Close Phenotypic and Functional Similarities Between Human and Murine αβ T Cells Expressing Invariant TCR α-Chains

Several studies have demonstrated the existence of a murine NK1.1⁺ αβ T cell subset expressing Vα14⁺ TCR α-chains with highly conserved invariant junctional sequences and able to secrete Th2 cytokines when exposed to CD1⁺ stimulator cells. In humans, α/β T cells carrying invariant Vα24⁺ TCR α-chains highly homologous to those expressed by murine NK1.1 cells have been recently described. Here we show that these cells (referred to as Vα24^inv T cells) and murine NK1.1⁺ αβ T cells resemble each other in several ways. First, like their murine counterparts, T cells expressing high levels of Vα24^inv TCRs can be either CD4^-CD8^- double negative (DN) or CD4⁺, but they never express heterodimeric CD8 molecules. Second, most Vα24^inv T cells are brightly stained by NKRP1-specific mAb but not by mAb directed against other type II transmembrane proteins of the NK complex. Third, DN and particularly CD4⁺ Vα24^inv T cells are greatly enriched for IL-4 producers. The concomitant expression of highly conserved TCRs of a particular set of NK markers and of Th2 cytokines in human and murine αβ T cells suggests a coordinate acquisition of these phenotypic and functional properties. Furthermore, the relatively high frequency of human Vα24^inv T cells, which are presently shown to represent on average 1/500 PBL, and the high interindividual variations of the size of this cell subset under physiologic conditions go for a major role played by αβ T cells carrying invariant TCR in a large array of immune responses.