Aging associates with elevated TNF-⍺ plasma levels and platelet hyperreactivity in mice and humans. (A) TNF-⍺ plasma levels from heathy young (8-12 weeks) and old (>72 weeks) C57BL/6J mice (n = 6-8; mean plus or minus SEM). Hematological profile of (B) platelets, (C) hemoglobin (Hgb), and (D) leukocytes from healthy young and old C57BL/6J mice (n = 8-20 mice per group; mean plus or minus SEM). (E) Platelet activation analysis by flow cytometry of washed platelets from young (8-12 weeks) and old (>72 weeks) mice stimulated with thrombin (0.1 IU/mL) as determined by activation of the ⍺_IIbβ₃ integrin (n > 3 per experiment with 3-5 biological replicates). Mann-Whitney test. (F) Platelet phosphatidylserine (PS) exposure 5 minutes after activation with thrombin (0.1 IU/mL) of washed platelets from young (8-12 weeks) and old (>72 weeks) C57BL/6J mice (n = 6; mean plus or minus SEM) using bovine fluorescein isothiocyanate (FITC)-lactadherin. Student t test. (G) Assessment of platelet adhesion and clot formation over collagen-coated slides under physiological flow conditions (650 s⁻¹) of reconstituted whole blood. Normal pooled murine plasma and erythrocytes were mixed with washed platelets from either young (8-12 weeks) and old (>72 weeks) mice at the same concentration. Representative TEM of clots formed over collagen-coated slides by TEM (n = 5-6; mean plus or minus SEM). Mann-Whitney test. (H) Activation profile of the ⍺_IIbβ₃ integrin in human washed platelets from younger (mean age, 35.0 ± 10.1 years; n = 25) and older (mean, 79.5 ± 8.8 years; n = 25) healthy volunteers. Mann-Whitney test. *P < .05; **P < .01; and ***P < .001. max, maximum; NS, not significant.