Mitochondrial phenotypes in purified human immune cell subtypes and cell mixtures

Using a high-throughput mitochondrial phenotyping platform to quantify multiple mitochondrial features among molecularly defined immune cell subtypes, we quantify the natural variation in mitochondrial DNA copy number (mtDNAcn), citrate synthase, and respiratory chain enzymatic activities in human neutrophils, monocytes, B cells, and naive and memory T lymphocyte subtypes. In mixed peripheral blood mononuclear cells (PBMCs) from the same individuals, we show to what extent mitochondrial measures are confounded by both cell type distributions and contaminating platelets. Cell subtype-specific measures among women and men spanning four decades of life indicate potential age- and sex-related differences, including an age-related elevation in mtDNAcn, which are masked or blunted in mixed PBMCs. Finally, a proof-of-concept, repeated-measures study in a single individual validates cell type differences and also reveals week-to-week changes in mitochondrial activities. Larger studies are required to validate and mechanistically extend these findings. These mitochondrial phenotyping data build upon established immunometabolic differences among leukocyte subpopulations, and provide foundational quantitative knowledge to develop interpretable blood-based assays of mitochondrial health.

Automated summary

Using a high-throughput mitochondrial phenotyping platform, this study quantified multiple mitochondrial features among different immune cell subtypes in humans, revealing natural variations in mtDNA copy number, citrate synthase, and respiratory chain enzymatic activities in various cell types. The results showed that cell type distributions and contaminating platelets can confound mitochondrial measures. Age- and sex-related differences in mitochondrial features were observed, with age-related elevation in mtDNAcn often masked in mixed PBMCs. A proof-of-concept study in a single individual also demonstrated cell type differences and week-to-week changes in mitochondrial activities. Validation and mechanistic studies are needed to further explore these findings.