Figure 2.

FasL costimulation requires concomitant Ag-mediated TCR stimulation in naive CD8⁺ T cells, previously stimulated CD8⁺ T cells, and naive CD4⁺ T cells, but not in previously stimulated CD4⁺ T cell lines. [³H]dT uptake by B6.wt CD8⁺ splenocytes (A) and H-2^k-specific CTLs (C) pulsed on day 3 of coculture with H-2^k stimulators and either soluble HuIgG or FasIgG added on the indicated day. [³H]dT uptake by B6.lpr CD4⁺ splenocytes (B) and an H-2^bm12-specific B6.lpr CD4 line (D) pulsed on day 3 of coculture with H-2^bm12 stimulators and either soluble HuIgG or FasIgG added daily between days 0 and 3. Percentages were determined by normalizing the counts per minute of incorporated thymidine in cultures with soluble FasIgG to those in which soluble HuIgG was added on the given days. Experiments were repeated 1–3 times. The cpm incorporated in cultures with HuIgG ranged from 30,000-40,000 cpm in each of three experiments and data are averages of triplicate wells with error bars representing the SD of the mean.