Therapeutic effects of L-Kyn on IPS. (A-B) Lethally irradiated B6.WT mice were injected with BALB/c.Ifng^−/− T cells (1 × 10⁶) and BALB/c.WT TCD BM cells. Lungs were harvested on day 7 (n = 5 per group). (A) Levels of Ahr expression were measured by real-time polymerase chain reaction (PCR). (B) Immunohistochemical staining of AHR. Representative images (×200) are shown. (C-F) GVHD was induced as described in panels A and B. Recipients were intraperitoneally injected with L-Kyn (100 mg/kg) with or without CH-223191 (10 mg/kg) each day from day 3 through day 8. Lungs were harvested on day 9 (C) or 14 (D-F). (C) Cyp1b1 expression was measured by real-time PCR (n = 5 per group). (D) Representative images of hematoxylin and eosin staining (×200; left) and histopathologic scoring (right; n = 5 per group). (E-F) Levels of cytokine messenger RNA (mRNA) were measured by real-time PCR (n = 5 per group). Results are representative of at least 3 independent experiments with similar results. Data represent mean ± standard error of the mean. Nonparametric Mann-Whitney U test (A) and 1-way analysis of variance (C-F) were performed. *P < .05, **P < .01, ***P < .001.