Intraindividual Variability and the Effect of Acute Illness on Immune Senescence Markers

Objectives: To determine the intraindividual variability and effect of acute illness on two markers of immune senescence. Design: Cohort study with repeated measures. Setting: Clinical research center and emergency department at two academic medical centers. Participants: Seventy‐three subjects aged 65 and older enrolled in three groups: chronic underlying conditions but no acute illness, acutely ill with infection (community‐acquired pneumonia), and acutely ill without infection. Measurements: CD16 density on polymorphonuclear neutrophils (PMNs) and the proportion of CD8+ T cells that express CD28 determined twice in the nonacutely ill group and three times (Days 0, 30, and 60) in the acute illness groups. Results: In the nonacutely ill group, PMN CD16 density demonstrated wide intraindividual variation, but there was a strong correlation for repeated measures of the percentage of CD8+ T cells expressing CD28 (correlation coefficient (r)=0.77, P