Page 1020 - Veterinary Immunology, 10th Edition

production and reduce the recruitment of inflammatory cells. In
VetBooks.ir humans, this reduces mast cell and eosinophil numbers in the lung,

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as well as the infiltration of CD4 T cells and eosinophils in the skin.
It induces a shift in the dominant helper cell response from Th2 to

Th1 (Fig. 30.13). For example, the IFN-γ/IL-4 ratio is low in atopic
dogs, indicating a Th2 cytokine profile. After immunotherapy, the
ratio rises, IFN-γ levels increase, and the balance shifts toward a
Th1 response. This IFN-γ reduces the effects of Th2 cells on IgE

antibody synthesis and shifts allergen-specific immunoglobulin
production from IgE to IgG. Immunotherapy may also induce
dendritic cell production of IL-12 and IL-18 and promote Th1
responses. It also stimulates Tregs to produce IL-10, inhibiting IgE

production, mast cell activation, and histamine and leukotriene
release.

FIG. 30.13 The principles of allergen-specific immunotherapy.
Increasing doses of allergen promote a Th1 response, while at the
same time reducing the Th2 response and regulating antibody
production.

In immunotherapy, small amounts of dilute aqueous solutions of
antigen are administered. The first injections contain very little
allergen. Over a number of weeks, the dose is gradually increased.
If an animal's allergy is of the seasonal type, the course of injections

should be timed to reach completion just before the anticipated
antigen exposure. It has been estimated that up to 80% of dogs have
a good to excellent response to this procedure. This includes clinical
improvement and a reduction in the amount of medication

required. It may take several months before the benefits of
immunotherapy become apparent. Cats may respond even better

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