T cell activation increases CD38 expression, which increases catalytic activity on T cells, and in their homing sites. NAD removal by CD38 inactivates sirtuins, which decreases oxidative phosphorylation via the inhibition of PGC-1 and the activation of HIF-1 alfa. This blocks the entrance to mitochondria of pyruvate and products of lipid beta oxidation. NAD depletion additionally decreases the use of lipid beta oxidation products by mitochondria, via inactivation of mitochondrial Sirt3. Inactivation of Sirt 4 increases mitochondrial production of reactive oxygen species (ROS). Activation also increases CD4 T cell expression of the glucose transporter Glut 1, the entrance of glucose, and an increase in glycolysis. Pyruvate produced by glycolysis is not transported to mitochondria, but reduced to lactate, which is transported outside the cell. Warburg effect, entailing glycolysis-dominated metabolism, is thus enforced.