Intracellular pH links energy metabolism to lymphocyte death and proliferation

The role of intracellular pH (pHi) of lymphocytes in the control of the magnitude of immune response is unknown. The central question addressed in this report is whether energy metabolism affects pHi, which in turn regulates the death and proliferation of the lymphocytes and hence the magnitude of the immune response. To this end, we studied lymphocytes in the in vitro model of anti-CD3 activation and the in vivo mouse model of ovalbumin sensitization and challenge. We found that low pHi induces apoptosis of proliferating lymphocytes, whereas high pHi is conducive to their survival. In the in vivo model, treating the mice with the metabolic regulators dichloroacetate or C75 that increase the influx of carbons derived from pyruvate and fatty acid to the TCA cycle, respectively, lowered pHi. Treatments with the metabolic regulators CB-839 or GSK2837808A that inhibit glutaminolysis and aerobic glycolysis, respectively, also lowered pHi. Proliferation powered by high mitochondrial membrane potentials (MMPs) in lymphocytes of low but not high pHi was accompanied by apoptosis. After antigenic challenge, lymphocytes of high pHi increased and assumed a positive relation between pHi and MMPs, while lymphocytes of low pHi and with an inverse relation between pHi and MMPs diminished. These changes were largely dependent on glutaminolysis and aerobic glycolysis. It is therefore concluded that glutaminolysis and aerobic glycolysis are important for counterbalancing the acidic effects of pyruvate and fatty acid energy metabolism to promote a favorable pHi environment for lymphocyte survival and the progression of the immune response.