Targeted expression of human CD1d in transgenic mice reveals independent roles for thymocytes and thymic APCs in positive and negative selection of vα14i NKT cells

CD1d-dependent invariant V alpha 14 (V alpha 14i) NKT cells are innate T lymphocytes expressing a conserved semi-invariant TCR, consisting, in mice, of the invariant V alpha 14-J alpha 18 TCR alpha-chain paired mostly with V beta 8.2 and V beta 7. The cellular requirements for thymic positive and negative selection of Va14i NKT cells are only partially understood. Therefore, we generated transgenic mice expressing human CD1d (hCD1d) either on thymocytes, mainly CD4(+) CD8(+) double positive, or on APCs, the cells implicated in the selection of Va14i NKT cells. In the absence of the endogenous mouse CD1d (mCD1d), the expression of hCD1d on thymocytes, but not on APCs, was sufficient to select V alpha 14i NKT cells that proved functional when activated ex vivo with the Ag alpha-galactosyl ceramide. Va14i NKT cells selected by hCD1d on thymocytes, however, attained lower numbers than in control mice and expressed essentially V beta 8.2. The low number of V beta 8.2(+) V alpha 14i NKT cells selected by hCD1d on thymocytes was not reversed by the concomitant expression of mCD1d, which, instead, restored the development of V beta 7(+) V alpha 14i NKT cells. V beta 8.2(+), but not V beta 7(+), NKT cell development was impaired in mice expressing both hCD1d on APCs and mCD1d. Taken together, our data reveal that selective CD1d expression by thymocytes is sufficient for positive selection of functional V alpha 14i NKT cells and that both thymocytes and APCs may independently mediate negative selection.