Receptors to Interleukin-6 and Adhesion Molecules on Circulating Monocyte Subsets in Acute Myocardial Infarction

Purpose: Limited data are available on expression of receptors to adhesion molecules, a marker of endothelial cell activation, and cytokines by the three human monocyte subsets after MI. The interleukin-6 receptor (IL6r) has been implicated in the pathogenesis of atherosclerosis, a disease of inflammatory aetiology. We evaluated the dynamics of monocyte subset expression of receptors to vascular cell adhesion molecule (VCAM-1r), intercellular adhesion molecule (ICAM-1r), and IL6r after MI. Methods: Expression of VCAM-1r, ICAM-1r and IL6r was quantified by flow cytometry in patients with stable coronary artery disease (CAD,n=40) and on days 1, 3, 7 and 30 post ST-elevation MI (STEMI,n=50). Monocyte subsets were defined as CD14++CD16–(Mon1), CD14++CD16+(Mon2), CD14+CD16++(Mon3). Results: On day1 after STEMI, VCAM-1r expression was reduced on Mon1 (p=0.002), Mon2 (p=0.007), Mon3 (p=0.005). There was no change in monocyte ICAM-1r expression after MI, whilst its expression on Mon1 reduced by 30 days (p=0.001). IL6r expression was reduced on Mon2 after STEMI, with gradual upregulation on Mon1 and Mon2 during follow-up. Monocyte subset expression of receptors *p<0.05 vs day 3, †p,0.05 vs day 7, ‡p<0.05 vs day 30. Data presented as mean [standard deviation]. MFI, median fluourescent intensity. Conclusions: Circulating monocyte subsets involved in inflammatory responses appear to have reduced IL6r expression in the acute phase following STEMI. This may represent a regulatory feed-back mechanism aiming to re-balance the marked inflammation which is typically present after STEMI. There is also a decrease in VCAM-1r density on circulating monocytes after STEMI. This may reflect the selective homing of monocytes with high VCAM-1r expression to damaged myocardium.