Page 710 - Veterinary Immunology, 10th Edition

nearby enterocytes to secrete protective nitric oxide.
VetBooks.ir percent of IELs in humans, 50% in mice, and up to 90% in
There are major species differences in the properties of IELs. Five

ruminants carry γ/δ TCR. A high proportion of the IELs are CD8 +

(85% in humans, 77% in pigs, 24% in sheep). These CD8 molecules
are α/α homodimers, in contrast to the CD8 α/β heterodimers
found on conventional α/β T cells. IELs tend to use unusual TRGV
and TRDV genes to form the TCR antigen-binding site. These genes

are not expressed in other lymphoid organs, suggesting that the
intraepithelial T cells are specialized for epithelial surveillance. IELs
are MHC class II positive and may act as antigen-presenting cells.
They regulate B cell IgA responses. Some have natural killer (NK)

cell activity, whereas others are cytotoxic T cells that may attack
parasites within the intestinal lumen. They also play a role in the
repair of damaged epithelia.
Some of the γ/δ T cells in the intestine can produce IL-17. There

are two different sets of these cells. ILC3s that produce IL-17
spontaneously and Th17 cells that produce it following antigen
exposure and are presumably proinflammatory (Chapter 21).

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