Abstract
Mitochondrial function studies in human leukocytes have mainly focused on peripheral blood mononuclear cells (PBMCs), with the assumption that the immunometabolic properties of different immune cells have a negligible effect on PBMCs. Using a high-throughput mitochondrial phenotyping platform to quantify multiple mitochondrial features among both PBMCs and immunologically-defined immune cell subtypes from the same individuals, we show how mitochondrial activity in PBMCs is confounded by both cell type distributions and contaminating platelets. Then, applying this cell-specific approach in women and men spanning 4 decades of life, we find that mitochondria exhibit specific age- and sex-related differences, including an age-related elevation in mitochondrial DNA copy number (mtDNAcn), which are masked or blunted in PBMCs. Our purified cell subtypes data also define in humans the variation in mtDNAcn, mitochondrial content (citrate synthase), and respiratory chain enzymatic activities among neutrophils, monocytes, B and T lymphocyte subtypes. Moreover, we validate these cell type differences and define the natural intra-individual variation in mitochondrial function using an intensive repeated-measures study in a single individual, revealing substantial natural variation over time among cell subtypes and PBMCs. Finally, we introduce multivariate mitochondrial phenotypes – mitotypes – that distinguish lymphoid from myeloid cell types, naïve-to-memory lymphocyte states, and moderately differ between women and men, which we propose as potential cell-specific biomarkers for future studies. Together, these findings identify dynamic cell-type specific variation in mitochondrial biology in circulating human leukocytes, providing foundational knowledge to develop interpretable blood-based assays of mitochondrial health.
Competing Interest Statement
The authors have declared no competing interest.
