Caspase-1–dependent secretion of IL-18 is derived from hosts.

WT or caspase-1–deficient BALB/c (Casp1^−/−) mice were lethally irradiated and underwent transplantation with WT or caspase-1–deficient B6/129 spleen cells (5 × 10⁷). At day 5, serum was sampled and IL-18 levels were determined. Serum IL-18 in irradiated WT or caspase-1–deficient BALB/c mice having transplantation with BALB/c spleen cells at day 5 was not detectable. NS indicates not significant. Data represent the mean ± SD of 5 mice in each experimental group. Similar results were obtained in 3 independent experiments.