Detection of CD45+ cells in human atrial samples from patients with atrial fibrillation

Introduction: The processes underlying the initiation and development of atrial fibrillation (AF) are still not sufficiently explored. This most common arrhythmia is associated with an increase in mortality risk that is strongly related with old age. One of the generally recognized factors contributing to persistency of atrial fibrillation is structural remodelling of the myocardium. There is alteration in both cardiomyocyte morphology as well as changes affecting endomysium.

Aim: In this study we focused on morphological and functional changes in endomysium of atrial myocardium with special focus on immunohistochemical detection of CD45+- cells, representing the whole leukocyte population.

Methods: We analyzed atrial biopsies obtained from patients undergoing bypass or mitral valve surgery. The patients had a regular sinus rhythm or were suffering from atrial fibrillation. The atrial samples were fixed with 4% paraformaldehyde and embedded into paraffin. Sections from atrium were histologically examined using routine hematoxylin-eosin staining. CD45+ leukocytes were detected immunohistochemically. Threestep immunoperoxidase detection using mouse anti-CD45 monoclonal antibody (DAKO) was performed on paraffin sections after antigen retrieval.

Results: In all atrial samples from both groups examined in the pilot study we detected CD45+-cells in atrial myocardium as well as in endocardium and epicardium. The frequency of these cells was variable. Cells were either isolated or grouped in small clusters. Apparently, CD45+ cells formed a heterogeneous group of cells including those that can be clearly identified as lymphocytes and granulocytes. There were also large cells most likely represented macrophages and cells with elongated shape sending out long cellular processes, which may correspond to activated macrophages and/or dendritic cells. Some cells in the endocardium appeared to be crossing this layer on their way from the atrial cavity, while we observed only a small number of cells adhering to endocardial endothelium.

Conclusion: Our results document that CD45+ cells are a heterogeneous cell population in atrial myocardium from patients undergoing open heart surgery and these cells can be detected regardless of the heart rhythm. Additional markers will be employed to allow differentiation between various leukocyte subpopulations and their quantification.

This work was supported by the Research Program of Charles University.