Figure 3. m.3243A>G levels across bulk populations of peripheral immune cells.

Thirteen blood cell populations were separated by flow cytometry (n = 22); levels in platelets (n = 20) and granulocytes (n = 20) separated using density centrifugation from the same whole-blood sample are also shown. Each point in the flow cytometry-derived cell populations represents m.3243A>G levels in ∼1,000 cells isolated from a single individual. (A) m.3243A>G level is negatively correlated with age in all cell populations studied. Naïve/immature cell populations are represented in blue and memory/mature populations in red. Lines represent linear models with 95% confidence intervals; adjusted R² and P-values are shown. Linear mixed models of the effect of age and maturity on m.3243A>G levels including a term for the interaction of age with maturity show that m.3243A>G levels are lower in memory versus naïve CD4⁺ and CD8⁺ T cells (P = 0.0034, P = 0.0011) but not B cells (P = 0.7370) or mature versus immature NK cells (P = 0.5275). The slope is also significantly less steep for naïve CD4⁺ and CD8⁺ T cells (P = 0.0411 and P = 0.0223), but not for B or NK cells (P = 0.9898 and P = 0.6146). (B) All cell types studied within the T cell compartment have significantly reduced m.3243>G levels compared with CD34⁺ precursor cells, the most naïve blood cells investigated (linear mixed model accounting for patient as a fixed effect; CD4⁺ memory: β = −19.55, SE = 1.66, P < 0.0001; CD8⁺ memory: β = −18.82, SE = 1.666, P < 0.0001; CD4⁺ naïve: β = 12.82, SE = 1.66, P < 0.0001; CD8⁺ naïve: β = −12.18, SE = 1.66, P < 0.0001) and the memory B cells (β = −4.36, SE = 1.66, P = 0.0090) and granulocytes (β = −5.72, SE = 1.70, P = 0.0009). (C) Where available, m.3243A>G levels in whole blood are also shown (n = 12) (C) The same data are represented with lines connecting points from individual patients. Colours represent samples from the six patients taken forward for single-cell analysis. CD34⁺: precursor cells; immature NK: immature natural killer cells; mature NK: mature natural killer cells; CD11c⁺: myeloid dendritic cells; CD123⁺ pDCs: CD123⁺ plasmacytoid dendritic cells.