NKT cells affect cytokine production of CD4 and CD8 Tcon. Balb/c recipients (H-2^d) were transplanted with TCD-BM and either 5.0 × 10⁵ Tcons or 5.0 × 10⁵ Tcons + 2.5 × 10⁴ NKT cells. Cells were then reisolated at the indicated days after transplantation from lymph nodes, liver, or spleen (spln). FACS analysis of intracellular cytokines was performed with donor-specific and congenic markers to separate NKT cells from Tcons. Shown are representative FACS data showing the median of 3 independent experiments. (A) Cytokine expression of IFN-γ by CD4 or CD8 donor-type Tcons shows the addition of NKT cells to cause a more rapid decline in the percentage of IFN-γ–expressing Tcons. The observed decreases in IFN-γ expression in the presence of NKT cells were very significant (P < .0001) based on an unpaired t test between mean fluorescence intensities of plots shown. (B) Cytokine expression of TNF-α by CD4 or CD8 donor-type Tcons shows that the addition of NKT cells results in a more rapid decline in the percentage of TNF-α–expressing Tcons. The decreases in TNF-α expression in the presence of NKT cells were very significant (P < .0001) based on an unpaired t test between mean fluorescence intensities of plots shown. (C) Cytokine expression of IL-4 by CD4 cells was not significantly altered by the addition of NKT cells, with no apparent trends of increased or decreased expression of IL-4 indicated between experiments.