Neutrophilic Leukocytes and Neutrophil Extracellular Traps in Native Aortic Valve Endocarditis

Infective endocarditis is a disease that affects the endocardium and often alters heart valves, notably the aortic valve. Bacteraemia and valvular endothelial damage play an essential role in the pathogenesis of infective endocarditis. The pertinent literature suggests that neutrophil extracellular traps are important contributors to the development of the disease. However, features of the valvular damage and contribution of neutrophils to the alteration of cardiac tissue are not explored sufficiently. The purpose of this study was to investigate the occurrence and distribution of neutrophilic leukocytes and neutrophil extracellular traps in native aortic valves affected by infective endocarditis, using histopathology and immunohistochemistry assays. In addition, the presence of vegetations on the heart valve was determined. Infiltration of neutrophils into the valvular leaflet was significantly more severe at the free margin (mean 5.89 ± 3.00, p < 0.001) and the middle portion (mean 4.58 ± 3.64, p = 0.032) when compared to the base portion (2.05 ± 1.90). No significant differences in neutrophilic leukocyte infiltrating inflammatory lesions were found between cusp layers. The presence of myeloperoxidase and citrullinated histone expression characteristic of neutrophil extracellular traps was demonstrated by the use of immunohistochemistry in IE-affected valvular leaflets and vegetations. Collectively, the study results suggest that the free cusp margin and its middle portion of the aortic valve are exposed to enforced blood flow; endothelial damage and vegetation formation are likely to occur along with the presence of infective endocarditis-related bacteraemia.