โ Scribed by Dale I. Godfrey; Kirsten J.L. Hammond; Lynn D. Poulton; Mark J. Smyth; Alan G. Baxter
No coin nor oath required. For personal study only.
KT cells are a population of T cells that share some characteristics with natural killer (NK) cells (reviewed in Refs 1-3). The key features characteristic of NKT cells include heavily biased T-cell receptor (TCR) gene usage, CD1d restriction and high levels of cytokine production, particularly interleukin 4 (IL-4) and interferon โฅ (IFN-โฅ) (Fig. 1). In mice, these cells are commonly defined as NK1.1 ฯฉ โฃโคTCR ฯฉ . However, as cells bearing these markers are phenotypically and functionally heterogeneous, it is appropriate to compare the different subsets of cells encompassed within this population. Most of the studies covered in this review relate to NKT cells in mice, unless otherwise specified.
Although the term NKT was only recently applied, these cells were first described in 1987. Most of the earlier studies in mice focussed on thymic โฃโคTCR ฯฉ T cells that were CD4 and CD8 double negative (โฃโคDN) and highly biased toward Vโค8-2 expression. A major subset of these cells was found to express NK1.1, previously associated with NK cells, and to have the potential to secrete high levels of IL-4, IFN-โฅ and tumor necrosis factor (TNF). A population of NK1.1 ฯฉ CD4 ฯฉ T cells was also identified with similar characteristics 1-3 . Subsequent reports showed that both populations predominantly express TCR Vโฃ14Jโฃ281 and that their development was dependent on the MHC class I-like, โค 2microglobulin-associated molecule, CD1d. These findings strongly suggested that NK1.1 ฯฉ โฃโคDN and NK1.1 ฯฉ CD4 ฯฉ T cells were part of the same lineage 1-3 . Thus, in recent years NKT cells are usually identified by the coexpression of the โฃโคTCR and NK1.1, as shown in Fig. 2.
Several recent studies in mice have demonstrated the potential danger of oversimplifying our classification of NKT cells [4][5][6][7][8] . These studies have shown that CD4 ฯฉ , DN and CD8 ฯฉ NK1.1 ฯฉ T cells are
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