Features of mitochondrial state in CD4<sup>+</sup>Т lymphocyte subsets

Peripheral blood CD4+T lymphocytes are heterogenous, including naive, central memory, effector memory, and terminally differentiated effector cells. Each subset performs different functions and possesses unique metabolic properties. Mitochondria are vital organelles of CD4+T lymphocytes, playing critical roles in metabolism, energy and active oxygen species production, cellular respiration, proliferation, differentiation, and apoptosis. The use of mitochondrial-selective fluorescent dyes in combination with labeled monoclonal antibodies is a relatively accessible and simple way to study a range of mitochondrial parameters in CD4+T cells of varying maturity by flow cytometry. The aim of this study was to investigate mitochondrial indices in different CD4+T lymphocyte subsets. We obtained mononuclear cells from peripheral blood of nine relatively healthy volunteers. By flow cytometry using commercial fluorescent dyes MitoTracker Green FM and MitoTracker Deep Red FM, we determined the mass and membrane potential of mitochondria in the total pool of CD4+T lymphocytes and in their subsets: naive (CD45R0-CCR7+), central memory (CD45R0+CCR7+), effector memory (CD45R0+CCR7-), and terminally differentiated effectors (CD45R0-CCR7-). We show that in healthy individuals, central and effector memory CD4+T lymphocytes compared to naive cells have increased mitochondrial mass and membrane potential. The mass of organelles in functionally different memory CD4+T cell subsets vary significantly: it is lower in central memory lymphocytes than in effector memory cells. Nevertheless, two subsets have similar mitochondrial membrane potential. Terminally differentiated effectors differ from other CD4+T lymphocyte subsets in unique characteristics of mitochondria: despite high mass, they have a reduced membrane potential. This feature may be linked to cells being prepared for programmed cell death during the terminal differentiation stage.