In vitro phagocytosis competition: a turtle, a goose and a dog – who has the best score?

Phagocytosis is an effective innate immunity mechanism, that activates at the host’s initial contact with pathogen or foreign particle. In mammals’ blood, it is dominantly performed by neutrophils and monocytes. Avian and reptilian phagocytic potential is assisted by few other recognized phagocytes: heterophils equivalent to mammalian neutrophils, eosinophils, B lymphocytes, red blood cells and thrombocytes. The aim of this study was to compare in vitro phagocytosis by leukocytes, between three animal classes: reptiles, birds and mammals. Each group included six healthy animals of following species: turtle, goose and dog. Heparin blood samples (30 μL) were incubated with opsonized zymosan particles (6 μL, 1 mg/mL) for 15 minutes at 37°C and 15 minutes at room temperature, respectively. Differential leukocyte formula was assessed microscopically, using Romanowsky-stained blood smears. In vitro functional ability was compared based on the equivalent types of leukocytes that performed phagocytosis, as well as total phagocyte capacity (%) per 100 detected leukocytes on a blood film. The results presented neutrophils as the most active in canine blood (P=0.001), when compared with heterophils in turtles and geese. The turtles had both highest monocyte (P=0.002) and total phagocyte capacity (P=0.002), in comparison with the other two species. Total leukocytes were the highest in geese (P=0.003), but their active phagocytes had the least activity towards zymosan particles. Not only heterophils and monocytes, but also eosinophils, basophils and lymphocytes displayed phagocytic ability in turtles, indicating that reptile leukocytes have the most preserved phagocytosis potential across leukocyte types and among analyzed animal classes. ; Abstract Book