IL-1β plays a protective role by suppressing T cells. (A) Kaplan-Meier survival curve of Balb/c-recipient GVHD mice receiving MDSC-IL13s (M13) from WT or IL-1β–deficient donors. Whole T cells (WTCs) vs M13, P < .0001; WTCs vs IL-1β KO, P = .0434; M13 vs IL-1β KO, P = .0027. Data represent 2 independent pooled experiments, n = 20 per group. (B) Cultured MDSC-IL13s from WT or IL-1R KO donors were plated in a suppression assay at a 1:3 or 1:9 ratio as indicated with CFSE-labeled naïve responder IL-1R KO T cells and T cell–depleted stimulators (0.5×) from IL-1R KO donors with 0.25 µg/mL of anti-CD3ε. Histograms represent loss of CFSE fluorescence from cell division 3 days after coculture and are coded for clarity with text. Summary data for the 1:3 (C) and 1:9 ratios, representing 3 independent cultures per group, representative of 3 independent experiments. *P < .05, **P < .01. ns, not significant.