Abstract # 3136 Diurnal variation in immune markers among caregivers of children newly diagnosed with cancer

Many human PNI studies examine associations between psychosocial factors and immune markers assessed at a single time point, without consideration of time of day (TOD). However, immune parameters show circadian variation, and stress exposure may affect these biological rhythms. We examined diurnal variation in immune markers among 120 mothers sampled at 1,6, and 12 months following their child’s cancer diagnosis. Using linear mixed models, we assessed the impact of time of blood draw on monocyte and white blood cell(WBC) concentration, peripheral levels of interleukin(IL)-6, LPS-stimulated levels of IL-6 (whole blood), and glucocorticoid receptor(GR) sensitivity (LPS, hydrocortisone suppression). Controlling for age, education, race, BMI, child’s cancer treatment intensity, and repeated measures, we found significant increases in WBC concentration (B = 1669.3cells/mL/h, p = .003), and LPS-stimulated levels of IL-6 (B = 1074.0 pg/mL/h, p = .018) over the course of the day. These findings replicate prior work showing inverse associations between daily cortisol levels and immune parameters. In contrast, we found no association between TOD and monocyte concentration, peripheral levels of IL-6, or GR sensitivity (p’s > .05). These latter results conflict with findings in healthy individuals, suggesting that in the context of stress, some immune parameters may show disruption in circadian rhythm. Possible mechanisms include disruption of environmental cues that entrain circadian rhythms, such as sleep or eating patterns. Future studies should consider the impact of TOD on blood sampling, particularly for individuals under high stress conditions.