Metabolic features of naïve and memory CD4<sup>+</sup>T cells in quiescence and during proliferation

Background. Memory CD4+ T cells proliferation is the basis for accelerated secondary immune response. The characteristics of memory CD4+ T cells providing their faster division compared to naive CD4+ T lymphocytes are poorly understood. T cells proliferative ability is determined by their metabolism. The metabolic features of proliferating memory CD4+ T cells remain elusive. The aim. To compare the metabolic features of naive and memory CD4+ T cells in quiescence and during proliferation. Methods. Peripheral blood mononuclear cells were analyzed using flow cytometry. Dividing cells were identified by CD71 expression. Cellular glucose and fatty acid uptake was assessed using fluorescent glucose (2-NBDG) and palmitate (BODIPY-FL-C16) analogs, respectively. Glutamine transporter expression was analyzed by staining the cells with anti-ASCT2 antibodies. Mitochondrial mass and membrane potential were measured using MitoTracker Green and MitoTracker Orange, respectively. Results. Quiescent memory CD4+ T cells exhibited elevated levels of glucose and palmitate uptake when compared to naive CD4 + T lymphocytes (p < 0.001). Both subsets had increased substrate consumption when proceeding to proliferation (p < 0.001). When dividing, naive CD4+ T cells consumed more glucose and palmitate than memory CD4+ T cell (p < 0.001). Proliferation caused an increase in mitochondrial mass in naive (p < 0.001) and memory CD4+ T lymphocytes (p < 0.05). In memory CD4+ T cells, unlike naive CD4+ T lymphocytes, an increase in mitochondrial mass wasn’t accompanied by an increase in membrane potential. Conclusion. In memory CD4 + T cells, compared to naive CD4+ T lymphocytes, the metabolic change induced by proliferation is moderate and affects the mitochondrial activity to a lesser extent. Lower bioenergetic expenses of memory CD4+ T cells can contribute to their rapid proliferation during secondary immune response.