Research has proven that tryptophan metabolism plays a key role in regulating the immune response of the body against C. albicans. Tryptophan could activate the microbial-dependent AhR/IL-22 axis to inhibit fungal growth and infection on the mucosal surface and thus prevent abnormal immune stimulation by C. albicans (Romani et al., 2008). The gene discussed is IL22; the disease is infection.