Flow cytometric analysis of the neutrophil respiratory burst of ayu, Plecoglossus altivelis: comparison with other fresh water fish

Neutrophils of vertebrates undergo respiratory burst activity (RBA) as a defense mechanism against bacterial infections. We report here that ayu (Plecoglossus altivelis) have unusually high RBAs even when they are in a healthy condition. Kidney and blood leukocytes were obtained from ayu, rainbow trout (Oncorhynchus mykiss), carp (Cyprinus carpio), eel (Anguilla japonica), and pond smelt (Hypomesus nipponensis). Neutrophil RBA was measured by flow cytometry using dihydrorhodamine after stimulation with phorbol myristate acetate. The amount of RBA of neutrophils from both blood and kidney was significantly higher in ayu than in the other species (e.g. the fluorescence intensity of ayu blood neutrophils was about 3–7 times higher than that from trout and carp, and that of ayu kidney neutrophils was 2–19 times higher than that of rainbow trout, carp, eel, and pond smelt). This unique character of ayu neutrophils was invariable even at different ages, locations, and sex-maturation stages.