Comparative metabolic analyses of classical vs nonclassical monocytes. (A) Basal mitochondrial respiratory activity (Routine), complex IV activity (COX), and residual oxygen consumption (ROX) were determined by high-resolution respirometry in both classical and nonclassical monocyte populations. Routine and COX activity were corrected for ROX respiration, because this oxygen consumption is not related to the mitochondrial respiratory system. All parameters were increased and the elevation of routine respiration was significant (P ≤ .05, Wilcoxon matched-pairs test) in nonclassical monocytes. Shown are arithmetic means and standard errors of the mean (n = 6 for routine respiration, n = 5 for COX and ROX). (B) The activity of CS, a mitochondrial matrix marker enzyme, is increased in nonclassical monocytes. Shown are arithmetic means and standard error of the mean (n = 5). The difference was not significant in the Wilcoxon matched-pairs test. (C) Mitochondrial content, determined by MitoTracker staining and analyzed by flow cytometry, was not different between the 2 subpopulations. Shown is 1 representative experiment of n = 3. FITC, fluorescein isothiocyanate.