Abstract
Natural killer T (NKT) cells are αβ T cell receptor (TCR) expressing innate-like T cells that display natural killer (NK) cell markers. Based on TCR characteristics, they are divided into two groups restricted to the MHC class I-like molecule CD1d. Type I NKT cells, most extensively studied, are identified by a semi-invariant Vα14-Jα18 (mouse, Vα24-Jα18 in humans) TCR reactive to the prototypic ligand α-galactosylceramide presented on CD1d. In contrast, type II NKT cells display diverse TCR reacting to different CD1d-presented ligands. There are no reagents that identify all type II NKT cells, limiting their exploration. Here, we searched for novel type II NKT cells by comparing Jα18-/- MHCII-/- mice that harbour type II but not type I NKT cells, and CD1d-/- MHCII-/- mice, lacking all NKT cells. We identified significantly larger populations of CD4+ and CD4- CD8- (double negative, DN) TCRβ+ cells expressing NKG2D or NKG2A/C/E in Jα18-/- MHCII-/- mice compared with CD1d-/- MHCII-/- mice, suggesting that 30%-50% of these cells were type II NKT cells. They expressed CD122, NK1.1, CXCR3 and intermediate/low levels of CD45RB. Further, the CD4+ subset was CD69+ , while the DN cells were CD49b+ and CD62L+ . Both subsets expressed the NKT cell-associated promyelocytic leukaemia zinc finger (PLZF) transcription factor and Tbet, while fewer cells expressed RORγt. NKG2D+ CD4+ and DN populations were producers of IFN-γ, but rarely IL-4 and IL-17. Taken together, we identify a novel subset of primary CD4+ and DN type II NKT cells that expresses NKG2 receptors have typical NKT cell phenotypes and a TH1-like cytokine production.