Inhibition of cell division of naive CD4⁺ T cells cocultured with tolerized CD4⁺ cells. The addition of tolerized cells inhibits cell division of naive CD4⁺ T cells in vitro. CFSE-labeled naive B6 CD45.2 CD4⁺ T cells were cultured with bm12 stimulators with or without the addition of tolerized B6 CD45.1 CD4⁺ cells at a ratio of 4 naive cells to 1 tolerized cell. On day 6, CD45.2 CD4⁺ cells were identified (Figure 2A) and analyzed for CFSE dilution by flow cytometry (Figure 2B). 17.5% of naive cells cultured alone and 3.2% of naive cells cocultured with tolerized cells had undergone 2 or more cell divisions. Gates for each number of cell divisions were calculated based on comparison with undivided control cells (Table 1). Data are representative of 2 replicate experiments with similar results.