Peritoneal macrophages from old mice exhibit quantifiable signs of aging. (a) Aged peritoneal macrophages had reduced oxygen consumption rate (OCR) both at baseline (N = 9/group; 2-tailed, unpaired Welch's t-test) and in response to oligomycin (N = 11–12/group; 2-tailed, unpaired t-test) and significantly reduced ATP-linked respiration (b; N = 9/group; 2-tailed, unpaired Welch's t-test). (c) Lipopolysaccharide (LPS)-treated aged peritoneal macrophages also had impaired mitochondrial bioenergetics at baseline (N = 8–12/group; 2-tailed, unpaired Welch's t-test) and significantly reduced ATP-linked respiration (d; N = 6–9/group; 2-tailed, unpaired t-test) compared to LPS-treated young peritoneal macrophages. (e) Aged peritoneal macrophages had increased mRNA expression of the senescence marker p16INK4a (N = 10/group; 2-tailed, unpaired t-test). Open circles depict individual data points; horizontal lines depict mean ± SEM (a-e) (* P < .05; ** P < .01; *** P < .001; **** P < .0001).