Page 949 - Veterinary Immunology, 10th Edition

basophils are destroyed by antibasophil serum, resistance to biting
VetBooks.ir arthropods is reduced. The third type of response to arthropod

saliva is a Th2 response, leading to eosinophil infiltration, IgE
production, and type I hypersensitivity. This response may induce

severe local inflammation, leading to urticaria, pain, or pruritus.
Each of these three types of response may modify the skin in such a
way that the feeding of the offending arthropod is impaired and the
animal becomes a less attractive source of food. Unfortunately,

natural selection and evolution ensure that the biting arthropod is
well able to withstand such responses. (These hypersensitivities are
discussed further in Chapter 30.)

Demodectic Mange

The mange mites Demodex folliculorum, D. canis, and D. injai are
common in mammalian hair follicles and sebaceous glands.
Normally present in low numbers, generalized demodicosis results

from mite overgrowth. Under normal circumstances, an innate
immune response to mite chitin and an adaptive response to mite
antigens maintain mite populations at a low level. The development
of generalized demodicosis results from defects in host immunity
and has a strong genetic component. The inflammatory reaction

around mites and mite fragments contains mononuclear cells with a
few plasma cells. The infiltrating lymphocytes are predominantly
+
CD8 T cells. Type II granuloma formation may occasionally occur.
The presence of cytotoxic T cells suggests that this is a type IV
hypersensitivity reaction. Dogs do, however, make antibodies to
mite proteins. The absence of eosinophils and edema in the lesion
suggests that type I hypersensitivity is relatively unimportant. It is
of interest to note that immunosuppressive agents such as

antilymphocyte serum, azathioprine, or prolonged steroid therapy
predispose animals to the development of demodectic mange.
Animals with generalized demodicosis have normal neutrophil

function and respond normally to vaccines or other foreign
proteins. Nevertheless, their T cell response to mitogens such as
phytohemagglutinin and concanavalin A is depressed. This is a
progressive suppression, and it tends to increase in severe cases. It
has been suggested that it reflects T cell “exhaustion.” If, however,

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