Page 950 - Veterinary Immunology, 10th Edition

the T cells of dogs with demodicosis are washed free of serum, they
VetBooks.ir regain their ability to respond to mitogens. Serum from these

animals is also able to suppress T cell proliferation in normal
animals.

Flea-Bite Dermatitis

Biting fleas secrete saliva into the skin wound. Some of the
components of flea saliva are of low molecular weight and act as

haptens after binding to dermal collagen As a result, a local type IV
hypersensitivity reaction characterized by a mononuclear cell
infiltration occurs. In some sensitized animals, this type IV reaction
is gradually replaced over a period of months by a type I reaction,
and the mononuclear cell infiltration gradually changes to an

eosinophil infiltration. The immune response mounted by flea-
allergic animals is protective. Thus fleas produce fewer eggs on
flea-allergic cats than on flea-naïve cats. Flea-allergic cats also

appear to remove more fleas by grooming than do flea-naïve
animals. Experimental vaccines containing the major antigens from
the cat flea midgut have been able to reduce flea populations on
dogs, and the female fleas recovered from these immunized
animals produced significantly fewer eggs. This suggests that

vaccination may eventually be effective in controlling flea
populations.

Tick Infestation

Ticks are unique among arthropods in the way they attach and feed
from their hosts for several days. This provides time for immune
responses to occur and for ticks to employ countermeasures. For
example, their saliva contains kininases that destroy bradykinin

and histamine-binding proteins, thus reducing pain and itch. The
saliva of the tick Ixodes scapularis contains a protein that regulates
the alternative complement pathway. It displaces properdin and
enhances the degradation of C3bBb convertase. Tick saliva also

contains an inhibitor of the complement lectin pathway. As a result,
host scratching and grooming responses are minimized.
The saliva of Ixodes ricinus impairs the antigen-presenting abilities

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