T cell receptor signalling in γδ cell development: strength isn't everything.

γδ cells have been conserved across ∼450 million years of evolution, from which they share the distinction, alongside αβ T cells and B cells, of forming antigen receptors by somatic gene recombination. However, much about these cells remains unclear. Indeed, although γδ cells display 'innate-like' characteristics exemplified by rapid tissue-localised responses to stress-associated stimuli, their huge capacity for T cell receptor (TCR)γδ diversity also suggests 'adaptive-like' potential. Clarity requires a better understanding of TCRγδ itself, not only through identification of TCR ligands, but also by correlating thymic TCRγδ signalling with commitment to γδ effector fates. Here, we propose that thymic TCRγδ-ligand engagement versus ligand-independent signalling differentially imprints innate-like versus adaptive-like characteristics on developing γδ cells, which fundamentally dictate their peripheral effector properties.