Fig. 1

Peripheral blood monocyte populations change with age and sex. (A) The flow cytometry data gating strategy for peripheral whole-blood immunophenotyping of classical (CD14⁺CD16⁻), intermediate (CD14⁺CD16⁺⁺) and non-classical (CD14⁻CD16⁺⁺) monocyte populations. Both age and sex altered monocyte prevalence (as a proportion of total CD45⁺ leukocytes): total monocytes (B), classical monocytes (C), non-classical monocytes (D). Absolute monocyte numbers were not significantly affected by chronological age in the whole population (males and females) but showed a differential influence of biological sex. Total monocyte (E), classical monocyte (F), and non-classical monocyte (G) numbers increased in females with age. There were no sex differences in the surface expression of mobilization markers CC-chemokine receptor 2 (CCR2) and CX₃CR₁, though both increased with age in the whole population (H, I). In contrast, there was no age-associated change in the surface expression of monocyte activation markers CD13 and CD64 (data not shown), but expression was higher in females, inclusive of all ages (J, K). Monocyte surface receptor expression as mean fluorescence intensity (MFI). Data is shown as a dot for each participant. Subjects are color coded according to their biological sex (Male – black; female – grey). Statistical significance was assessed by simple linear regression (A-I) and Students’ t test (J,K)