PROMINENCE OF GAMMA-DELTA T-CELLS IN THE RUMINANT IMMUNE-SYSTEM

The lymphoid systems of sheep and cattle contain a large number of gamma-delta T cells, in striking contrast to the lymphoid systems of humans and mice. In neonatal animals particularly, these cells comprise the predominant fraction of T cells in the blood. Here Wayne Hein and Charles Mackay discuss what is currently known about the ontogeny, phenotype, tissue distribution and function of gamma-delta T cells in ruminants. There are a number of interesting molecular features that characterize ruminant-gamma-delta T cells, but these do not entirely explain the high frequency of use of the gamma-delta T-cell receptor in these animals. Studies on sheep, cattle or other animals that preferentially use gamma-delta T cells should provide insights into the biological significance of the existence of two distinct forms of the T-cell receptor.