Sulfatide-reactive type II NKT cells can suppress tumor immunity, but their characterization has been hampered by lack of widespread availability of flow-cytometry markers.  Our previous observation that sulfatide treatment reduced the protective effect of a-GalCer treatment in a CT26 lung metastasis model suggested that there are sulfatide-reactive regulatory type II NKT cells in the lung, which is a major site of both primary tumors and metastases. We have used stable sulfatide-CD1d tetramers to characterize these cells in the lung. This analysis revealed unique characteristics. In contrast to type I NKT cells and some other non-sulfatide-reactive type II NKT cells reported previously, sulfatide-reactive lung type II NKT cells develop in a PLZF-independent fashion. They express higher levels of TCRb and CD3 than type I or liver type II NKT cells. They are predominantly CD4⁺, but include a substantial number of double-negative and CD8 single-positive cells, unlike murine type I NKT cells. Their Vb repertoire is diverse, more like that of conventional T cells. A sizable number express some myeloid markers including CD11b and Ly6C. Over a third of the Ly6C positive subpopulation express the mast cell marker c-kit, which is not expressed normally in T cells outside the thymus. Morphologically, however, they look like conventional lymphocytes with slightly more cytoplasm containing azurophilic granules.  They also express constitutive levels of granzyme A, unlike conventional T or type I NKT cells.  When stimulated in vivo with sulfatide, they upregulate Ki-67 and also increase granzyme A expression.  Unlike type I NKT cells, distinct populations of type II NKT cells make IFNg or IL-13, not both. In summary, we have identified a unique subpopulation of lung type II NKT cells with a unique phenotype and function.