1. CD8 CD4 IgM B220 ThymusA. C.BM D. LN CD4 CD8 CD43 B220 IgM Spleen counts B220 IgD E. F. Kim et al._Fig. S1. PIDD +/+PIDD -/- Spleen CD44 CD25 Gated on CD4 - CD8 - subset B.

2. Kim et al._Fig. S2. Caspase-2 activity (RFU) Caspase-9 activity (RFU) No Tx Etoposide Etoposide Etoposide + VDVAD-CHO + DEVD-CHO No Tx Etoposide Etoposide + LEHD-CHO 2000 1500 1000 500 0 1800 1600 1400 1200 1000 800 600 400 200 0 Caspase-3 activity (RFU) No Tx γ-IR γ-IR + DEVD-CHO 50000 40000 30000 20000 10000 0

3. Supplementary Figure Legends: Fig. S1 Normal development of lymphocyte subsets in PIDD-deficient mice. Flow cytometric immunophenotyping of various immune sub-populations in (A)-(B) thymus, (C) bone-marrow (BM), (D) lymph-nodes (LN), and (E)-(F) spleen from PIDD+/+ and PIDD-/- mice. Numbers in each quadrant indicate the percentage of the cells. Results are representative of ≥3 independent experiments. Fig. S2 Absence of PIDD does not alter caspase activation in thymocytes. Caspase activities were quantified in the wild-type and PIDD-deficient thymocytes treated with either etoposide (for caspase-2 and -9 activities) or gamma-irradiation (for caspase-3 activity) with or without the following caspase inhibitors: VDVAD-CHO, caspase-2; DEVD-CHO, caspase- 3; LEHD-CHO, caspase-9. Caspase inhibitors were added immediately prior to the assay according to the manufacturer’s instruction). RFU=Relative fluorescent units.