Figure 1.

Positive selection and apoptosis of double-positive thymocytes in response to variant and agonist peptides. (A) Fetal thymic lobes from day 16 F5/TAP1° embryos were cultured for 10 days with the indicated concentrations of the various peptides. Thymocytes were harvested and stained with anti-CD4, anti-CD8, and anti-Vβ11 mAbs. The bar chart shows the absolute number of Vβ11^hi CD8⁺ thymocytes produced in each case. Each bar represents the average number from a pool of four individual FTOCs. Positive selection using NP68 and NP34 was seen in three and seven independent experiments, respectively. NP4Q failed to cause any significant positive selection in two independent experiments. (B) Fetal thymic lobes from F5/Rag-1° day 15 embryos were cultured for 4 days in medium alone and then transferred to medium containing different concentrations of NP68, NP34, NP4Q, or GAG peptides. Thymocytes were harvested after 12 hr and stained with anti-CD4 and anti-CD8 mAbs and with 7AAD. The graph depicts the percentage of double-positive thymocytes containing subdiploid DNA. The mean and standard deviations of three fetal thymic lobes are shown for each point.