Page 644 - Veterinary Immunology, 10th Edition

synthesis. Activation of acetylcholine receptors on macrophages
VetBooks.ir inhibits production of IL-1 and TNF-α.

The production of antimicrobial proteins such as the defensins is
regulated by the autonomic nervous system, and stress reduces

cutaneous epithelial antimicrobial activity. This appears be a result
of increased glucocorticoid and acetylcholine production.
Both adrenergic and cholinergic stimulation increase
norepinephrine signaling, leading to NF-κB activation in

mononuclear cells. The sympathetic nervous system can alter the
Th1/Th2 balance through the β-adrenergic receptor. Stimulation of
sympathetic nerves enhances production of Th2 cytokines while
inhibiting production of Th1 cytokines. Norepinephrine suppresses

production of IL-6 and TNF-α.

Hypothalamic-Pituitary-Adrenal Cortical Axis

The adrenal cortex is stimulated by adrenocorticotropic hormone

(ACTH) from the pituitary under the influence of corticotrophin-
releasing hormone from the hypothalamus. As a result,
glucocorticoids are secreted and suppress T cell function by
blocking the NF-κB pathway. IL-1 and IL-6 act on both the
hypothalamus and the pituitary to increase ACTH production and

subsequent cortisol release.

Neuropeptides and Lymphocytes

Cells of the immune system have receptors for neuropeptides such

as the enkephalins and endorphins that thus can influence
lymphocyte activity. The generation of cytotoxic T cells is enhanced
by metenkephalin and β-endorphin, whereas α-endorphin
suppresses antibody formation and β-endorphin reverses this

suppressive effect. Other neuropeptides that influence the immune
system include ACTH, oxytocin, vasoactive intestinal peptide,
somatostatin, prolactin, and substance P.
Many neuropeptides such as vasoactive intestinal peptide and

neurokinin-1 (NK-1) have a similar structure to the antimicrobial
peptides so that they also have antimicrobial properties and may be
involved in host defense. For example NK-1, also known as

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