Background & Aims CD1d-restricted natural killer (NK) T cells are a subset of immunoregulatory T cells that comprise type I (express the semi-invariant T-cell receptor [TCR] and can be detected using the α-GalCer/CD1d tetramer) and type II (express diverse TCRs and cannot be directly identified). Studies in mouse models of inflammatory bowel disease revealed a complex role for type I NKT cells in the development of colitis. Type II NKT cells have been associated with intestinal inflammation in patients with ulcerative colitis. Method To investigate whether dysregulation of type II NKT cells, caused by increased expression of CD1d, can contribute to colitis, we generated transgenic mice that express high levels of CD1d and a TCR from an autoreactive, type II NKT cell (CD1dTg/24αβTg mice). Results CD1dTg/24αβTg mice had reduced numbers of 24αβ T cells, compared with 24αβTg mice, indicating that negative selection increases among type II NKT cells engaged by abundant self-antigen. The residual 24αβ T cells in CD1dTg/24αβTg mice had an altered surface phenotype and acquired a cytokine profile distinct from that of equivalent cells in 24αβTg mice. Interestingly, CD1dTg/24αβTg mice spontaneously developed colitis; adoptive transfer experiments confirmed that type II NKT cells that develop in the context of increased CD1d expression are pathogenic. Conclusions Aberrant type II NKT cell responses directly contribute to intestinal inflammation in mice, indicating the importance of CD1d expression levels in the development and regulation of type II NKT cells.

CD1d is an MHC class Ib molecule that is specialized to present lipid antigens to NKT cells. Two subsets of NKT cells have been identified: type I NKT cells express an invariant TCR α chain while type II NKT cells express a more diverse TCR repertoire. Recent studies have shown that a specific pattern of CD1d expression is required for proper development and function of type I NKT cells. However, little is known about the regulation and selection of type II NKT cells as there is no method for direct detection of these cells. To address whether changes in CD1d expression patterns can regulate the function of type II NKT cells, we have generated a double transgenic mouse model, CD1dTg/24αβTg, that expresses high levels of CD1d as well as a TCR isolated from the type II NKT cell clone 24αβ. Total numbers of 24αβ T cells are significantly reduced in CD1dTg/24αβTg mice, suggesting that type II NKT cells undergo negative selection when engaged by abundant self-antigen. The remaining 24αβ T cells exhibit an altered surface phenotype and produce increased levels of inflammatory cytokines compared to equivalent cells that develop in a wild type B6 background. Interestingly, CD1dTg/24αβTg mice spontaneously develop inflammatory bowel disease (IBD) characterized by extensive colonic inflammation. Our studies highlight the importance of CD1d expression levels in the regulation of type II NKT cells and reveal a potential role for type II NKT cells in the pathogenesis of IBD.