-in the peripheral blood of patients with moderate to severe COVID-19, low concentrations of BHB irrespective of calorie intake and blood glucose levels-BHB resulted in improved mitochondrial function, and fatty acid and amino acid oxidation; reduced glycolysis in CD4 + T lymphocytes-cultures of human TH1 CD4 + lymphocytes with BHB showed an increase in the number of CD4+ cells and IFNy production, and a decrease in PD-1 (programmed death receptor 1) expression. This evidence concerns the gene CD4 and COVID-19.