Fig. 1.

Conventional and unconventional T cells. T cells can be broadly grouped as conventional or unconventional based on their restriction molecules, while both groups of T cells can either be “innate-like” or “adaptive” depending on their innate-ness. Conventional T cells are MHC-restricted T cells that express TCRs composed of highly variable αβ chains, while unconventional T cells are non-MHC restricted T cells that recognise non-peptide, non-polymorphic antigen-presenting molecules and express either αβ or γδ TCRs. Within unconventional T cells, γδ T cells that express the Vδ2 chain are mostly Vγ9+Vδ2+ T cells which express the innate-like T cell transcription factor promyelocytic leukaemia zinc finger (PLZF) and are “innate-like” compared to γδ T cells that express the Vδ1 chain, which have been shown to have more adaptive biology. MAIT cells and iNKT cells also express PLZF, have a semi-invariant TCR and are considered “innate-like”. Within conventional T cells, memory CD4+ and CD8+ T cells are adaptive, while the recently discovered T_MIC (MHC II-restricted, innate-like, and commensal reactive T cells) [16] are “innate-like”, expressing PLZF and with the ability to be activated in a TCR-independent manner, despite being MHC class II-restricted. Created with Biorender.com.