Page 939 - Veterinary Immunology, 10th Edition

positive feedback loop generating the other Th2 cytokines and IL-
VetBooks.ir 25. The IL-4 activates STAT6, which upregulates GATA3 that

causes differentiation into Th2 cells and suppresses Th1 responses.
IL-6 acts with TGF-β to induce Th17 responses. IL-13 repairs

epithelia, enhances mucus production, and with IL-9 recruits and
activates mucosal mast cells. Both IL-4 and IL-13 activate
enterocytes, smooth muscle cells, and macrophages. Increased
enterocyte proliferation and turnover may cause worm

disengagement. These cytokines also increase intestinal
permeability and fluid secretion. The Th2 cytokines stimulate
Paneth cells and the consequent increase in defensins may damage
helminths. These cytokines also stimulate goblet cells to produce a

resistin-like molecule that interferes with worm feeding. Mucins
and other goblet cell products may also promote worm expulsion.
While embedded in the intestinal and abomasal mucosa, worms
secrete multiple antigenic proteins (Fig. 28.9) and these will

stimulate production of both IgA and IgE. IgA is associated with
resistance to Teladorsagia circumcincta, affecting both worm size and
fecundity. IgE responses are probably more important than IgA
since they play a key role in controlling adult worms on mucosal

surfaces. This is most evident in the “self-cure” reaction in sheep
infected with gastrointestinal nematodes, particularly Haemonchus
contortus.

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