Factors that are critical for NK T cell–mediated protection. (A) WT or Jα281−/− mice were injected subcutaneously (hind flank) with 105 MCA-1 cells. Subgroups of Jα281−/− mice were simultaneously treated with either PBS, or 3 × 105 NKT cells, as part of a liver lymphocyte population, from either WT, IFN-γ−/−, or pfp−/− donor mice via intravenous adoptive transfer. Significant difference from the PBS-treated Jα281−/− group was determined by a Fisher's exact test. *P ≤ 0.05; **P ≤ 0.01. (B) Groups of (i) Jα281−/−, (ii) CD1d−/−, (iii) IFN-γ−/−, (iv) pfp−/−, (v) Jα281−/− mice treated with depleting anti-asGM1 Ab, (vi) Jα281−/− mice treated with depleting anti-CD8, and (vii) RAG-1−/− mice, were injected subcutaneously (hind flank) with 105 MCA-1 cells. One-half of each group of mice were simultaneously injected with 2.5 × 105 sorted WT NK T cells via intravenous adoptive transfer, while the other half were injected intravenously with 2% NMS.PBS. Sorted NK T cells were always at least 97% pure as determined by FACS®. (B) i, ii, and iii represent pooled data from two independent experiments, iv represents data from one of these experiments, v, vi, and vii represent data from one independent experiment with three to six mice per group per experiment. Significant difference from the PBS-treated control group of each experiment was determined using a Mann-Whitney U test. *P ≤ 0.05; **P ≤ 0.01.