Page 951 - Veterinary Immunology, 10th Edition

of dendritic cells. The salivary protein sialostatin-L2 inhibits
VetBooks.ir inflammasome activation. Tick saliva also inhibits the migration of

dendritic cells from inflamed skin to draining lymph nodes and
decreases the ability of these dendritic cells to present antigen to T

cells. Furthermore, the treated dendritic cells preferentially
stimulate Th2 responses. All these effects serve to facilitate the
prolonged attachment and feeding of ticks.
Because tick salivary proteins are antigenic, they would be

expected to induce immune responses that impair a tick's ability to
feed. Ticks, however, have evolved immunosuppressive and
antiinflammatory countermeasures that permit them to feed more
effectively. Tick saliva impairs macrophage function and

suppresses T cell responses to mitogens, as well as production of
IL-1β and the Th1 cytokines IFN-γ and IL-2. It suppresses NK cell
activity and macrophage nitric oxide production. Saliva from the
ticks Dermacentor andersoni and I. ricinus increases production of the

Th2 cytokines IL-4 and IL-10. A tick saliva immunosuppressor
binds specifically to T cell CD4 and blocks antigen-induced
signaling and T cell responses. Saliva from I. ricinus also inhibits
host B cell proliferation. Additionally, a serpin from I. ricinus

interferes with the IL-6 pathway and consequently inhibits Th17
cell differentiation. A salivary protein from I. scapularis inhibits the
proliferation of B cells exposed to the Osp proteins from the Lyme
disease bacterium Borrelia burgdorferi but has no effect on T cells. It

is abundantly clear that ticks have evolved many mechanisms to
prevent immunological attack while they are feeding.
Thus tick saliva contains components that suppress pain and itch,
hemostasis, inflammation, adaptive immunity, and wound healing.

Nevertheless, it has been observed that ticks on nonimmune
animals are larger than those on immune animals. Although the
nature of this resistance is unclear, it has been suggested that local
hypersensitivity reactions to tick saliva may restrict the blood flow

to the tick, reduce its food supply, and stunt its growth. It is
possible to immunize guinea pigs with tick homogenates and show
that ticks feeding on these animals have reduced fecundity.
Although vaccination against salivary antigens is unlikely to be
very effective in conferring effective immunity against blood

feeding arthropods, there is an alternative approach. Since many of

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