l-Tryptophan–Kynurenine Pathway Metabolites Regulate Type I IFNs of Acute Viral Myocarditis in Mice

Abstract

The activity of IDO that catalyzes the degradation of tryptophan (Trp) into kynurenine (Kyn) increases after diseases caused by different infectious agents. Previously, we demonstrated that IDO has an important immunomodulatory function in immune-related diseases. However, the pathophysiological role of IDO following acute viral infection is not fully understood. To investigate the role of IDO in the l-Trp–Kyn pathway during acute viral myocarditis, mice were infected with encephalomyocarditis virus, which induces acute myocarditis. We used IDO-deficient (IDO−/−) mice and mice treated with 1-methyl-d,l-Trp (1-MT), an inhibitor of IDO, to study the importance of Trp–Kyn pathway metabolites. Postinfection with encephalomyocarditis virus infection, the serum levels of Kyn increased, whereas those of Trp decreased, and IDO activity increased in the spleen and heart. The survival rate of IDO−/− or 1-MT–treated mice was significantly greater than that of IDO+/+ mice. Indeed, the viral load was suppressed in the IDO−/− or 1-MT–treated mice. Furthermore, the levels of type I IFNs in IDO−/− mice and IDO−/− bone marrow-transplanted IDO+/+ mice were significantly higher than those in IDO+/+ mice, and treatment of IDO−/− mice with Kyn metabolites eliminated the effects of IDO−/− on the improved survival rates. These results suggest that IDO has an important role in acute viral myocarditis. Specifically, IDO increases the accumulation of Kyn pathway metabolites, which suppress type I IFNs production and enhance viral replication. We concluded that inhibition of the Trp–Kyn pathway ameliorates acute viral myocarditis.

Blockade of Indoleamine 2,3-Dioxygenase Reduces Mortality from Peritonitis and Sepsis in Mice by Regulating Functions of CD11b+Peritoneal Cells

“…For blockade of Ido, mice were administered 1-MT (5 mg/ml) in their drinking water starting from 3 days before or from just after CLP, and on average, each mouse consumed 3.5 ml/day. L-Kyn was administered as described previously (19,32). Briefly, mice were intraperitoneally injected with L-Kyn (20 mg/kg of body weight; Sigma-Aldrich) 24 h before CLP.…”

“…L-Kyn was measured using high-performance liquid chromatography (HPLC) with a spectrophotometric detector (UV-8000; Tosoh, Tokyo, Japan) as described previously (19,32).…”

“…Subsequently, the cells were incubated with primary antibodies against Ido and CD11b (Santa Cruz Biotechnology, Santa Cruz, CA, USA) for 1 h at 4°C. The anti-Ido polyclonal antibody was generated by the peptide H-CMKPSKKKPTDGDKS-OH in rabbits as described previously (19,32). After washing with 0.1% Tween 20 containing PBS, the cells were incubated with the secondary antibodies fluorescein isothiocyanate (FITC)-conjugated anti-mouse IgG and rhodamine-conjugated anti-rabbit IgG (DakoCytomation, Carpinteria, CA, USA).…”

“…BMT. Bone marrow (BM) transplantation (BMT) was performed on 5-week-old male mice as described previously (32). The recipient mice (Ido ϩ/ϩ and Ido Ϫ/Ϫ mice) were irradiated in fractionated doses (5 Gy twice with a 4-hour interval) and reconstituted with whole BM cells by injection (5 ϫ 10 6 BM cells from Ido ϩ/ϩ or Ido Ϫ/Ϫ donor mice) via the tail vein.…”

IDO1 Plays an Immunosuppressive Role in 2,4,6-Trinitrobenzene Sulfate–Induced Colitis in Mice

“…;GFP-Tg mice (F2). Bone marrow transplantation was performed as described previously (17). All recipients were given 500 U/ml gentamicin sulfate (Invitrogen, Grand Island, NY) in the drinking water starting 2 d before and continuing for 26 d after transplantation.…”