The effects of exercise and diurnal variation on monocyte subsets and monocyte-platelet aggregates

Abstract

Background: Monocytes are important mediators in the pathophysiology of cardiovascular disease, but only scarce data are available on biological and methodological factors affecting their levels.

Design: Three monocyte subsets, CD14(++) CD16(-) CCR2+ (Mon1), CD14(++) CD16(+) CCR2(+) (Mon2), CD14(+) CD16(+) CCR2(-) (Mon3), and monocyte-platelet aggregates (MPAs) were analysed by flow cytometry. The effects of treadmill exercise were assessed on 12 healthy volunteers. Diurnal variation was evaluated in 16 healthy volunteers, and the effects of delayed blood processing were measured in 12 samples.

Results: Mon1 were increased when measured 15 min after exercise followed by a reduction at 1 h (P < 0·05 for both). MPAs were significantly reduced at 15 min and 1 h (P < 0·05 for both). There was significant diurnal variation in the numbers of Mon2, which were highest at 6 pm and lowest at 6 am. There were also significant diurnal variations in phagocytic activity of Mon1 and Mon2, which were highest at 12 pm and lowest at 12 am. Monocyte counts remained stable up to 2 h after venipuncture. MPAs were significantly increased at 2 h and increased further by 4 h after sampling.

Conclusions: Monocyte subset Mon2 and monocyte phagocytic activity undergo significant diurnal variation. A single bout of exercise causes a temporal increase in monocytes and a reduction in MPAs. Monocyte subset counts should be analysed within 2 h of blood sampling, whereas measurement of MPAs and monocyte CD14 and CD16 expression should be performed within 1 h.