Comparison of the Local and Systemic Immune Cell Alterations in Patients Undergoing Coronary Artery Bypass Graft Surgery

Background: The systemic inflammatory response after cardiac surgery is well studied. The important role of local intrapericardial immune cells in cardiac injury and cardiac remodeling has been suggested in previous studies. However, there is a paucity of data comparing the local and systemic inflammatory processes that happen before and after cardiac surgery.

Method: Twelve patients underwent on-pump coronary artery bypass graft (CABG) surgery, where native pericardial fluid (PF) and blood samples were collected immediately after pericardiotomy. A pericardial drain was placed in the pericardial space before closure. Post-operative PF and blood samples were collected 48 hours post-CPB. Flow cytometry was performed to determine levels and proportions of specific immune cells.

Results: In our patient population, we detected a variety of immune cells present in both PF and blood, which included neutrophils, two clusters of macrophages (CD163 high and CD163 low Mφ), dendritic cells, natural killer cells, T-cells, and B-cells. Native PF, seen as a plasma ultra-filtrate, shows major differences compared with blood considering the present immune cell proportions. CD163 high Mφ and T-cells predominantly occupy the native pericardial space, however, their systemic expression is significantly lower (CD163 high Mφ: p < 0.0001, T-cells: p = 0.0464). In contrast, neutrophils are the most abundant systemic immune cell type, yet only low levels were locally detectable (p < 0.0001). Postoperatively, the neutrophil population in the pericardial space increases drastically and equals the persistent high systemic expression. CD163 high Mφ (p = 0.0233) as well as T-cells (p = 0.0009) shift to higher systemic proportions after surgery and drop significantly in the postoperative PF. Interestingly, CD163 low Mφ are moderately expressed in both native PF and blood. However, we found an intrapericardial decrease of CD163 low Mφ and a systemic increase after surgery (p < 0.0001).

Conclusion: This study elucidates the differences in the local and systemic immune cell composition before cardiac surgery and their postoperative alterations. Our data helps better understand the intrapericardial immune cell re-population after on-pump cardiac surgery. It may also inform the connection to inflammatory driven postoperative complications, such as atrial fibrillation and pericardial adhesions.