Background: The plasma level of interleukin-6 (IL-6), a proinflammatory cytokine, has been reported to be elevated in patients with acute myocardial infarction (AMI). In addition to a specific cell-surface IL-6 receptor, a soluble IL-6 receptor (sIL-6R) exists in plasma as an extracellular domain of glycoprotein 80. The pathophysiologic roles of IL-6 and sIL-6R in AMI are still unknown.
Methods and results: We measured plasma levels of IL-6 and sIL-6R in 17 patients with AMI to evaluate changes over time at 11 points in the acute phase and compared them with parameters of inflammation, myocardial injury, and atherosclerosis. IL-6 showed a triphasic increase with peaks at 3 hours (276.2 +/- 50.0 pg/mL), 2 days (153.6 +/- 35.7 pg/mL), and 5 days (180.7 +/- 52.3 pg/mL) after the onset of AMI. sIL-6R had biphasic dips at 12 hours (31.1 +/- 4.1 ng/mL) and 3 days (29.9 +/- 1.5 ng/mL) after the onset on AMI. The time-dependent changes in IL-6 paralleled those in sIL-6R from onset to 5 days. Thereafter, the changes in IL-6 and sIL-6R varied; that is, IL-6 gradually decreased from 5 days to 4 weeks, whereas sIL-6R gradually increased from 5 days to 4 weeks. Significant positive correlations were observed between the absolute increase in IL-6 and the decrease in sIL-6R and the changes in white blood cell count, erythrocyte sedimentation rate, C-reactive protein, creatine kinase, and lactic dehydrogenase. Neither IL-6 nor sIL-6R strongly correlated with parameters of coronary atherosclerosis.
Conclusions: These results demonstrate that IL-6 and sIL-6R are associated with the processes of inflammation and myocardial injury during the acute phase of AMI.