Type I (sometimes known as invariant) NKT cells express a semi-invariant TCRα chain (Vα 14Jα18 in mice Vα24Jα18 in humans) that pairs with a biased pool of TCRβ chains through which they recognise self and foreign glycolipids presented in complex with CD1d 1. Natural Killer T (NKT) and Mucosal-Associated Invariant T (MAIT) cells are two distinct classes of unconventional αβ T cells that recognise non-peptide antigens in complex with MHC class-I-like molecules. Accordingly, we have provided an extensive analysis of the in situ localisation of NKT and MAIT cells and suggest differences between the intra-organ location of these two cell types. In contrast to NKT cells, MAIT cells were more closely associated with the B cell zone and red pulp of the spleen. MAIT cells were clearly detectable in Vα19 TCR transgenic mice and were rare but detectable in lymphoid tissue of non-transgenic mice.

In spleen and lymph nodes, NKT cells were mainly localised within T cell zones, although following in vivo activation with the potent NKT-cell ligand α-GalCer, they expanded throughout the spleen. Within the thymus, NKT cells were concentrated in the medullary side of the corticomedullary junction. Here, using CD1d and MR1 tetramer staining techniques, we describe the precise location of NKT and MAIT cells in lymphoid and peripheral organs. These cells play important roles in health and disease in many organs, but their precise intra-organ location is not well established. Natural Killer T (NKT) cells and Mucosal-Associated Invariant T (MAIT) cells are innate-like T cells that express semi-invariant αβ T cell receptors (TCRs) through which they recognise CD1d and MR1 molecules, respectively, in complex with specific ligands.

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