Viability and cell death of synovial fluid neutrophils as diagnostic biomarkers in equine infectious joint disease: a pilot study

Synovial fluid samples from culture-confirmed infected joints (n=13), joints with pronounced non-infectious synovitis (n=11) and healthy joints (n=14) were collected from 24 equine patients and seven slaughterhouse horses. The samples from the joints with non-infectious synovitis and healthy joints served as negative controls. After isolation, counting and identification of neutrophils, the percentage viability, and the proportion apoptotic and necrotic neutrophils were determined by flow cytometry. Viability was significantly higher in infected samples compared to the controls. A significant difference in cell death type was observed, with apoptosis predominating in infected joints, and necrosis being more present in joints with pronounced non-infectious synovitis and healthy joints. The results of this pilot study suggest that flow cytometric analysis of neutrophil viability and cell death dynamics may assist the discrimination between infected and non-infected joints.