, Ixodes ticks are known as vectors of Borrelia burgdorferi sensu lato which cause Lyme borreliosis. Since ticks play important roles as vectors of various pathogens, suppression of their population is the most effective way to control the diseases which they transmit. At present, ticks can be effectively controlled by the use of acaricides, which have many disadvantages. Hence, it is necessary to develop alternative tick-control methods such as an immunological way, which is currently considered as a major sustainable and practical method. Previously, it was reported that immunosuppressive factor from Ixodes persulcatus, termed Salp15, promoted the infection of B. burgdorferi by its adhesion to a bacterial surface protein, OspC. In addition, RNA interference-mediated repression of Salp15 in I. persulcatus drastically reduced the capacity of B. burgdorferi to infect mice. Thus, the objective of this study was to obtain immunosuppressive factors from I. persulcatus, which is a vector for Lyme borreliosis and tick-borne encephalitis in East Asia. Total of 198 cDNAs were cloned from a cDNA library constructed from salivary glands of fed female ticks. Four cDNA clones, termed as IpHBP 1, 2, 3 and 4, have sequences similar to the Histamine binding protein genes expressed in other lxodes ticks. RT-PCR analysis showed that IpHBPs were expressed specifically in the salivary glands of fed females. Western blot analysis showed that IpHBP 2, 3, and 4 were ‘exposed’ antigens. Although recombinant IpHBPs (rIpHBPs) expressed in Escherichia coli did not show the binding activities to histamine, vaccination of mice with the rIpHBPs delayed engorgement of ticks and reduced their engorged body weight. These results suggested that IpHBPs suppressed the inflammation during infestation of ticks and could be potential candidate antigens for anti-tick vaccine.