Treg proliferation was diminished in the presence of IL-12, resulting in an effective change in ratio of the two cell types within a single culture (Fig. 1C, D) . However, it is also possible that IL-12 augmented Treg cell death or induced conversion of Tregs to Tconvs, which would have the same effect. To address the role of apoptosis, we measured AnnexinV expression on Tconvs and Tregs in lymph nodes cultures. IL-12 treatment did not increase the percentage of either AnnexinV + Tregs or Tconvs in the cultures, demonstrating that there was no preferential Treg death (Fig. 6) .