Page 385 - Veterinary Immunology, 10th Edition

drops to 30% by 1 year and to 5% by 5 years. The genes encoding
VetBooks.ir these γ/δ T cells show much less diversity than the genes encoding

their α/β T cells.

Pigs

Pig leukocytes express nine unique surface proteins (SWC1 to
SWC9). SWC1 is expressed on resting T cells, monocytes, and
granulocytes but not on B cells. It is homologous to CD52. SWC2 is

homologous to CD 27 and is found on T and NK cells. SWC3 is
found on monocytes and macrophages. SWC9 is expressed only by
mature macrophages. Pigs are a γ/δ–high species. In young pigs, up
to 66% of blood T cells are γ/δ positive, but this drops to 25% to
50% in adults. Pigs have two subpopulations of γ/δ T cells. One is

−
+
CD2 and the other is CD2 and has not been identified in other
species. Some pig γ/δ T cells can function as antigen-presenting
cells using MHC class II molecules. Up to 60% of T cells in pig
+
+
blood are double positive (CD4 , CD8 ). The rest are predominantly
−
−
+
double negative (CD4 , CD8 ). Some CD4 T cells also express
CD8α/α homodimers and are cytotoxic.

Dogs and Cats

In dogs, CD4 is expressed on neutrophils and macrophages but not
on monocytes, whereas in cats, CD4 is found on only a subset of T
cells and their precursors.

385