The biology and evolution of the unconventional γμ T cell in non-eutherian mammals.

Abstract

Abstract There are three lineages of T cells in mammals, αβ, γδ and γμ T cells, classified by the composition of their T cell receptors (TCR). γμ T cells are present only in marsupials and monotremes. The γμTCR has a number of unique features, most distinctly is the three extracellular-domain TCRμ chain. In this study we investigate the evolution of the TCRμ genes and characteristics of γμ T cells in different species. γμ T cells appear to have tissue specific residency. In adult opossums, Monodelphis domestica, they are restricted to the spleen, liver, throughout the gut, and mesenteric lymph nodes. By comparison, in the Tasmanian devil, Sarcophilus harrisii, there was also tissue specific residency in liver, spleen, bone marrow, and skin. In opossums and Tasmanian devils, the TRMlocus is organized as discrete, tandem clusters, and there is evidence of lineage specific cluster duplication. In a monotreme, the platypus, TRMis less organized, although there is evidence of ancestral cluster-like patterns. Our results support conserved patterns of tissue specific residency of the unconventional γμ T cell in marsupials and help to reconstruct the evolution of this unique T cell type. NSF IOS-2103367 DGE-1939267