The complementarity determining region 2 of BV8S2 (V beta 8.2) contributes to antigen recognition by rat invariant NKT cell TCR

Invariant NKT cells (iNKT cells) are characterized by a semi-invariant TCR comprising an invariant α-chain paired with β-chains with limited BV gene usage which are specific for complexes of CD1d and glycolipid Ags like α-galactosylceramide (α-GalCer). iNKT cells can be visualized with α-GalCer-loaded CD1d tetramers, and the binding of mouse CD1d tetramers to mouse as well as to human iNKT cells suggests a high degree of conservation in recognition of glycolipid Ags between species. Surprisingly, mouse CD1d tetramers failed to stain a discrete cell population among F344/Crl rat liver lymphocytes, although comprised iNKT cells are indicated by IL-4 and IFN-γ secretion after α-GalCer stimulation. The arising hypothesis that rat iNKT TCR recognizes α-GalCer only if presented by syngeneic CD1d was then tested with the help of newly generated rat and mouse iNKT TCR-transduced cell lines. Cells expressing mouse iNKT TCR reacted to α-GalCer presented by rat or mouse CD1d and efficiently bound α-GalCer-loaded mouse CD1d tetramers. In contrast, cells expressing rat iNKT TCR responded only to α-GalCer presented by syngeneic CD1d and bound mouse CD1d tetramers only poorly or not at all. Finally, CD1d-dependent α-GalCer reactivity and binding of mouse CD1d tetramers was tested for cells expressing iNKT TCR comprising either rat or mouse AV14 (Vα14) α-chains and wild-type or mutated BV8S2 (Vβ8.2) β-chains. The results confirmed the need of syngeneic CD1d as restriction element for rat iNKT TCR and identified the CDR2 of BV8S2 as an essential site for ligand recognition by iNKT TCR.