IL-2:anti-IL-2 mAb complexes were described previously26 (link),27 (link). Briefly, 1.5 μg IL-2 recombinant protein (eBioscience) was incubated with 7.5 μg of functional grade anti-IL-2 mAb (clone JES6-1, eBioscience) for 30 min at 37 °C. Complexes were added directly to thymic slices (10 μl/slice) daily over the course of the experiment. Mouse MOG 35–55 and chicken OVA 323–339 peptides were purchased from Anaspec. Peptide was overlaid on thymic slices for 10–30 min after thymocyte migration into the slice.