A1AT decreases serum HS levels and improves the outcome of GVHD after allo-HSCT. (A) Serum HS concentrations were determined by ELISA at the indicated time points after allo-HSCT (B10.D2→BALB/c; 1 × 10⁷ B10.D2 TCD-BM and 5 × 10⁶ B10.D2 LC) treated with A1AT (2 mg) or PBS every 3 days by intraperitoneal injection, starting 1 day before transplantation; n = 3 per data point (*P < .05). Survival (B) and GVHD clinical score (C) of allo-BM only (n = 5) or allo-BM + LC treated with A1AT (n = 8) or PBS (n = 5). Data are from 1 of 2 independent experiments with identical results. GVHD pathology score (D) and representative H&E histology (E) of BALB/c recipients of B10.D2 (allo) TCD-BM + LC treated with PBS or with A1AT (n = 6 per group; bar denotes 100 μm (*P = .05). The micrographs were taken from H&E sections (200× magnification) using the 20× PlanApochromatic objective with an Olympus Vanox-AHBS-3 microscope. The camera used is Olympus DP-70 with its own acquisition software. (F) Survival of lethally irradiated C57BL/6 recipients of 1 × 10⁷ C3H.SW TCD-BM (allo-BM) and 5 × 10⁶ C3H.SW LC administered A1AT (n = 10) or PBS (n = 9). (G) Improvement in GVHD survival by A1AT is dependent on host TLR4 expression. Survival of BALB/c recipients of allo-BM + LC from B10.D2 donors (n = 11) and TLR4^−/− BALB/c recipients of allo-BM + LC from B10.D2 donors administered A1AT (n = 8) or PBS (n = 14) every 3 days by intraperitoneal injection, starting 1 day before transplantation.