Gamma Delta T cells
Gamma Delta T cells (γδ T cells) represent a very small subset of T cells that possess a distinct T cell receptor (TCR) on their surfaces. A majority of T cells have a TCR composed of two glycoprotein chains called α- and β- TCR chains. However, in γδ T cells, the TCR is made up of one γ-chain and one δ-chain. This group of T cells is much less common in humans and mice (about 2% of total T cells) and are found mostly in the gut mucosa, within a population of lymphocytes known as intraepithelial lymphocytes. In rabbits, sheep, and chickens, the number of γδ T cells can be as high as 60% of total T cells. The antigenic molecules that activate γδ T cells are still widely unknown. However, γδ T cells are not MHC-restricted and seem to be able to recognize whole proteins rather than requiring peptides to be presented by MHC molecules on APCs.