Primary structure and variation of the T-cell receptor δ-chain from a marsupial, Macropus eugenii

Although γδ T-cells form only a small portion of circulating T-cells in mice and humans, they are more frequent in many other types of mammals and this has lead to speculation regarding their roles and the evolutionary significance of their relative abundance. Moreover, whilst clear homologues of four types of T-cell receptor (TCR) chains (α, β, δ and γ) have been identified in vertebrates as distantly related as eutherian mammals and cartilaginous fish, there are still many gaps in our knowledge of these TCR components from various taxa. Such knowledge would further illuminate the evolution and function of these receptors and of γδ T-cells. Here, we report the molecular cloning of a TCR-δ chain cDNA from the tammar wallaby (Macropus eugenii) which represents the first component of the γδ TCR to be characterised from a marsupial. A PCR-based survey of variable (V) segment usage in tammar wallaby mammary-associated lymph node indicated that, although γδ T-cells may be sparse in this type of tissue, this species has at least three subfamilies of V genes that have been broadly conserved across vertebrate evolution. Two V subfamilies found in the tammar wallaby were relatively similar and may have diverged more recently, an event that probably occurred at some point in the marsupial lineage.