A Natural Killer T (NKT) Cell Developmental Pathway Involving a Thymus-dependent NK1.1−CD4+ CD1d-dependent Precursor Stage

Abstract

The development of CD1d-dependent natural killer T (NKT) cells is poorly understood. We have used both CD1d/α-galactosylceramide (CD1d/αGC) tetramers and anti-NK1.1 to investigate NKT cell development in vitro and in vivo. Confirming the thymus-dependence of these cells, we show that CD1d/αGC tetramer-binding NKT cells, including NK1.1+ and NK1.1− subsets, develop in fetal thymus organ culture (FTOC) and are completely absent in nude mice. Ontogenically, CD1d/αGC tetramer-binding NKT cells first appear in the thymus, at day 5 after birth, as CD4+CD8−NK1.1−cells. NK1.1+ NKT cells, including CD4+ and CD4−CD8− subsets, appeared at days 7–8 but remained a minor subset until at least 3 wk of age. Using intrathymic transfer experiments, CD4+NK1.1− NKT cells gave rise to NK1.1+ NKT cells (including CD4+ and CD4− subsets), but not vice-versa. This maturation step was not required for NKT cells to migrate to other tissues, as NK1.1− NKT cells were detected in liver and spleen as early as day 8 after birth, and the majority of NKT cells among recent thymic emigrants (RTE) were NK1.1−. Further elucidation of this NKT cell developmental pathway should prove to be invaluable for studying the mechanisms that regulate the development of these cells.

Limited correlation between human thymus and blood NKT cell content revealed by an ontogeny study of paired tissue samples

“…Consistent with its importance as a marker of NKT maturity in mice [14][15][16], CD161 was expressed by a significantly higher proportion of NKT cells in blood compared to thymus (n=24; p<0.001) (Fig. 7).…”

“…However, studies in mice have shown that NKT cells pass through an immature NK1.1 -(CD161 -) stage of development and that most NKT cells are exported from the thymus at this immature stage, presumably to continue their maturation in the periphery [14][15][16].…”

CD1d-restricted iNKT cells, the ‘Swiss-Army knife’ of the immune system

“…NFκB, T-bet, Ets1, Runx1, RORγ, Itk, Rlk, AP-1) (see Ref [4] for reviews), and co-stimulatory molecules such as CD28 and ICOS [11]. Most iNKT cells leave the thymus in an immature stage (as defined by the absence of expression of NK receptors such as NK1.1) and fulfill their terminal maturation in the periphery [12][13][14]. However, a sizeable fraction of these NK1.1 − iNKT cells in the peripheral organs do not acquire expression of NK markers and in fact represent mature cells that are functionally distinct from their NK1.1 + thymic counterpart [15λ] (see below).…”

Differential alteration of lipid antigen presentation to NKT cells due to imbalances in lipid metabolism

“…Va14i NKT cells, which can be either CD4 + or CD4 -CD8 -double negative (DN), are a thymus-dependent population derived from CD4 + CD8 + double-positive (DP) thymocytes [7][8][9][10][11]. Different maturation stages of developing thymic Va14i NKT cells have been described, characterized by the sequential acquisition of CD44 and NK1.1 in C57BL/6 mice [12][13][14]. Unlike conventional MHC-dependent T cells, Va14i NKT cells are not positively selected by thymic epithelial cells but rather by hematopoietic cells [2,[15][16][17][18], in particular by CD1d-expressing DP cortical thymocytes [19,20], which alone are sufficient for positive selection of Va14i NKT cells [21,22].…”