In the groups vulnerable to developing severe COVID-19, such as elderly populations and individuals with the comorbidities Diabetes Mellitus II and Cerebrovascular Disease, the kynurenine in this pathway is highly activated [196,212], which could lead to an increase of pro-inflammatory cytokines and constitutive AHR activation, which is related to the reduced antiviral response by INF-1 [213,214]. The gene discussed is AHR; the disease is COVID-19.