The mice were monitored for fungal growth and histopathology in the target organs (the lungs in aspergillosis and the colon in candidiasis), as were the parameters of immune resistance and tolerance, i.e., the patterns of inflammatory/anti-inflammatory cytokine production and the combined activity of the aryl hydrocarbon receptor (AhR)/indoleamine 2,3-dioxygenase (IDO) pathway, known to contribute to immune tolerance in infection [17]. The gene discussed is IDO1; the disease is aspergillosis.