An invariant T cell receptor alpha chain defines a novel TAP-independent major histocompatibility complex class Ib-restricted alpha/beta T cell subpopulation in mammals

We describe here a new subset of T cells, found in humans, mice, and cattle . These cells bear a canonical T cell receptor (TCR) alpha chain containing hAV7S2 and AJ33 in humans and the homologous AV19-AJ33 in mice and cattle with a CDR3 of constant length. These T cells are CD4(-)CD8(-) double-negat ive (DN) T cells in the three species and also CD8 alpha alpha in humans. I n humans, their frequency was similar to 1/10 in DN, 1/50 in CD8 alpha(+), and 1/6,000 in CD4(+) lymphocytes, and they display an activated/memory phe notype (CD45RA(lo)CD45RO(+)). They preferentially use hBV2S1 and hBV13 segm ents and have an oligoclonal V beta repertoire suggesting peripheral expans ions. These cells were present in major histocompatibility complex (MHC) cl ass II- and transporter associated with antigen processing (TAP)-deficient humans and mice and also in classical MHC class I- and CD1-deficient mice b ut were absent from beta 2-microglobulin-deficient mice, indicating their p robable selection by a nonclassical MHC class Ib molecule distinct from CD1 . The conservation between mammalian species, the abundance, and the unique selection pattern suggest an important role for cells using this novel can onical TCR or chain.