The expression of Indoleamine 2, 3-dioxygenase (IDO) is reduced in granulomas from BCG vaccinated cattle compared to granulomas from unvaccinated controls after experimental challenge with Mycobacterium bovis.

Bovine tuberculosis (bTB), mainly caused by Mycobacterium bovis (M. bovis), is a major economic disease of livestock worldwide. Vaccination is considered as a potentially sustainable adjunct to the current control strategy. Cattle vaccination with the live attenuated M. bovis bacillus Calmette-Guerin (BCG) confers variable protection; the reasons for this variability are not understood.