Cutting edge:: Selective expression of inhibitory or activating killer cell Ig-like receptors in circulating CD4+ T lymphocytes

Apart from NK cells, TCR gamma delta and CD8(+) T cells, killer cell Ig-like receptor (KIR) expression was described on a minor subset of CD4(+) T cells. However, their functions remain to be elucidated in this latter lymphocyte population. We demonstrated that KIR2DL2/L3 (CD158b) and KIR2DS2 (CD158j) transcripts were synthesized by sorted CD4+ CD158b/j(+) T cells obtained from healthy individuals. In contrast, we observed that only the inhibitory or activating receptor was expressed at the cell surface according to the donor tested. In CDI-58b-expressing cells, KIR triggering leads to an inhibition of the CD3-induced cell proliferation and Erk activation, and the receptor exhibits an activation-dependent tyrosine phosphorylation and association with the Src homology 2-containing phosphatase 1. In CD158j-positive cells, KIR-engagement results in an enhanced CD3-mediated cell growth and Erk phosphorylation. Our results suggested that, in contrast to NK cells, the functions of KIR in CD4(+) T lymphocytes might derive from a selective expression of their activating or inhibiting forms.