Page 952 - Veterinary Immunology, 10th Edition

the arthropods of veterinary importance take the blood of their host
VetBooks.ir into their digestive tract, it follows that they will also take up

immunoglobulins, complement components, and cells. This
suggests that if an animal were immunized with internal antigens

from the tick, this could cause local damage. These internal antigens
have been called “hidden” or “concealed” antigens since under
normal circumstances the host would not usually encounter them.
Vaccines made against antigens from the intestine of the tick

Boophilus microplus can inhibit tick reproduction. Indeed, a
recombinant tick vaccine based on such a recombinant antigen,
Bm86, is available in Australia and Central America. The antibodies
produced bind to the brush border of tick intestinal cells, inhibit

endocytosis, and prevent the tick from engorging fully. Thus the
digestive processes are impaired, and the tick experiences
starvation, loss of fecundity, and weakness, and may disengage
from its host. As a result, the number of ticks on vaccinated animals

is reduced. Experimental multicomponent tick vaccines show even
more encouraging results.

Hypoderma Infestation

Unlike the arthropods described previously, the larvae of the

warble flies (Hypoderma bovis and Hypoderma lineatum) actually
migrate through body tissues. These larvae must survive or evade
the host's xenograft response. In fact, the first instar larvae of these

flies do not trigger significant inflammation and are also
immunosuppressive. Hypodermin A, the protease secreted by these
larvae, can inhibit responses to mitogens and reduce IL-2
production, probably by destroying cell surface receptors.
Vaccination with a cloned Hypoderma protein has effectively

protected cattle against subsequent infestations.
Immune defenses also play a role in preventing invasion by other
skin-penetrating arthropods. Body strike results when the larvae of

the fly Lucilia cuprina attack the skin of a sheep. Sheep can be bred
for low and high resistance to body strike. The resistant sheep have
greater numbers of IgE-positive B cells in their skin than do
susceptible sheep. Resistant sheep also mount a greater
inflammatory response and produce more fluid exudate when

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