Differential surface receptor expressions of aging platelets in circulation. Isotype control–corrected expression of receptors on age-tracked platelets, relative to global population expression (represented as 0 on y-axis for normalization), as measured by flow cytometry in samples obtained from individual mice on day 1 (green) and 5 (cyan) after labeling. Between days 1 and 5 of age, significant decreases in expression of MHC-I (A), GPVI (B), and CD31/PECAM-1 (C), but no difference in expression of CD49a/integrin α2 (D) or CD41/integrin α2b (E) was detected, whereas significant increase in CD9 expression (F) was detected. ∗∗P < .01, ∗∗∗P < .001 as analyzed by paired t test.