Page 423 - Veterinary Immunology, 10th Edition

FIG. 14.21 γ/δ T cells may, depending on the species, act as
VetBooks.ir act as classic helper T cells with diverse TCRs of polyclonal origin.
innate immune cells with an invariant antigen receptor. Others may

In γ/δ-low species, there are two subsets of γ/δ cells. One subset

is engaged in innate immunity, has limited γ/δ receptor diversity,
and is mainly found in the skin and genital tract. The other subset is
engaged in adaptive immunity, has extensive receptor diversity,
and is found in secondary lymphoid organs and the digestive tract.

The innate γ/δ cells preferentially bind microbial PAMPs, especially
heat-shock proteins and phospholigands (carbohydrates or
nucleotides with a phosphate group). They also respond to the
MHC class Ib molecules, MIC-A and MIC-B, produced by stressed

cells, cancer cells, and virus-infected cells (Chapter 19). These innate
γ/δ T cells also respond to lipid antigens presented by CD1
molecules (see Chapter 19). When stimulated, they secrete IL-17
and IFN-γ. Like Th17 cells, innate γ/δ T cells are activated by IL-23.

In contrast, the adaptive subset of γ/δ T cells can be further
subdivided into helper and effector cells. These effector cells can
destroy cells infected with mycobacteria and some leukemic cells.
In γ/δ-high species, these T cells colonize the skin, mammary gland,

reproductive organs, tonsils, and the intestinal wall where they
form the major T cell population. They are polyclonal at birth, but
their diversity decreases with age. Between 50% and 99% of
ruminant blood γ/δ T cells express WC1 and are engaged in innate

immunity, whereas WC1-negative cells are regulatory cells. WC1 +
−
and WC1 cells have a different tissue distribution. WC1 −
+
predominate in the spleen and uterus. WC1 γ/δ T cells are found in
granulomas surrounding schistosomes and mycobacteria. In these

cases the initial T cell infiltration is dominated by γ/δ T cells and
this is followed by α/β T cells. A second wave of γ/δ T cells may
+
terminate the response. These WC1 cells secrete IL-12 and IFN-γ
and may promote a Th1 bias in the immune response. IFN-γ–

+
producing bovine γ/δ WC1 cells are the major population involved
in recall responses to Leptospira.
Bovine γ/δ T cells respond to microbial PAMPs by increasing the
expression of lymphotactin (XCL1), MIP-1β, TNF-α, and

granulocyte-macrophage colony-stimulating factor (GM-CSF). They
express TLR3, TLR9, mannose-binding lectin, and CD36. These γ/δ

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