Methods: We quantified the number of different maturating B cell subpopulations in arterial blood of 31 patients (23% women) with acute MI who were 66±15 years old. The study population included 14 patients with ST-segment elevation MI (STEMI) who were 64±14 years old and 17 patients with non-ST-segment elevation MI (NSTEMI) who were 68±15 years old. Myocardial ischemia was determined by coronary angiography. The left ventricular ejection fraction averaged 53% (range of 40-60%) in STEMI and 57% (range of 38-63%) in NSTEMI patients. Absolute cell counts were assessed in whole blood, drawn from the arterial port prior to coronary intervention, by multi-color FACS analysis. Mature CD19⁺ B cells were further subdivided in CD19⁺/IgD⁺/CD27^- naïve B cells, CD19⁺/IgD⁺/CD27^-/CD38⁺⁺/CD24⁺⁺ transitional B cells, CD19^+/IgD^-/CD27⁺⁺ plasma cells, and CD19⁺/IgD⁺/CD27⁺ memory B cells. Absolute quantification was achieved by means of blood analysis. Results were correlated with plasma markers of severity of myocardial damage. Additionally, 10 healthy individuals (30% women) were included who were 57±7 years old. The study was approved by the local institutional review board, and participants provided witnessed, written informed consent.

Results: Overall, the number of CD19⁺ B cells was significantly increased in STEMI patients compared to healthy controls (31.9±6.2 x10⁴ versus 13.6±3.3 x10⁴ cells/mL; p=0.026) and NSTEMI group (31.9±6.2 x10⁴ versus 15.9±2.1 cells/mL; p=0.016). Linear regression analysis was performed to correlate total B cell counts with troponin I and creatine kinase plasma levels in MI patients. The multivariate regression model comprised sex, age, current smoking, symptom duration, leukocyte count, and CRP-levels and revealed a strong correlation of the CD19⁺ B cell counts with the markers of the severity of infarction (ß-coefficients are given in table 1). Further investigation of B cell subpopulations revealed a continuously increased number of cells in STEMI patients compared to healthy individuals and to NSTEMI group (table 1). Noteworthy, only naïve B cells and memory cells show a correlation to troponin I (Pearson r=0.770; p=0.0005 and r=0.717; p=0.0058, respectively) and creatine kinase (Pearson r=0.827; p=0.0005 and r=0.717; p=0.0058, respectively), indicating a prevalent role for these subsets in myocardial damage after MI. Finally, the number of memory cells correlates to the 6 months probability of death from admission, which was calculated from the GRACE Score (Pearson r=0.609; p=0.0466).